Appended below are the 6 BBS referee reports on the second revision of your manuscript: "Gestalt Isomorphism and the Primacy of the Subjective Conscious Experience."

The reports indicate that your manuscript is improved, but it is still requires some work if it is to be suitable for BBS Commentary. The remaining revisions will not be re-refereed: I myself will review the final draft to see whether these problems have been remedied:

(1) The present revision clearly was not responsive to a number of substantive referees' points (mainly philosophical and conceptual ones, but also calls for more concreteness and more explicit comparison with rivals) that I had singled out among the first round of refereed reports. This is a little worrisome for a BBS target article, as BBS target articles, unlike conventional journal articles, are meant to be written specifically to elicit and respond to peer commentary. The assumption is that the author seeks and will be responsive to the commentary (whether to accept it or to rebut it) and that the exchange will be useful to the field. In your revised draft you chose to ignore certain substantive criticisms on grounds of "paradigm shift". In your final draft I will be looking to see whether this is still the case, as if so, then it suggests that this work is unlikely to elicit a substantive interaction with commentators that will be useful to the field and hence should appear in a conventional journal rather than a peer-commentary journal.

(2) A central example of the sort of philosophical/conceptual point on which the present draft appears to be far too hasty is what several referees mention as the content/vehicle distinction: In talking about isomorphism you sometimes seem to be conflating the properties of the representing object (e.g., a picture) with those of the represented object (e.g. what the picture is a picture of). This must be disambiguated and clarified very explicitly in the revised draft, otherwise all further discussion of "isomorphism" becomes moot. You are also asked to address the question of Shepard's "2nd-order" isomorphism, which has been much discussed in the pages of past issues of BBS (e.g., Shepard, Edelman). I also suggest you give some explicit consideration to the problem of the commensurability of physical and felt properties which lies at the heart of any isomorphism proposal like yours (Palmer, Pylyshyn).

(3) Although sometimes simply inserting a reference is sufficient, when it comes to substantive points, it is better to discuss them substantively. In particular, criticisms and rival views should be addressed explicitly and substantively. You need to show commentators how your view gets around standard objections, and how it does so better than its relevant rivals. And on the question of predicitiveness, you must be explicit as to whether this is one of your view's virtues, or whether it is merely consistent with what we already know, rather than actually generating any new predictions. It is not sufficient to keep saying it's a new paradigm and will be appreciated in its time. The time for commentators is now.

Let me stress, you need not persuade me or the referees that you are right in every instance, only that you have understood and taken seriously and self-critically the substantive problems that have been raised for your view.

For the details, please see the 6 thoughtful referee reports. [Please make sure you read these reports in an HTML reader, otherwise the boldface will not be visible. If the word "boldface" does not appear in boldface in this sentence, please contact BBS.] I have also annotated your response to the prior referees, after the present round of reports,

Please let us know how you propose to proceed, and according to what timetable. The editorial review of your final draft will be prompt, but it will also be final (no further rounds of revision will be possible), so I urge you to be responsive to the bodlfaced points (including those in my annotations on your response to the prior round of referee reports).

Sincerely,

Stevan Harnad Editor, BBS

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Author : Steven Lehar Title : Gestalt Isomorphism and the Primacy of the Subjective Conscious Experience: A Gestalt Bubble Model
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Referee #1 Anonymous

The basic idea of this paper certainly is an excellent one: to directly introduce phenomenological constraints into theoretical models of neurophysiological mechanisms. Directly modeling perceptual structures within neurocomputational models of brain function certainly is necessary, but it also limits the explanatory domain to consciousness only and to those mechanisms, which essentially need conscious experience to fulfil their function. Being a philosopher, I will not comment on the question of how sound Lehar's proposal is from a strictly computational perspective. I will confine myself to some general remarks about how the paper might be improved.

The introduction is a bit too long, and should be compressed, in particular the philosophical name-dropping. In sections 3 and 4 a special problem of this paper becomes more and more obvious: It just mentions many different authors, but never proceed to tackle one problem in depth. It is not obvious what all the citations contribute to the author's own point (which is interesting). In section 5 more attention should given to the idea of modeling conscious experience "directly" (introspection is conscious experience itself, and a highly mediated process--what precisely is "direct" here?). Second, it would be interesting to hear more about the notion of an isomorphism in this section.

For instance, there are not only structural and functional ismorphisms, but higher-order ones as well [Shepard, Edelman]. Just the fact that Wolfgang Kohler argued for a certain type, is not a good argument for the author to simply accept this notion. This is decisive for his project: Why this mapping? Sections 6 and 7 offer interesting, but cursory remarks on many different issue, and for the reader it is possible to lose sight of what Lehar actually wants to say--I propose to put his thesis in focus, more crisply, and then directly relate all these remarks to this thesis: Why are they relevant?

In section 8 we find the author's own "Gestalt bubble model". At this point I have to excplicitly recommend a second reviewer, who can assess if this model is sound and/or promising from purely mathematical and computational perspective. It looks highly interesting to this reviewer, but it may not be explicit enough or trivial from a state-of-the-art mathematical perspective.

The discussion section suffers from a defect found earlier on, namely that many different findings and authors are touched upon briefly, but unfortunately not directly related to the author's thesis. For all of these examples it should be made very clear what the Gestalt bubble model here proposed actually offers in terms of an explanatory advantage over other, already existing theories. The conclusion is convincing to the present reviewer, but it might be better to explicitly show how other theories can not satisfy the phenomenological constraints mentioned at the beginning of the last paragraph, and how therefore the proposed model has the advantage of a higher degree of constraint satisfaction.

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Referee #2 Opie, Jon <jon.opie@adelaide.edu.au>

In my original report (co-written with Gerard O'Brien) I indicated that in my view Lehar's manuscript is worthy of BBS treatment; that it is in some respects quite novel, and likely to generate a significant amount of critical reaction and commentary across a broad range of disciplines. My view has not changed, but then neither has the manuscript, to any significant degree.

My original response contained a number of criticisms and suggestions, divided into two categories: Minor and Major. In his rewrite Lehar has addressed many of the Minor issues, and NONE of the Major ones. This is, to say the least, a little disappointing. The BBS refereeing process normally gives an author a taste of what they might expect to meet in open commentary. Referees can be regarded, in part, as trial commentators. Like commentators, they may differ with the author on some issues, they may have some quite legitimate concerns and criticisms of the author's approach, and they will presumably not fully appreciate or understand everything the author is trying to do. For this reason, it is to the author's advantage to fully engage with his referees. This means RESPONDING to their suggestions and concerns. An appropriate response can take two forms: it can involve modifying the ms in some way, or EXPLAINING (in a covering letter) why it has not been possible to accommodate a particular concern/criticism in the text. Normally, even where the author feels that a referee has misunderstood his position, SOME modification of the text is called for (e.g., a footnote or parenthetic remark) so as to avoid similar misunderstanding in other readers.

Lehar's response is, therefore, not really adequate. He has missed a useful opportunity for communication and clarification. Having been through the BBS refereeing process myself, I can sympathise with Lehar's frustration at its length and complexity. Even so, I found his covering letter to be unsatisfactory. I am not an "anonymous judge", nor did I ask Lehar to address the "full implications of his proposed model to [any] specialty domain". Moreover, I take myself to be an ally, in that I regard myself as, broadly speaking, a proponent of the paradigm he defends. My response was offered in a constructive spirit, and designed to minimise misunderstanding among commentators (especially those, like myself, who are philosophers), and to increase the overall coherence of the position.

My remaining concerns fall under two heads:

SCHOLARSHIP/ORIGINALITY

At the beginning of section 9 Lehar remarks that:

"the computational transformations observed phenomenologically are implausible in terms of contemporary concepts of neurocomputation and even in terms of computer algorithms"

In my original report I mentioned that work in connectionism, a neurally inspired computational framework, holds out the promise of implementing a gestalt bubble model of subjective experience because it trades in constraint- satisfaction style processing. Connectionism has been around since at least the early eighties, so it might bear mentioning. The references I gave in my original report suggest that at least a few people are interested in applying connectionism to gestalt phenomena in perception. The work of Wolf Singer is also explicitly targeted at finding a neural basis for gestalt phenomena. I think Lehar should at least mention some of this work, even if only by way of a footnote.

REASONING

Lehar says:

Sect.8.8 the Gestalt Bubble model "is more a quantitative description of the phenomenon rather than a theory of neurocomputation"
Sect.9 "the Gestalt Bubble model offers a mathematical framework for a precise description of the information encoded in these elaborate spatial percepts, independent of the confounding factor of neurophysiological considerations"
Sect.5 "The isomorphism required by Gestalt theory is not a strict structural isomorphism, i.e. a LITERAL isomorphism in the physical structure of the representation, but merely a functional isomorphism"

On the other hand, Lehar also speaks of:

Sect.5 "spatial representation"
Sect.6.1 "data expressed in spatial form", "the spatial nature of the perceptual representation"
Sect.6.2 "perception as a LITERAL volumetric replica of the world inside your head"
Sect.8.1 "a three-dimensional pattern of opaque state units"
Sect.8.6 "an explicit three-dimensional REPLICA of the surface"
Sect.9 "the three-dimensional nature of the encoding and processing of mental imagery" and "a volumetric spatial medium"

There is an apparent inconsistency between the first set of quotations and the second. If the Gestalt Bubble model is a "quantitative description", "a mathematical framework" that does NOT require a "literal isomorphism in the physical structure of the representation", then it is hard to see why Lehar talks of "literal volumetric replicas", "three-dimensional replicas", "a...spatial medium" and so on.

One possibility is that Lehar is just being careless about what philosophers know as the vehicle/content distinction. The content of a representation is its meaning or the information it carries (what it is about). A representational vehicle is some physical thing that functions as a representation. One normally wants to avoid confusing the properties of a representation qua vehicle with the content it carries. A photograph, for example, has properties (e.g., being flat, being made of paper, etc.) not necessarily shared with the thing it represents. A representation that is merely functionally isomorphic to the thing it represents need not have any significant properties in common with that thing. Talk of "three-dimensional replicas" and "spatial media" sounds like a reference to properties of the representational vehicles, rather than their contents, which seems inconsistent with the claim that a Gestalt Bubble model only seeks to mathematically formalise the information content of perception. "Spatial representation", on the other hand, is ambiguous between a representation OF space (the content), and a representation that employs spatial properties of the vehicle to represent something (e.g., spatial features of perception).

If this suggestion is right then Lehar needs to remove or comment on vehicle/content ambiguities where they occur, and recast what sounds like discussion of vehicle properties in terms of contents or information. On the other hand, if Lehar is committed to some claim to the effect that spatial relations in the brain are used to represent spatial relations in perception, then he needs to square that in some way with the first set of quotations above (remembering that spatial properties of neurons and neural networks are "neurophysiological considerations").

On a related point, in Section 6.1 the author says that "to deny the spatial nature of the perceptual representation in the brain is to deny the spatial nature so clearly evident in the world we perceive around us". There is a vehicle/content ambiguity here concerning the expression "spatial nature". The material that immediately follows suggests that Lehar has in mind the spatial nature of the CONTENTS of perception, rather than the vehicles of perception (whatever they might be). However, if it is the spatial nature of the contents of perception Lehar has in mind, it is hard to see why anyone would deny that. Controversy has tended to arise over much stronger claims, such as that space is represented via structural,topographical or topological isomorphism.

The author will have to decide how to address these issues. If he believes I have misunderstood him then, at the very least, a few clarificatory footnotes would be in order, although I suspect that something more substantial may be inorder.

To conclude, this is a fascinating ms, which contains some novel suggestions about the structure of perceptual experience, and about the means by which we might formalise that structure. I certainly would not want the concerns I've raised to stand in the way of publication, although I think that the author will avoid some unnecessary discussion in open commentary if he is able to accommodate them in some way.

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Referee #3 Anonymous

I have been asked to re-review Steven Lehar's BBS paper. Unfortunately, as far as I can tell, the author is unwilling to meet the challenge to improve his manuscript and address the reviewer's points. We all know of the problems of the peer review process, but simply refusing to address *constructive* criticism is unacceptable. If the author is asking for the paper to be accepted as is, my position is unchanged and I cannot recommend it for publication.

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Referee #4 Anonymous

The paper is somewhat improved from the previous version (which was not bad in itself). Although the author has not elaborated every point mentioned by the referees, he may be right in pointing out (in his letter) that it is simply impossible to examine in extensive detail all of the myriad implications of his approach and incorporate them into the scope of the present manuscript.

Therefore, I would be inclined to recommend that the paper is accepted in its present form and that the rest of the open issues are left for the commentary round. The paper seems to me sufficiently strong and clearly argued to deserve open peer commentary at this stage. Although the topic is certainly extremely controversial, I am sure it will stimulate fruitful discussion across several different disciplines. Compared with some of the recent alternative views on visual perception and consciousness (e.g. Pessoa et al., O'Regan & Noe), Lehar's approach is, although entirely different, at least equally plausible. Furthermore, it represents an important revival of the philosophy of perception that the great Gestalt psychologists originated, but which has been largely ignored in modern cognitive neuroscience.

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Referee #5 Anonymous

Lehar's perceptual modelling approach provides a useful intermediary between phenomenal experience of a spatially extended 3D world and neuronal activity. There must be a higher order emergent level of brain activity that proximally supports our normal integrated experience, and a spatial virtual-reality replica of the external world is one plausible candidate. Lehar is also right to argue that the first step in finding broad neural state-phenomenal state correspondences must be to systematise the phenomenology. His gestalt bubble model forms an interesting attempt at modelling the properties of phenomenal space - and, in my view, an amended version of this paper merits publication in BBS.

However, in its present form, the paper presents a rather disturbing mix of insightful writing and careful scholarship on some issues, with dubious scholarship and a series of non-sequiturs on other issues (particularly the broader philosophical issues developed in Sections 1 to 7). The latter really need detailed attention before the paper is suitable for publication. As I believe the paper to be worth the effort I have listed what seem to me to be the obvious problems below. I hope that the author won't be discouraged by my detailed critique, and either clarifies or modifies his argument or pre- emptively answers the detailed points below.

Specific points that the author needs to address

Section 1, para 4: Lehar writes "The modern view is that mind and brain are different aspects of the same physical mechanism. In other words, every perceptual experience, whether a simple percept such as a filled-in surface, or a complex percept of a whole scene, has two essential aspects; the subjective experience of the percept, and the objective neurophysiological state of the brain that is responsible for that subjective experience. Like the two faces of a coin, these very different entities can be identified as merely different manifestations of the same underlying structure, viewed from the internal first- person, v.s. the external third-person perspectives."

Problems: A problem of scholarship - This is ONE modern view, not THE modern view - the main current alternatives being the many reductionist forms of physicalism and functionalism. Lehar should reference prior work that his own writing extends. His complementary first- versus third-person dual-aspect theory of information closely resembles that introduced in BBS by Velmans, 1991 (although Velmans would not describe his position as physicalism); it also resembles Searle, 1997 (although the latter rejects the notion that his view is dual-aspect); it also resembles Chalmers, 1996 (although the latter describes himself as a naturalistic dualist).

Lehar then writes "The dual nature of a percept is analogous to the representation of data in a digital computer, where a pattern of voltages present in a particular memory register can represent some meaningful information, either a numerical value, or a brightness value in an image, or a character of text, etc. when viewed from inside the appropriate software environment, while when viewed in external physical terms that same data takes the form of voltages or currents in particular parts of the machine.

Problem: A false analogy? Lehar should at least acknowledge or counter Searle's argument that computer symbols are not in fact meaningful to the computer - indeed as Searle, 1997 notes "a computer isn't even a computer to a computer."

Section 2: Lehar writes "To take a concrete example, consider the vivid spatial experience of this paper that you hold in your hands. The question is whether the rich spatial structure of this experience before you is the physical paper itself, or whether it is an internal data structure or pattern of activation within your physical brain."

Problem: There is a non sequitur here. Many representationalists would accept that "the vivid spatial experience of this paper that you hold in your hands" is not the "physical paper itself", for the reason that modern physics gives a representation of the entity itself that is very different to how it is perceived. However, accepting this does not require one to accept that the rich spatial structure of the experienced paper is reducible to "an internal data structure or pattern of activation within your physical brain." The internalist vs externalist vs projectionist debate hinges on different issues (see below).

Section 2.1 para 2: Lehar writes "In exactly analogous manner the pattern of electrochemical activity that corresponds to our conscious experience can take a form that reflects the properties of external objects, but our consciousness is necessarily confined to the experience of those internal effigies of external objects, rather than of external objects themselves."

Problems: There are two more non-sequiturs here: Strictly speaking, internal electrochemical activity correlates with conscious experience rather than corresponds to our conscious experience. The latter term begs the question regarding the correctness/incorrectness of physicalist reductionism. Whether or not physical reductionism is true, such representations "can take a form that reflects the properties of external objects". However it does not follow from this that "our consciousness is necessarily confined to the experience of those internal effigies of external objects, rather than of external objects themselves." Rather, it makes more sense (within representationalism) to suggest that our conscious experiences of external objects are indeed experiences of those objects. These experiences might correlate with or might the first-person aspect of internal effigies of external objects, but the experiences are not of those internal effigies (this confuses the nature of internal representations with what these are representations of).

Lehar appears to make the same error in Section 2.4, where he seems to misunderstand Searle: He writes "It is the implicit or explicit acceptance of this naive concept of perception that has led many to conclude that consciousness is deeply mysterious and forever beyond human comprehension. For example Searle (1992 p. 96) contends that consciousness is impossible to observe, for when we attempt to observe consciousness we see nothing but whatever it is that we are conscious of; that there is no distinction between the observation and the thing observed." In fact Searle is not being naive but merely pointing out the obvious - that experiences are in a sense "transparent" - that when we look at this paper we observe this paper not our experience of this paper. Or to put it more accurately, the paper that we see is what we experience. From a third- person perspective we can observe representations of things in the world in the brains of others, but from a first-person perspective we can only observe the things in the world (what the representations are of).

Section 2.2, para 1: "The indirect realist view is also incredible, for it suggests that the solid stable structure of the world that we perceive to surround us is merely a pattern of energy in the physical brain, i.e. that the world that appears to be external to our head is actually inside our head."

Problem: This is another non sequitur: it does not follow from the fact that a pattern of energy in the physical brain causes or correlates with the solid stable structure of the world that we perceive to surround us, that "the world that appears to be external to our head is actually inside our head." This confuses causation, correlation and ontological identity (Velmans makes this point in his 2000 book). It also takes for granted an outmoded push-pull notion of causality (in which effects have to be spatially located where the causes are), i.e. it assumes that if the causes of experience are in the brain the experiences must also be there. This works for billiard balls that cause each other to move by mechanical impact, but not for gravity (action at a distance), the relation between electrons moving inside a wire and the magnetic field outside the wire, non-local effects in quantum mechanics etc.

Lehar is right to note that if we accept that what we perceive is inside our heads, then the boundaries of our real head must be beyond what we perceive. But he is wrong to suggest that these are the necessary consequences of indirect realism. One can be an indirect realist or a critical realist without accepting that the phenomenal world is really inside our head. Lehar simply asserts that the latter follows from indirect realism without giving any justification. Given that, phenomenologically, the reverse is true (our heads appear to be inside a surrounding phenomenal world), and given that causes and correlates need to be distinguished from identities, he needs to do some work in this department. Section 2.3.

In discussing Velmans' projection theory (an alternative to Lehar's proposal) Lehar writes "Velmans insists that perceptual projection is a subjective psychological effect produced by unconscious cognitive processing, and that nothing physical is actually projected from the brain. This really confounds the question of whether anything is projected at all."

Problem: Lehar does not make what is confounded clear. Velmans separates third-person physical causes from first-person psychological effects, and states that perceptual projection is a first-person psychological effect. That is, from a given observer's perspective, the physical world looks like it is outside the head (not inside it). However, viewed from a third-person perspective, nothing physical is projected from the brain.

Lehar goes on to write "Smythies (1954) points out the fallacy of this theory, for if by 'projection' we mean that the brain `knows' that physical objects are external to the organism, this would not explain the basic fact that the end results of the physiological processes of perception are spatially outside the physical organism."

Problem: Poor scholarship here. As far as I know, Velmans never claims that the brain 'knowing that physical objects are external' somehow 'explains' perceptual projection. Rather, he suggests that mental modelling is responsible for projection and has suggested virtual reality systems as useful analogies (e.g. in his 2000 book). In terms of an explanatory mechanism this is exactly the same proposal that Lehar himself favours. So this presents a distorted view of the literature. As far as I can judge, the real difference between Lehar and Velmans is not about what might be a plausible explanatory mechanism for projection. Rather it is about the nature and location of the experienced effects.

Lehar goes on to write "Unless the principle of external projection can be demonstrated in a simple artificial sensory system, this explanation too remains as mysterious as the property of consciousness it is supposed to explain."

Problem: This test begs the question - unless one is a reductive functionalist. No first-person qualia can be demonstrated to exist in a simple artificial system by an exclusively third-person test. Artificial systems might have qualia, including a 3D phenomenal world, provided that their representational structures are appropriate - but to know whether they have such qualia we would have to be those systems (the problem of other minds).

Section 2.4 Lehar puts the importance of the issues well in this section. It is indeed "of vital importance to reach a consensus on the nature of the explanandum of psychology before we can attempt an explanans. In particular, we must decide whether the vivid spatial structure of the surrounding world of visual experience is an integral part of the psyche and thus within the explanandum of psychology, or whether it is the external world itself, as it appears to be naively, and thus in the province of physics rather than of psychology."

Problem: However, Lehar again goes on to suggest a false distinction between the projectivist position and his own in implying that only his position takes the 3D perceived world to be part of the explanandum of psychology. The actual difference between these positions is that Lehar goes on to claim that such experience must be in the head in spite of how they seem, while the projectivists claim that experiences are really how they seem.

In the next section, Lehar again misrepresents the projectivist position. He writes, "The problem with the direct realist view is of an epistemological nature, and is therefore a more fundamental objection, for direct realism as defended by Gibson is nothing short of magical, that we can see the world out beyond the sensory surface. The projection theory has a similar epistemological problem, and is equally magical and mysterious, suggesting that neural processes in our brain are somehow also out in the world." To my knowledge, neither the projectivists nor anyone else make such an absurd claim (projectivists claim phenomenal effects to be out in the world, not neural processes).

Lehar goes on to write "Both of these paradigms have difficulty with phenomena of dreams and hallucinations (Revonsuo 1995), which present the same kind of phenomenal experience as spatial vision, except independently of the external world in which that perception is supposed to occur in normal vision." In fact, Velmans would agree with Lehar about likely projective mechanisms (see above) and actually cites dreams, hallucination and VR systems as exemplars of perceptual projection. [See also BBS's recent sleep/dreaming issue, including Revonsuo's target article therein.]

Lehar goes on to write "If we accept the truth of indirect realism, this immediately disposes of at least one mysterious or miraculous component of consciousness, which is its unobservability. For in that case consciousness is indeed observable, contrary to Searle's contention, because the objects of experience are first and foremost the product or "output" of consciousness, and only in secondary fashion are they also representative of objects in the external world."

Problem: This is a non-sequitur. Indirect realism is an epistemology (a theory about the mediated nature of perception and cognition). Adopting it (or not) is tangential to the issue of whether consciousness is observable. In any case Lehar does not make it clear whether he means observable to an external observer (in the manner of brain states) or whether he means observable to the subject who has those conscious experiences. The latter are in any case observable in the sense that a subject can report on what he experiences - Searle's point is simply that there is nothing over and above that to report.

What Lehar means by "the objects of experience are first and foremost the product or "output" of consciousness" also needs clarification (how can the objects of consciousness also be the product of consciousness?).

Lehar goes on to write, "Searle's difficulty in observing consciousness is analogous to saying that you cannot see the moving patterns of glowing phosphor on your television screen, all you see is the ball game that is showing on that screen. The indirect realist view of television is that what you are seeing is first and foremost glowing phosphor patterns on a glass screen, and only in secondary fashion are those moving images also representative of the remote ball game."

Problem: A misrepresentation of Searle. Searle would not deny that conscious experiences can be observed (as conscious experiences) in the sense that they can be reported on. At the same time he would accept that many experiences also represent objects and events in the world (they are intentional).

[In any case, in Section 4 Lehar goes on to accept that one cannot observe phenomenal states directly even in the modelling approach that he proposes when he writes "The isomorphism required by Gestalt theory is not a strict structural isomorphism, i.e. a literal isomorphism in the physical structure of the representation, but merely a functional isomorphism, i.e. a behavior of the system as if it were physically isomorphic (Kohler 1969, p 92). For the exact geometrical configuration of perceptual storage in the brain cannot be observed phenomenologically any more than the configuration of silicon chips on a memory card can be determined by software examination of the data stored within those chips."]

Lehar goes on to write, "The choice therefore is that either we accept a magical mysterious account of perception and consciousness that seems impossible in principle to implement in any artificial vision system, or we have to face the seemingly incredible truth that the world we perceive around us is indeed an internal data structure within our physical brain."

Problem: A poor account of the choices - which is a serious weakness for a potential BBS target article. As noted above, Lehar creates a misleading account of alternative positions in order to bolster his contention that his own position is the only tenable one. Section 6.2. Lehar writes "The dome of the sky above, and the bowl of the earth below therefore define a finite approximately spherical space (Heelan 1983) that encodes distances out to infinity within a representational structure that is both finite and bounded. While the properties of perceived space are approximately Euclidean near the body, there are peculiar global distortions evident in perceived space that provide clear evidence of the phenomenal world being an internal rather than external entity." In 6.3 he also writes "The appearence of perspective in the three-dimensional world we perceive around us is perhaps the strongest evidence for the internal nature of the world of experience, for it shows that the world that appears to be the source of the light that enters our eye, must actually be downstream of the retina, for it exhibits the traces of perspective distortion imposed by the lens of the eye, although in a completely different form."

Problem: Lehar again confounds the issue of how well the phenomenal world constructed by the brain models the world described by physics, with the issue of whether the phenomenal world is itself in the brain (projectivism takes the same view that he does about the former without requiring the latter).

The Conclusion: Lehar claims that "this is not a model that makes no predictions. Indeed this model, even in its present general form makes the following very specific predictions" - but then goes on to list a range of phenomena that are not predictions at all, as they have already occurred and are readily observable. In short, he should claim that his model is consistent with the existing phenomenal evidence (rather than it making "predictions" about as yet unobserved events). Indeed he admits as much by going on to write "These "predictions" are so immediately manifest in the subjective experience of perception that they need hardly be tested psychophysically."

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Referee #6 Held, Dick <HeldD@ncopost.ne-optometry.edu>

By now I have read Lehar's latest revision several times and have similarly gone over the reviews of the referees and replies of the author thereto.

The revision is extensive and I believe on the whole does justice to the reviewers comments. In more detail:

Referee #1 Lehar's response to this critique is that while several of the requested additions might deal with interesting material, they are not essential to his paradigmatic stance and, in fact, would make the article inordinately long. Others are debatable and simply confirm that this manuscript is provocative and will elicit interested responses.

Referee #2 Lehar has answered these referees quite extensively. In many cases he accepts the criticism and has revised accordingly. In other cases he continues to debate the issues.

Referee #3 Lehar has responded to this reviewer by removing some philosophical material and as in response to #1 arguing that the requests are either too vague or go beyond the demands of the intent of his subject matter.

Referee #4 Lehar applauds. This referee has not changed his favorable opinion since his original reading of the manuscript.

Overall I believe that Lehar has done justice to the comments of his referees. He is somewhat prickly in his responses but that is a stylistic factor and I don't think bears on the substance of the issues. Many of the referees responses could already be used as rejoinders in the style of the Journal as can the authors responses as well. As he says many of the referees responses confirm the interest the manuscript will generate.

Since all of the reviewers feel that the manuscript is publishable in some form, it seems to me that it is now ready for publication.

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[1] SUITABILITY : ACC 2 4 5 6 MIN 1 MAJ NOT N/A 3

[2] PRESENTATION : ACC 1 2 4 5 6 MIN MAJ NOT N/A 3

[3] SCHOLARSHIP : ACC 4 6 MIN 1 2 MAJ 5 NOT N/A 3

[4] DATA/METHOD : ACC 2 4 5 MIN MAJ NOT N/A 1 3 6

[5] REASONING : ACC 1 4 6 MIN 2 MAJ 5 NOT N/A 3

[6] THEORY : ACC 1 2 4 6 MIN 5 MAJ NOT N/A 3

[7] LENGTH : ACC 1 2 4 5 6 MIN MAJ NOT N/A 3

DISPOSITION : ACC 4 6 MIN 1 2 MAJ 5 NOT 3 ELS

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Here are a few editorial comments on the author's cover letter in response to the prior round of referee reports. These comments are intended to help in the final revision:

I am encouraged that most of the reviewers seem to recognize the potential significance of my paper to the larger issues of perception and consciousness. One reviewer endorses the paper outright. The remaining reviewers offer conditional endorsements, contingent on the addition of an extraordinary quantity of additional explanation on a variety of diverse subject areas, the general complaint being that I have not addressed the full implications of the proposed model to various specialty subject domains. But the real problem here is that what is being proposed is not so much a theory, as it is a paradigm, i.e. I propose to challenge some of the foundational assumptions of contemporary psychology and neuroscience, and thereby to establish a whole new direction for the investigation in those sciences. Consequently this proposal necessarily has implications across a wide range of disciplines, including psychology, neuroscience, and the philosophy of consciousness, many of which will probably take decades to fully come to light. But there is simply no space to address all of those implications exhaustively in a single paper.

Reviewers comments unindented roman; author's comment indented italics, editor's comment unindented boldface.

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Referee #1 anon
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[ED: As Referee #1, who is referee #4 in the latest referee reports, now says he requires no more revision, I will make no comments on this exchange. Please go on to Referee #2. Ed.]

Note: This document is also avaliable on-line at http://cns-alumni.bu.edu/pub/slehar/webstuff/bubw/rebut2-0.html where hyper-links to additional source material are provided.

in the introduction, the author claims that theories of synchronous oscillations are not yet specified sufficiently to know exactly how they address the issue of perceptual representation. i think this ignores recent advances in the field that should be discussed. for example, roelfsema & singer (1998, cerebral cortex 8: 385-396) present a detailed model of the gestalt phenomenon of connectedness in defining coherent objects, and propose neural synchronization as the mechanism behind this phenomenon. it seems that the mechanism they propose produces neural representations isomorphic with the objects subjectively perceived. furthermore, singer's group (e.g. engel et al 1999; consciousness and cognition 8: 128-151) hypothesize that coherency of neural activity may be the gateway to consciousness. how do these models and ideas relate to the gestalt bubble model?
 

Although the phenomenon of synchronous oscillations between cortical neurons is indeed suggestive of some Gestalt process (Lehar 2001) the only computational function performed by neural synchrony, as proposed by Roelfsema & Singer, is to label regions in a two-dimensional image which are explicitly connected. The computational functionality of this process is very simple, nothing more than a diffusion of information throughout the connected region. Now the synchrony theory is interesting for a number of reasons (Lehar 2001). However that theory says nothing about the kind of connectivity observed in Gestalt illusions such as the Kanizsa figure, where the illusory percept emerges between visual elements which are *not* explicitly connected. The volumetric spatial reification function of the Gestalt Bubble model, which is based on global configural factors not involving explicit connectivity, is so far removed from the simple labeling of connected regions in two dimensions that I stand by my statement that "it is hard to see how this paradigm, at least as currently conceived, can account for the solid three-dimensional nature of subjective experience".

the author's treatment of spatial hemineglect remains too superficial and includes no references to the most recent original literature on this matter. he does not mention, although he should, that one of the traditional explanations of neglect in the literature is that "conscious representations of contralesional space may be more or less completely lost" (vallar 1998, trends in cognitive sciences 3, p. 87).

that idea would seem to be identical to the one offered by the author. however, in recent years it has been noted that the disorder's manifestations are very complex and that "it fractionates to a number of discrete patterns of impairment" (vallar p. 88).

in fact, lehar's suggestion that hemineglect could be explained by "damage to a left half of a three-dimensional imaging system *used both for perception and the generation of mental imagery* has already been contradicted by the evidence. there are cases of *dissociation* between hemineglect in mental imagery and visual perception (e.g. coslett 1997, brain 120: 1163- 1171; beschin et al. 1997, cortex 33: 3-26). therefore, it would seem that perception and imagery do not depend on one single spatial representation. how can the bubble model handle this complication?

furthermore, there are peculiar dissociations as to what the neglect patient can and what he cannot perceive; for example many patients can describe the global gestalt of a figure, but when copying its local features, leave those on the left side out (marshall & halligan 1995, nature 373: 521-523). present accounts of the multiple forms of neglect refer to several spatial maps and their interaction (e.g. ladavas et al. 1997, experimental brain research 116: 493-500). to make the bubble model truly relevant for the description and interpretation of hemineglect, it should be explicitly connected with these latest findings and models of the phenomenon, rather than a textbook-level general description. otherwise it remains unclear whether the bubble model adds anything to traditional descriptions and explanations of neglect.
 

This is exactly the same criticism that this same reviewer raised in the first round of review. I gave a complete answer to this objection in the last response. **HELLO? IS ANYBODY READING THIS?** (Or am I just talking to myself?) For the reviewer's benefit I will copy my response to this same issue from my last response to him, I hope this time he will find an opportunity to read it, and address his response to my answer, instead of just restating his original complaint.

Section quoted from last response begins here:
 

The phenomenon of neglect was introduced at the very end of the paper in the discussion section, i.e. this is not the central focus of the paper. I do not propose to account for all of the subtleties of the neglect syndrome with a single simple explanation. However there is an undercurrent in the debate on neglect as to whether the phenomenon is spatial at all, or merely "attentional", and the basis for this debate is ultimately neurophysiologically motivated, i.e. it is difficult to imagine how explicit volumetric images could possibly be encoded in the brain, especially images that can rotate and translate with respect to each other in a non- anchored manner. It would be very convenient for neural network theorists if the neglect syndrome could be wished away, which would conveniently dispose of its troublesome implications. Similar objections are often raised with regard to mental imagery.

But the troublesome issue of neglect is not that half of space is missing, but that it highlights the fact that there is a spatial representation *at all* in the brain. This fact is easily overlooked in normal perception where the percept of the world is easily confused for the world it represents, but it can no longer be ignored when half of that world disappears. Once we recognize the world of experience around us for what it really is, it becomes immediately obvious that the brain is capable of generating vivid three-dimensional spatial percepts that can rotate, translate, and scale by perspective as they move about in the perceived world. Once we accept this capability of the brain, a great host of otherwise deeply mysterious phenomena suddenly seem to make more sense, i.e. they no longer require heroic efforts of denial to account for their manifest properties. Those phenomena include hallucinations, dreams, mental images, neglect syndrome, the Kanizsa and Necker cube illusions, apparent motion phenomena, neon color spreading, etc. etc. These phenomena are now quantifiable in a perceptual model exactly as they are observed, and that model in turn sets a lower limit on the information that must be encoded in the corresponding neurophysiological state.

The criticism that my discussion of neglect is based on an "insufficient review of the actual phenomenon" suggests that the reviewer does not understand the paradigmatic nature of what is being proposed. I am not offering a specific computational model to account for all the properties of neglect syndrome, for that would require a whole paper devoted to that specialized topic. Instead, I am proposing that *if* spatial perception and mental imagery (in neglect syndrome or elsewhere) appear phenomenally as volumetric spatial structures, then that is how they are encoded explicitly in the brain.

...

Paradigm debates do not come around often in science, and when they do, they require a more general handling than the debates over details that characterize "normal science" as discussed by Kuhn. In the discussion section I touch on a great variety of different phenomena which have been deeply problematic for models of visual representation, but which can be addressed much more readily using the explicit spatial representation of the Gestalt Bubble model. My intent is not to address them individually here, but merely to suggest that they are ideal candidates for the perceptual modeling approach, for they are difficult to even describe in more abstracted terms. This intent is made clear in the concluding paragraph of the discussion section which states:

"It is perhaps too early to say definitively whether the model presented here can be formulated to address all of the phenomena outlined above. What is becoming increasingly clear however is the inadequacy of the conventional feed-forward abstraction approach to account for these phenomena, and that therefore novel and unconventional approaches to the problem should be given serious consideration."

End of section quoted from last response.

To elaborate on my previous response, if it is true that there is a dissociation between hemineglect in mental imagery and visual perception, as Coslett suggests, then it simply means that there must be two separate mechanisms for spatial perception and for spatial imagery. But they are *spatial* mechanisms nonetheless, and that is the message of the present paper. If I have a spatial experience either in perception or in mental imagery, then there must be a spatial representation in the brain corresponding to that experience. If it is true that the phenomenon of hemi-neglect "fractionates to a number of discrete patterns of impairment", then the perceptual system must be composed of discrete patterns of mechanism. However any aspect of the phenomenon which is spatial in nature, implicates a spatial representation to account for that particular aspect.

A "textbook-level general description" is *exactly* what is appropriate when presenting a general paradigmatic hypothesis whose focus is not on the details of any particular theory, but on the principles behind all such theories. The Gestalt Bubble model adds something very significant to traditional descriptions and explanations of neglect. It adds the very significant observation that *any* model of perception, mental imagery, or neglect syndrome, that postulates a spatial experience of any sort, in the absence of an explicit spatial representation with equal information content in the brain, is an **inadequate model of the phenomenon**.

3. visual phenomenology outside the focus of attention or eye fixation

it is unclear whether the model describes correctly all of our visual phenomenology. for example, before we focally attend to an object, and after attention has departed, there are only "preattentive object files" or "shapeless bundles of basic visual features" (e.g. wolfe & bennett 1997, vision research 37, 25-43). can the model account for this fuzzy phenomenology outside the focus of attention? also, outside the plane of depth where we currently fixate, we have double vision: when we fixate far, near objects appear in two and vice versa. what happens outside the plane of depth of fixation according to the bubble model? or does the model only account for visual phenomenology within the focus of attention? in that case it is not a model of the whole phenomenal visual field.
 

The Gestalt Bubble model does not "describe correctly *all* of our visual phenomenology". That is not the intent of the model! (I would love to see a model that fulfills that requirement!) The *only* aspect of visual phenomenology addressed by the Gestalt Bubble model is the aspect of *spatial perception*, i.e. the subjective experience of solid volumes, bounded by colored surfaces, embedded in a spatial void. This is an aspect which is pointedly ignored by many models out there, and therefore it is a topic of great significance to the debate.

If Wolfe & Bennett (and Dennett, and Pessoa et al, and O'Regan, etc.) can convince themselves that their un-attended vision consists of nothing more than "preattentive object files" or "shapeless bundles of basic visual features", that is not the world that *I* see in my un-attended vision. For although there is some considerable loss of resolution and spatial detail outside the focus of attention, the phenomenal world continues to appear as a volumetric spatial structure, rather than a shapeless bundle of visual features. The data of Wolfe & Bennett do not distinguish between these hypotheses. Now a *complete* model of phenomenal experience would have to include this phenomenon, filling in the spatial percept at high resolution wherever the focus of attention is directed, and allowing it to slump back into a less defined state in unattended regions. If vision is indeed double outside the plane of depth fixation, then that too is a property of phenomenal experience which would have to be incorporated into a *complete* model of vision. The Gestalt Bubble model is not intended as a complete model of all of these phenomena, it is more of a general principle of modeling presented here in its simplest form, but the same principle can be readily extended to address those more specific properties of perception in papers devoted to those specialized domains.

4. the ontological status of consciousness in the bubble model

the author makes it very clear that the bubble model is *epistemologically* committed to indirect realism. however, it remains unclear what the *ontology* of consciousness is according to the model.

the author refers to psychophysical parallelism and explicates his view in terms of a computer metaphor of how patterns of voltages inside the computer can represent meaningful information. he says that phenomenal experience is "a data structure", "pattern of energy in the physical brain", "pattern of activation", and that "we observe the information" (not the physical medium itself).

these characterizations suggest that the author endorses standard philosophical functionalism and representationalism about consciousness, as formulated and defended e.g. by tye (1995, ten problems of consciousness, mit). lehar certainly seems to say that we observe the *content* of information (or representation), not its physical *vehicle* in the brain.

the problem is that representationalists who build their theory on exactly that basis (e.g. tye, dretske), claim that phenomenal content is identical to representational or *intentional* content, and since intentional content is not in the brain, also phenomenology is not in the brain! thus, they are *externalists* as to the content of consciousness.

by contrast, lehar seems to deny externalism, but at the same time he seems to accept the distinction between the physical medium of information, and its content, and he says that his theory only concerns the latter. lehar should clarify to what extent he accepts standard representationalism (as defended by e.g. tye, 1995), because now he seems to accept some of its ideas while denying others, which makes it rather difficult to figure out what the metaphysical commitments of his theory are, or whether they even can be coherently formulated.

This is a good point, and would make an admirable subject for a philosophical paper in a philosophical journal (see Lehar 2000a and Lehar 2000b). But it goes beyond the scope of the intended focus of the Gestalt Bubble model. Already Reviewer #3 complains that
 

"It seems to me that the author is attempting to do "too much". On the one hand the author seems to engage in a philosophical battle with several century-old issues. At the same time, the author proposes a novel, original theory of space perception. It seems to me that the greatest contribution is by far the latter. The philosophical arguments should take part of background material, or discussion, but in a much more summarized manner. They serve to motivate his theory."

In case the reviewer should suspect that I have no answer to this objection, I will provide my answer here. It is, to my knowledge, a unique and original perspective on the problem which you will not find in Tye's book. In fact, despite his protestations to the contrary, Tye reveals himself to be a naive realist at his very core, along with the other "externalists" and "Token Physicalists" or "Functionalists", (Putnam 1968, 1975) and "Anomalous Monists" (Davidson 1970, 1980), and "Non-naturalists" or "Old Mysterians"(Popper & Eccles 1977, Adams 1987, Swinburne 1984) who suggest that phenomenology is located somewhere other than in the brain. For if it is not located in the brain, then where else could it possibly be? Phenomenal experience clearly has an information content, and information cannot exist independent of a physical medium to carry that information. Therefore phenomenal experience cannot simply exist in some abstract immaterial space, it must have a physical substrate, and that substrate is the brain. In other words the proponents of "Identity Theory" or "Type Physicalism" (Broad 1925, Feigl 1958) had it right all along. The mind is a dynamic physical process going on in the physical brain, fully visible in conscious experience, not some etherial abstract entity tucked away in some mysterious non-physical space. (It is extraordinary to what lengths otherwise intelligent people will go to attempt to rationalize their Naive Realist intuitions!) This does not however preclude the possibility that mind may be a manifestation of some hidden higher dimension of physical reality (Smythies 1989, 1994) or a macroscopic manifestation of some microscopic quantum effect (Crick & Koch 1990), although I don't believe this kind of elaborate hypothesis is really necessary to account for the observed properties of conscious experience (Lehar 1999). The Gestalt Bubble model also precludes the Eliminative Naturalist position (Churchland P. M. 1981, Churchland P. S. 1983) that seeks to quine consciousness altogether, as if the vivid spatial structure of consciousness simply did not exist. Nor does it allow the "Anti-Constructive Naturalist" or "New Mysterian" position (McGinn 1991) that suggests that consciousness is in principle beyond human comprehension. The Gestalt Bubble model already deflates that view by the observation that consciousness is (among other things) a colored spatial structure (a concept easily within human grasp), and that structure is explicitly present in the brain. In fact, Indirect Realism suggests that it is objective external reality which is forever beyond full human comprehension, not conscious experience, which is perhaps the *only* thing we can *ever* fully comprehend.

As for the vehicle v.s. content distinction, Information Theory can help to clarify that issue also. For information is defined independent of the physical medium by which it is carried. However in every case there must be some physical medium to carry that information. And the same principle also holds on the subjective side of the mind / brain barrier, where the information encoded in conscious experience is carried by modulations of some subjective quale, whether it be variations of hue, brightness, saturation, pitch, heat or cold, pleasure or pain, etc. For qualia are the carriers of the information experienced in perception (Rosenberg 1999), just as electromagnetic waves are the carriers of radio and television signals. Therefore the conscious qualia such as color and pain are the *vehicles* that carry the information in conscious experience, but the information itself is seen in the modulations of those qualia, i.e. the modulations are themselves the *content* of conscious experience. But the content cannot possibly be anywhere else than in the vehicle that carries them, just as the modulations of a television signal are located in the electromagnetic wave that carries them. In fact the Indirect Realist perspective eliminates the distinction between the neurophysiological "vehicle" and its phenomenal "contents", to show that they are not distinct entities, but merely different manifestations of the same underlying structure viewed from different perspectives.

I'm sure the above argument does not resolve this issue for this reviewer, I'm sure that the answer given above merely stimulates more questions for him, which could only be addressed fully in a paper devoted to this specialized topic. But that is exactly why this theory should be published, because it will be stimulating new questions like this one for decades to come.

References

Adams R. M. (1987) "Flavors, Colors, and God." In "The Virtue of Faith and Other Essays in Philosophical Theology." New York: Oxford University Press.

Broad C. D. (1925) "The Mind and Its Place In Nature." London: Routledge & Kegan Paul.

Churchland P. M. (1981) "Eliminative Materialism and the Propositional Attitudes." Journal of Philosophy 78, 67-90.

Churchland P. S. (1983) "Consciousness: The Transmutation of a Concept." Pacific Philosophical Quarterly 64, 80-93.

Davidson D. (1970) "Mental Events" Oxford: Oxford University Press.

Davidson D. (1980) "Essays on Actions and Events" Oxford: Oxford University Press.

Feigl H. (1958) "The Mental and the Physical." Minnesota Studies in the Philosophy of Science, Vol. 2. H. Feigl, G. Maxwell, & M. Scriven (Eds.) Minneapolis: University of Minnesota Press.

Lehar S. (1999) "Harmonic Resonance Theory: an Alternative to the `Neuron Doctrine' Paradigm of Neurocomputation to Address Gestalt properties of perception." Rejected Psychological Review November 1999. Available at http://cns-alumni.bu.edu/pub/slehar/webstuff/hr1/hr1.html

Lehar S. (2000a) "The Dimensions of Conscious Experience: A Quantitative Phenomenology". Journal of Consciousness Studies Rejected April 2001. Available at http://cns-alumni.bu.edu/pub/slehar/webstuff/consc/consc.html

Lehar S. (2000b) "The Function of Conscious Experience: An Analogical Paradigm for Perception and Behavior". Consciousness & Cognition (under review) Available at http://cns-alumni.bu.edu/pub/slehar/webstuff/consc1/consc1.html

Lehar S. (2001) "Directional Harmonic Theory: A Computational Gestalt Model to Account for Illusory Contour and Vertex Formation". Submitted Perception & Psychophysics, August 2001. Available at http://cns-alumni.bu.edu/pub/slehar/webstuff/dirhr/dirhr.html.

McGinn C. (1991) "The Problem of Consciousness." Oxford: Blackwell.

Popper K. & Eccles J. (1977) "The Self and Its Brain". New York: Springer-Verlag.

Putnam H. (1968) "Psychological Predicates" In Putnam H. (Ed.) Collected Papers II. Cambridge: Cambridge University Press.

Putnam H. (1975) "The Nature of Mental States" In Putnam H. (Ed.) Collected Papers II. Cambridge: Cambridge University Press.

Rosenberg G. H. (1999) "On the Intrinsic Nature of the Physical". In: S. R. Hameroff, A. W. Kaszniak, & A. C. Scott (Eds.) Toward a Science of Consciousness III the Third Tucson Discussions and Debates, Cambridge MA: MIT Press, pp 33-47.

Smythies J. R. (1989) "The Mind-Brain Problem." In: J. R. Smythies & J. Beloff (Eds) The Case For Dualism. Charlottesville: University of Virginia Press.

Smythies J. R. (1994) "The Walls of Plato's Cave: the science and philosophy of brain, consciousness, , and perception." Aldershot UK: Avebury.

Swinburne R. (1984) "Personal Identity: The Dualist Theory." In S. Shoemaker & R. Swinburne (Eds.) Oxford: Blackwell.

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Joint referees #2 Jonathan Opie & Gerard O'Brien ======================================================================
 

Note: This document is also avaliable on-line at http://cns-alumni.bu.edu/pub/slehar/webstuff/bubw/rebut2-0.html where hyper-links to additional source material are provided.

minor issues forgive us if some of these seem a little pedantic, but they are offered in a constructive spirit.

1. title. why use the definite article in the article's title ("...the subjective conscious experience...")? one is inclined to ask: "which subjective conscious experience?". surely, it is better to use "... the primacy of subjective conscious experience".
 

This is a question of emphasis. In this paper I emphasize that conscious experience is not some ethereal entity existing in some abstracted space, but it is a very real and solid physical entity that resides in the physical brain. Attaching the definite article to the subjective conscious experience serves to *objectify* the concept, to suggest that it is something concrete and real. As to *which* conscious experience, I can only report on the only one I know, which for me is indeed *THE* subjective conscious experience.

2. section 1, par.4 lehar's interpretation of contemporary materialism as "psychophysical parallelism" is wrong on two counts. first, contemporary materialist philosophers don't subscribe to this view, and second, psychophysical parallelism is really a form of dualism.

a better way of characterizing contemporary materialism is by reference to "token physicalism", which is general enough to subsume variants such as functionalism and the identity theory. lehar's "psychophysical parallelism" is a minority position in the contemporary philosophy of mind (sometimes ascribed to nagel and chalmers, for example). this is not intended as a criticism of the point lehar makes in the latter half of the paragraph, which we regard as important.
 

The term "psychophysical parallelism" has been removed from the new version.

3. section 2.2 lehar overstates the "incredible" nature of indirect realism when he claims that it flies "in the face of everything we know about neurophysiology". here lehar has not taken sufficient account of the recent work in neurocomputation (such as that of paul churchland and o'brien & opie) which explicitly aims to bring the phenomenology of conscious experience together with the details of neural network information processing. lehar should demonstrate a greater appreciation of this work. (see also 17. below.)
 

The response to this critique is included in the response to point 17 below.

I am making an emphatic point here on the *origins* of psychology, which was indeed defined originally as the science of the *psyche* [thus the name "*psyche*-ology"], i.e. the science of conscious experience. Now since behavior is also part of the conscious experience, it would naturally be included in the science of psychology. But then so would sensation, perception, and cognition, not to mention language, motivation, emotion, development, learning, memory, etc., which are all part of the conscious experience and therefore are properly part of psychology. However my intent is to focus here on the *original* thrust of the science of psychology, which was the investigation of the subjective conscious experience.

the expression "mind/brain barrier" which is used in several places, is also a bit problematic. if the mind is the brain, or a particular kind of activity of the brain, then it is not really apt to speak of a "barrier" (by analogy, presumably, with the blood-brain barrier). why not simply say "...the subjective side of the brain" or "the subjective aspect of brain activity" or simply "conscious experience"?
 

This is a stylistic issue, attempting to put additional emphasis on a particular concept for the sake of the argument. The word "barrier" denotes not only a physical barrier, as is the case with the blood-brain barrier, but there are also conceptual barriers. And there is indeed a formidable barrier between mind and brain. For although we can explore another person's brain in neurosurgery, we cannot ever directly explore the mind that resides inside that brain. Conversely, we can only see the world itself through the medium of our conscious experience. So we can never get in to another man's mind from the outside, and we can never get out of our own mind from the inside. This is as formidable a barrier as any that science has encountered.

The page reference has been provided.

6. section 2.4, par.3 is doesn't strike us as appropriate to describe the objects of experience as the "`product' or `output' of consciousness". these objects, understood as phenomenal objects (and not as the things in the world to which those phenomenal entitites refer) are among the *components* of conscious experience -- *part of* consciousness, not something consciousness *produces* (unless lehar thinks of consciousness as a process that produces a bunch of conscious experiences).
 

This is a stylistic turn of phrase chosen to make a particular point. In this case the point is to emphasize the reversal of information flow between direct v.s. indirect perception. The word "output" was isolated in protective "quotation marks" to indicate that it should not be interpreted literally, but figuratively, or metaphorically.
 

I am not aware of any paper that convincingly counters Chalmers' analysis, which in my view is both insightful and unimpeachable. Chalmers himself tells me that he has not heard any convincing counter-arguments. Furthermore, the reviewers themselves (O'Brien & Opie 1999 Section 5.4 "The Explanatory Gap") cite Chalmers to make the same essential point, *without* reference to the "large literature" supposedly refuting Chalmers' argument.

8. section 3, par.3 o'brien and opie's (1999) vehicle theory is a *connectionist* vehicle theory. thus, it aims to explain consciousness in terms of the vehicles of explicit representation as these are understood by connectionists. lehar gives the impression that this approach commits one to a naive first-order resemblance account of mental representation (a square shape in the world represented by a "square shaped region of activation in the brain"). no such commitment attaches to a vehicle theory. see the author's reply in the same issue.

The offending section has been removed from the paper.

9. section 4 in this section lehar initially claims that his perceptual modeling approach "avoids" and "sidesteps" the traditional philosophical problems inherent in neural models of perceptual experience. however, later in this section he admits that his approach really only "postpones" these problems. the former language is thus obviously too strong and should be toned down. (by the way, it is "nagel" not "nagle".)
 

Perceptual modeling does indeed "avoid" or "sidestep" philosophical problems inherent in neural models of perceptual experience, and it does so by not addressing the neurophysiological issues at all. Therefore the perceptual model is a *complete* solution to modeling perception, although it is only an *interim* solution to the larger *neurophysiological modeling* question. So I stand by the statement that the perceptual model avoids and sidesteps the philosophical problems. (The spelling error has been corrected.)

10. section 8, par.3 lehar says: "the extrinsic constraints are those defined by the visual stimulus, whereas the intrinsic constraints are those defined by the structure of the percept. the configuration of the input encodes the extrinsic constraints, while the stability of the perceptual representation encodes the intrinsic constraints."

wouldn't it be more appropriate to say that the structure of the percept is *determined by* constraints intrinsic to the computational mechanism. it doesn't really make sense to say that the intrinsic constraints are "defined" by the structure of the percept. rather, it is the former, however they might be physically implemented, that determine the latter. of course, the constraints are in some sense implicit in the final structure of the percept, but they aren't defined by it.
 

The suggested correction has been made in the new version.

The suggested correction has been made in the new version.

It is a common criticism that Gestalt theory fails to specify the higher order Gestalt principles like prägnanz and emergence in terms of a computational mechanism. Actually Wolfgang Köhler (1924) showed that there is no magic in emergence or prägnanz, they are common properties of certain kinds of physical systems, such as the soap bubble taking on its spherical shape, or water seeking its own level in a vessel. As Köhler pointed out, that equilibrium state tends to exhibit simple regular patterns, as seen in the spherical shape of the soap bubble, and the flat surface of water, and that simplicity of the equilibrium state is itself the property of prägnanz. So it is perfectly meaningful to talk of "the most stable configuration" and "the greatest simplicity or prägnanz", when talking about a dynamic system model. All that remains to be established is exactly what kind of dynamic system might be active in perception, and exactly how it might work.

The only valid criticism of Gestalt theory is its failure to provide that specific mechanism, not its failure to define the meaning of prägnanz. And to provide a specific mechanism behind visual perception is exactly the objective of the Gestalt Bubble model. In fact the real value of the Gestalt Bubble model is exactly that it offers one example of how a perceptual model can be built to exhibit the properties of emergence and prägnanz, with the final percept corresponding to the equilibrium state of the system. The objective of the Gestalt Bubble model therefore is exactly to provide "an explanation in terms of a computational mechanism" of the elusive Gestalt principle of prägnanz.

The mechanism which I explicitly avoid discussing in this paper is not the computational mechanism of perception, but rather the neurophysiological embodiment of that computational mechanism as expressed in the physical brain. In fact I have suggested exactly such a neurophysiological theory to account for the Gestalt properties of perception elsewhere (Lehar 1999). However in the present paper I have elected to confine the discussion to perceptual modeling issues, independent of neurophysiological considerations.

11. section 8.1 we think it would be appropriate at this point to reiterate that the neural implementation of the "volumetric block or dynamic computational elements" need not be a topographic or topological isomorph of this model, but need only be, in lehar's terms "functionally isomorphic". this will decrease the risk of mis-interpretation regarding the model.
 

In point 14 (below) the reviewers request clarification on the issue of structural v.s. functional isomorphism. In response to that request I have inserted additional explanation in section 5, including a new figure, to clarify this issue. That additional explanation obviates the need for a re-iteration here.

The reviewers seem to have missed the whole point. The curious aspect of size perception that demands explanation is the fact that distant objects are perceived to be both smaller (by perspective), and yet at the same time to be undiminished in size, as if size perception were a dual phenomenon, encoding simultaneously two different values for the perceived size of the perceived object.

The Gestalt Bubble model proposes a new and original explanation for this phenomenon in the form of a kind of double representation which incorporates that duality in the representation itself. Although distant objects are actually represented as smaller in this model (i.e. they occupy less space in the representational matrix itself) the scale of the representation also shrinks with distance from the egocentric point (i.e. the center of the perceptual sphere) so that although distant objects are smaller, they are measured against a shrunken reference grid, and therefore they are judged to be undiminished in size.

So this model handles "objective instructions" by measuring the size of percepts relative to the shrinking objective-size scale, and it also handles "projective instructions" by the actual size of percepts in the representational matrix.

13. section 10, final par. to speak of having "direct experience" of the "internal effigies" of objects in the world is rather odd. we understand lehar's point of course, namely, that our access to objects in the world is indirect, and mediated by internal perceptual states. even so, it would be better to say that our experience is comprised of internal effigies of objects in the world, rather than of the objects themselves.

There are some who claim that phenomenal experience is mediated by "the vehicles of explicit representation in the brain", but at the same time the experience itself corresponds to the *contents* of those vehicles, rather than the vehicles themselves. This kind of double explanation which has the vehicles as neurophysiological entities, but their contents as subjective phenomena, invites the dualistic interpretation that leaves unanswered the question of how the vehicles are related to their contents. The language chosen above, by contrast, emphasizes the unity of the subjective experience and the corresponding neurophysiological mechanism in the brain. They are different aspects of the same underlying structure, viewed from the internal subjective context v.s. the external objective context. Therefore there is no ontological difference between the "vehicle" and its "contents", they are one and the same thing. The Gestalt principle of isomorphism highlights this unity, because the isomorphism is not some incidental quality that compels the subjective and objective percepts to conform to each other, but rather they cannot help but be isomorphic, because they are different manifestations of the same essential structure, viewed from two different perspectives. I stand by the statement that the internal effigies in perception are directly experienced.

But forget the subjective experience for the moment: In the case of the photo (vehicle) and the object that it is a photo of (content) the isomorphism between the properties of the vehicle (photo of an apple) and its content (the apple) are obvious and unproblematic. This does not carry over, however, unproblematically, to whatever the vehicle of a conscious experience might be, for the simple reason that apples can be round, photos of apples can be round, maybe even neural structures can be round, but it is is not at all clear how what it feels-like to experience something as round can be round.

This is the vehicle/content problem, and you cannot wave it away quite this easily.

major issues below are some issues which we consider to be of greater significance.

14. section 6.1 this section is quite problematic. having gone to considerable trouble to establish that the model being presented does not directly bear on the neurophysiological correlates of conscious experience, but merely codifies or systematises the information content and structure of consciousness, lehar here raises what appear to be problems for a theory of the neural correlates.

the reply to the homunculus problem is fine, as far as it goes. lehar rightly notes that this is just as much a problem for a symbolic conception of mental representation as for an analog conception, but is in fact no problem at all, because the threatened regress can be contained by assuming mental processes that are sensitive to the symbolic or analog structure of the representations.

the trouble is, lehar in effect admits here that his theory is (to some extent) a theory of the neural vehicles of consciousness. he describes them as "full spatial analog[s]" of the environment and "explicit spatial representation[s]". those assertions appear to speak to the nature of the vehicles, rather than their contents.

to make matters worse, in the latter part of the paragraph lehar reverts to talking about the contents of the vehicles in defense of his view. he says that the "existence and fully spatial nature [of percepts] in my internal perceptual world is beyond question". this is surely a claim about the contents of visual experience.

talk of "explicit spatial representation" and "spatial nature of the perceptual representation" now becomes quite ambiguous. is it the vehicles that are spatial (and hence topologically isomorphic with what they represent), or do they merely *represent* spatial properties.

Ed: To show that editorial judgment is neither a box-score nor a literalist acceptance of everything the referees say, "represent" here is a weasel-word (and I wish the referee had not used it). The issue here is consciously experiencing spatial properties, not merely "representating," or having an "internal representation of" them. A photo represents. But a photo does not feel. It is hence unclear, to say the least, how or why having a photo in the head should feel like anything either.

So never mind the equivocal language of "representation." If you are indeed trying to explain qualitative experience and not merely quantitative input/output performance, you have to face the problem of the incommensurability between, on the one hand, the properties of vehicles (like photos of apples) plus their contents (apples), and, on the other hand, what it feels like (e.g. to see an apple). It makes no difference whether the photos are on paper or in your head, and no difference whether there is an isomorphism between properties of the photos and properties of the apples that they are the photos of. The problem is the nature of the "morphism" between all of that and the properties of felt experience: Not the vehicles of felt experience, which might well-be photo-like, but the properties of felt experience.

No fancy theories needed for this. Enough to ask: What (other than correlation) does what roundness feels-like have to do with what roundness is (whether in the neurophoto, the external photo, or the apple)?

Some sorting out and clarification needs to be done here. Lehar will have to SHOW HOW TALK OF "SPATIAL ANALOGS" IS CONSISTENT WITH HIS EARLIER INSISTENCE ON FUNCTIONAL ISOMORPHISM, as opposed to structural or topographic isomorphism. And he will have to SHOW HOW TALK OF "EXPLICIT SPATIAL REPRESENTATION" IS CONSISTENT WITH HIS CLAIM TO HAVE SIDESTEPPED "THE PROBLEMS OF EXPLICIT V. IMPLICIT REPRESENTATION" (Section 4, Par.2).

[Note: CAPS above indicate sections highlighted by the editor for particular importance to address.]
 

A whole new section has been added to section 5 in the paper, clarifying the relation between structural and functional isomorphism, complete with the new Figure 1 to illustrate the concept. I suspect these reviewers will be unhappy with this explanation, as it highlights the fact that I do indeed advocate a "Picture-In-The-Head" theory of spatial representation, a position that they argue against in their own paper.

O'Brien & Opie (1999) argue that "We don't expect the green of grass to be represented by green-colored neural vehicles. Why, therefore, should we expect spatial properties of the world to be represented by corresponding spatial properties of the brain?"

But if "greenness" is not a property of the brain, where does that green color come from? It cannot be a property of the world itself, because it is a subjective quale, i.e. a kind of arbitrary mapping used in the internal representation of the brain to represent light of median wavelengths. The green color is itself a property of the physical mechanism of the brain, not of the external world. Although the neurophysiological correlate of this green quale has yet to be identified, we already know for a fact that it is green, because we can see it "from the inside". That does not mean it will look green to an electrode that measures the activation of particular cells in the brain, nor that those cells would appear green under microscopic examination. The greenness can only be experienced internally, but that does not make it any the less green, or any the less a characteristic quality of certain physical processes in the physical brain.

I have edited BBS for 25 years. I never reqire authors to agree with me, or with the referees. All I insist on is that substantive criticisms should be understood, acknowledged, faced, and taken explicitly into account. I don't want a nonsequitur on this hoary problem in your target article. You can of course stick to the view you would like to recommend, of the nature of internal representation. But you must show that you have understood the point about the vehicle/content distinction, and its bearing on the (apparent) problem of the incommensurability between physical properties (spatial or otherwise) and felt qualities, and its bearing on any "isomorphism" view.

On the question of the spatial properties of the phenomenal world, if the representation subserving that phenomenal experience is *not* itself spatial, then why would it appear spatial phenomenally?

There are many non-spatial ways to represent spatial information. For example it can be expressed in the form of mathematical equations that describe spatial structures, or spatial structures can be expressed in a Fourier code. But if our brain were to employ either mathematical equations, or Fourier descriptors as its representation of spatial structure, then our subjective experience would itself necessarily appear in the form of mathematical equations, or of Fourier descriptors. The fact that the world of experience takes the form of a spatial structure is direct evidence for a spatial representation in the brain.

I do not expect the reviewers to be convinced by this argument, this is a central paradigmatic issue around which the whole paper revolves. It is the inevitable consequence of taking an Indirect Realist view of perception, which shows that the properties of the phenomenal world are properties of the brain first and foremost, and only in secondary fashion are those properties also reflective of certain properties of the external world. It is curious that O'Brien & Opie join Atkins (1996) in calling Isomorphism a "Naive Theory of Perception". In fact it is their own view which is the one consistent with Naive Realism, because they seem to accept without question that the world appears spatial, although they deny a spatial representation in the brain, as if we were viewing the world directly, instead of by way of the medium of the representational mechanism in the brain.

If, at the end of the day, Lehar does subscribe to a "PICTURE-IN-THE-HEAD" APPROACH to visual perception, he MUST DO MORE TO DEFEND IT AGAINST THE NUMEROUS OBJECTIONS IT FACES. There is A VOLUMINOUS PSYCHOLOGICAL/ PHILOSOPHICAL LITERATURE ON THIS PROBLEM, with which Lehar should show at least some familiarity. A good place to go, for example, is the volume "IMAGERY" EDITED BY NED BLOCK. Of particular interest to Lehar will BE FODOR'S WELL- KNOWN REPLY to the "infinite regress of observers within observers" criticism that Lehar ascribes to Dennett, O'Regan and Pessoa et al.

[Note: CAPS above indicate sections highlighted by the editor for particular importance to address.]
 

As far as I can tell, the "numerous objections" faced by the Picture-In-The-Head theory amount to one single objection, and that is the tired-old homunculus argument, which has already been dispatched many times over. This is the worst kind of critique to receive in a review because it is so open-ended, it is hard to address. If there really *were* so many objections, why don't the reviewers mention one or two of them so I would know what they are talking about? I understand that the reviewers may *think* that there are numerous objections, but that is only because this alternative is so rarely given any serious consideration that the reviewers haven't heard it defended before. The reviewers casually point me to Ned Block's "Imagery". But that book contains **eight different articles by eight different sets of authors!** Any hint as to *which* of these authors supposedly delivers the coup-de-grace for the Picture-In-The-Head hypothesis? Or do I have to go through the entire book to address this reviewers objection?

Ned Block himself offers the answer right in the introduction, on page 2:

"But no one writing in this book (nor any other serious participants in the debate) thinks that people can literally see and manipulate real internal pictures. Brain scientists have found no pictures in the brain, and even if they had, the presence of pictures wouldn't explain the phenomena unless the brain contained an internal eye to view them and an internal flashlight and internal hands to manipulate them etc. (And even if we postulate an internal eye, would there still be another eye in that eye's brain? So we have a problem: the obvious explanation is blocked."

So the "formidable objection" by Ned Block is nothing more than the tired old homunculus argument! Block does however explain *why* this alternative seems so incredible, and that is because "brain scientists have found no pictures in the brain". This either means that there are no pictures in the brain, or that modern neuroscience is in a state of serious crisis, because it cannot find the pictures in the brain that we know must be there. And the evidence for the presence of those pictures is right before our eyes, if only we can see beyond the naive realist illusion and recognize the phenomenal world for what it really is.
 

It is not a solution to the hard problem to say: Put something in the head that is isomporphic with the feeling.

Chapter 1, by Roger Brown & Richard Herrnsteinoffers no arguments against the Picture-In-The-Head hypothesis.

Chapter 2, by Daniel Dennett, offers the following objection: (page 52)
 

"For an image to work as an image there must be a person (or an analogue of a person) to see or observe it ... we shall have to design a perceiver- analogue to sit in front of the image, and yet another to sit in front of the image which is the end product of perception in the perceiver-analogue, and so forth ad infinitum."

So its the tired old homunculus argument being dragged out again! On page 56 Dennett discusses the question of hallucinations, and the phenomenal space in which they are observed, using the example of a "freak" visual experience caused by electrical stimulation of the cortex...
 

"Having a visual hallucination is ... just being aware of the content of a non- veridical visual `report' caused by such a freak discharge. And where is this report and what space does it exist in? It is in the brain and exists in the space taken up by whatever event it is that has this non-veridical content, just as my description of hallucinations takes up a certain amount of space on paper. Since spatiality is irrelevant to descriptions, freak descriptions do not require ghostly spaces to exist in.

If the neurophysiological "description" of the hallucination is not expressed as a spatial pattern in a spatial medium, what is it that transforms the phenomenal correlate of that description into the spatial pattern that we experience? How did phenomenal experience settle on a spatial format for presenting the non-spatial information in the brain? Why would it not, for example, appear phenomenally as a Fourier descriptor, or as a mathematical formula? And where does the transformation from non-spatial to spatial take place if not in the brain? And what is the algorithm of that transformation? And where is the spatial percept stored or registered? In truth, the fact that the phenomenal world appears as a spatial pattern is direct evidence for a spatial representation in the brain.

In Chapter 3 page 63 Jerrry Fodor offers his own "fatal blow" to the Picture-In-The- Head theory by announcing that he is...

"unsympathetic about the empirical basis for the existence of stagelike changes in modes of internal representation ... because I think it would be appalling if the data really did somehow require us to endorse that kind of view. I am, in fact, strongly inclined to doubt the very *intelligibility* of the suggestion that there is a stage at which cognitive processes are carried out in a medium that is fundamentally nondiscursive."

So Fodor's whole argument is that he finds the idea incredible! He then goes on to present a caricature of a simplistic image-based "language" which he calls "Iconic English", and demonstrates how this simplistic concept is inadequate as a model of thought. For example if "John" is represented by an image of John, and "green" is represented by a green tile, then the sentence "John is green" could not be meaningfully constructed out of those elements. So Fodor succeeds in shooting down his simplistic straw man theory of imagistic thought, and thereby supposes he has put an end to the notion altogether.

Chapter 4 is written again by Daniel Dennett. This time he "defeats" the notion of mental imagery by constructing a fanciful analogy. He asks the reader to imagine that anthropologists have discovered a native tribe that believes in a hitherto unheard-of God of the forest, named "Feenoman" (this will stand in for the supposedly fictitious "phenomenal experience" whose existence Dennett so forcefully denies). Some of the anthropologists begin to believe in Feenoman as an objectively real deity (the "Feenomanists"), while others retain their scientific rigor, and study the native religion while remaining agnostic themselves (the "Feenomanologists"). On page 102 Dennett concludes that:
 

"Phenomenal space is Mental Image Heaven ... [mental images] can reside, with Santa Claus, in the logical space of fiction."

But analogies only work when the analogy is analogous. In this case nobody has ever actually seen Feenoman, and therefore it is reasonable to question His existence. The phenomenal world on the other hand is right before our eyes, if only we can recognize it for what it is. Dennett's argument works better against mental imagery than perception, because it is easier to deny the existence of those...
 

"...entirely mythical species of mental images: the various non-physical, phenomenal or epiphenomenal, self-intimating, transparent to cognition, unmisapprehensible, pseudo-extended, quasi-imagistic phantasms that have often been presented as mental images in the past." (page 104)

However this argument does not work so well against perception. For to deny a spatial representation in the brain is to deny the vivid spatial structure so plainly evident in the world we see around us.

Chapter 5 is provided by Robert Schwartz, who launches into a minute analysis of exactly what images might be, and by what principles they differ from other forms of representation. His only serious challenge to the Picture-In-The-Head theory is his complaint that the concept of isomorphism is too vague, because it uses the concept of "similarity" between the picture and the object it represents. But since similarity is itself a rather vague term, Schwartz objects that

"the unqualified claim that a picture resembles its referent is vacuous."

Does Schwartz suggest that *any* statement about the similarity between items is also *vacuous*? Surely scientific discourse can meaningfully employ terms such as similarity even in the absence of a rigorous definition. In any case this objection is only valid when the claim is unqualified. In my own discussion of isomorphism I have qualified the concept of similarity by invoking *information theory*, and specifying that the *information content* of the subjective experience cannot be any greater than the information content of the corresponding neurophysiological state. The use of information theory to quantify the otherwise vague notion of similarity is a significant and original formulation of the issue of isomorphism, and this one step makes my own discussion of isomorphism impervious to many of the objections raised against this much-maligned notion.

Chapter 6 is provided by Kosslyn, Pinker, Smith, & Schwartz. As mental imagery advocates they offer no challenge to the Picture-In-The-Head hypothesis.

Chapter 7 is contributed by Zenon Pylyshyn, who is an ardent opponent of mental imagery. His argument is that what people report as properties of images, are actually properties of the objects they represent, not of the images themselves. For example when a mental image of a table is observed to have spatial extent, Pylyshyn argues that spatial extent is not a property of the mental image, it is a property of the table itself. Only a Naive Realist could possibly accept this argument because an Indirect Realist realizes that none of the properties of the objective external world can possibly penetrate into conscious experience except by way of explicit representations of them in the brain, mediated by sensory input. If the mental image did not have spatial extent, then no spatial extent would be experienced for that image. Pylyshyn argues as if the quality of spatial extent can somehow bypass the sensory interface to the world and penetrate directly into the experience of the imaging subject, without leaving an impression in the subject's brain.

The final chapter, Chapter 8, is written again by Stephen Kosslyn, who as a strong advocate of mental imagery offers no argument against the Picture-In-The-Head theory. However he does hazard to say on page 207 that

"Although no serious researcher today maintains that images are actual pictures in the head, some still find it reasonable to posit quasi-pictorial representations that are supported by a medium that mimics a coordinate space."

I find this statement puzzling, since the notion of quasi-pictorial representations supported by a medium that mimics a coordinate space is exactly what *I* consider to be "actual pictures in the head". So I am at a loss as to whether I am in agreement or disagreement with Kosslyin on this point. But in any case he offers no explanation for *why* no serious researcher believes in pictures in the head.

So, after poring through the "voluminous literature" in the recommended tome, all I have come up with is the homunculus argument! This is what I really hate about these journal reviews. At the casual mention of a "voluminous literature" and a vague pointer at a book, the humble supplicant for publication has to rush off to the library and plough through a mass of irrelevant material only to find that the reviewers did not know what they were talking about! I can understand why they may have had the *impression* that this book contained "numerous objections" to the notion, and that is because the notion was never even considered as a serious alternative by any of the parties to the debate. But that is all the more reason why it deserves that consideration now.

Daniel Dennett makes the insightful observation that although this issue remains unresolved, and that nobody really knows with any certainty whether there are pictures in the brain, (page 30)...

"A curious feature of the debate is the passion it evokes, which is unlike the normal passion of scientific controversy ... everyone, it seems, has a fiercely confident opinion about the nature and existence of mental images. This manifests itself in remarkable ways: in unhesitating predictions of the results of novel psychological experiments, in flat disbelief in the integrity of recalcitrant experiments, in gleeful citation of "supporting" experimental evidence, coupled with bland imperviousness to contrary evidence."

 

In his summary of the debate to date, Kosslyn et al. offer the observation that...

"Not surprisingly neither arguments nor counter-arguments have been definitive, and neither seems to have had enough force to sway most people from whatever position they found most congenial in the first place."

THIS IS A SURE SIGN OF A PARADIGMATIC DEBATE. The reason for the supreme confidence of the opposing camps is that they are not debating the facts of the case, as they would in a debate over more specific theories. Instead, the issue involves the paradigmatic question of whether the subjective conscious experience is a valid source of evidence for the nature of the neurophysiological representation employed in the brain.
 

 
For if it is, then the existence of mental images can be easily confirmed by inspection. And that choice in turn depends on the epistemological question of whether the world we see around us is the real world itself, or whether it is merely a replica of that world in an internal representation. The only way to break the endless cycle of fruitless debate is to cut through to the paradigmatic issue hidden at the core of the debate, and settle once and for all the question of the epistemology of conscious experience. The fact that *none* of the contributing authors in Ned Block's book even considered a Picture-In-The- Head theory even as a theoretical possibility, and the fact that the homunculus objection crops up so often without challenge, highlights the urgent need for this paper to be published without further unnecessary delay.

15. Section 6.2, Section 8.6 Same problem. WHAT DOES "LITERAL VOLUMETRIC REPLICA OF THE WORLD MEAN"? This talk HAS TO BE MADE CONSISTENT WITH THE ASSUMPTION OF FUNCTIONAL ISOMORPHISM.

[Note: CAPS above indicate sections highlighted by the editor for particular importance to address.]

This issue is now clarified in the new extended Section 5 in the paper.

16. Section 8.6 Again, Lehar says "The most significant feature of this concept of perceptual processing is that the result of the computation is expressed not in the form of abstract variables encoding the depth and slope of the perceived rectangle, but in the form of an explicit three-dimensional replica of the surface as it is perceived to exist in the world." ARE WE TO TAKE THIS LITERALLY? OR IS THE "REPLICA" HERE SOME KIND OF FUNCTIONAL ONE?
 

This issue is now clarified in the new extended Section 5 in the paper.

17.On PDP models.

In Section 9 Lehar claims that "the computational transformations observed phenomenologically are implausible in terms of contemporary concepts of neurocomputation and even in terms of computer algorithms".

In view of the VERY LIMITED DISCUSSION OF CONTEMPORARY COMPUTATIONAL APPROACHES TO CONSCIOUSNESS, AND TO GESTALT PHENOMENA in particular, THIS CLAIM HAS HARDLY BEEN ESTABLISHED.

Even so we grant that there is some prima facie plausibility to Lehar's claims where "neuron doctrine" style theories are concerned. We are not so convinced when it comes to PDP approaches. Indeed, we would offer the suggestion that the PDP APPROACH TO NEURAL COMPUTATION, SUITABLY INTERPRETED, HOLDS OUT SOME HOPE OF *IMPLEMENTING* THE VERY PERCEPTUAL MODEL LEHAR DEFENDS.

The PDP approach takes seriously the intrinsic structural properties of the brain, and attempts to develop an account of both cognition and perception consistent with these properties. It identifies as a principal computational mechanism a style of processing known as relation search (or constraint satisfaction). This, we suggest, is just the kind of mechanism required to implement the kinds of dynamic, reciprocal interactions, and emergent phenomena that Lehar postulates in sections 8.2, 8.3, 8.4, 8.5 and 8.6. We think Lehar might consider this suggestion, and, at the very least, MAKE SOME COMMENT AS TO THE POTENTIAL OF THE PDP APPROACH to implement his perceptual model.

18. On originality. This follows from the previous point. We accept that PDP theorists haven't said much about the representation of space, but there have been some tentative steps in the direction of applying PDP thinking to gestalt perceptual phenomena. We commend the following papers to the author:

PALMER, S.E. (1992) Modern theories of Gestalt perception. In: G.W.Humphreys (ed.) Understanding Vision. Blackwell. (See particularly the latter part of the paper.)

READ, S.J., VANMAN, E.J. & MILLER, L.C. (1997) Connectionism, Parallel Constraint Satisfaction Processes, and Gestalt Principles: (Re)Introducing Cognitive Dynamics to Social Psychology. PERSONALITY AND SOCIAL PSYCHOLOGY REVIEW Vol.1(1):26- 53 (Not focussed on perception, but a nice discussion of PDP and gestalt theory).

OPIE, J. (1999) Gestalt theories of cognitive representation and processing. Psycoloquy 10(021) http://www.cogsci.soton.ac.uk/psyc- bin/newpsy?10.021

[Note: CAPS above indicate sections highlighted by the editor for particular importance to address.]

The reviewers are obviously advocates of PDP models and therefore naturally reluctant to accept the limitations of their paradigm without specific proof that it is wrong. But it is impossible to prove a negative- i.e. I cannot demonstrate that no possible future PDP model could ever be formulated to address the Gestalt phenomena discussed in the paper. The onus is on the PDP advocates themselves to demonstrate the capabilities of their paradigm. However there is good reason to believe that the neural network paradigm has some serious limitations with respect to the phenomena specifically addressed by the Gestalt Bubble model.

The Gestalt Bubble model was formulated as a perceptual model, but the computational functionality that it performs can be readily expressed in PDP terms. However the result is a combinatorial explosion of receptive fields so great as to seem completely implausible to the author. That is why I chose to present it as a perceptual model rather than a neural network model, and that is why I stand by my statement that "the computational transformations observed phenomenologically are implausible in terms of contemporary concepts of neurocomputation". Now this is admittedly a personal judgement, as plausibility judgements necessarily are, so I cannot prove definitively that PDP models are implausible. But there is good reason to believe that they are implausible *for the class of perceptual computation* addressed by the Gestalt Bubble Model.

The reviewers point out correctly that PDP models of Gestalt phenomena have been proposed, that exhibit the Gestalt properties of emergence and prägnanz. That's all well and good, but those models happen to be irrelevant to the specific perceptual phenomena addressed by the Gestalt Bubble model, i.e. the perceptual transformation from a two-dimensional stimulus to a three-dimensional volumetric perceptual structure.

In fact some of the models the reviewers cite actually highlight the limitations of the PDP approach by the parts of the problem which they pointedly *avoid* addressing. For example Palmer (1990 p. 316) presents a PDP model to account for the ambiguous percept of an equilateral triangle as an arrow pointing in one of the three directions indicated by its corners. Palmer presents a simple dynamic neural network model in the form of three nodes with mutually inhibitory connections, resulting in a winner- take-all behavior. The activation of the winning node represents a percept of the triangle as an arrow pointing in the corresponding direction. This is an excellent demonstration of Gestalt dynamics in a perceptual model. But now consider what kind of architecture would be required to make those three nodes operate as advertised in response to a given visual stimulus. For it is here at the lower end of the visual hierarchy that neural network theory runs into a combinatorial mess. Let us begin with a functional description of what that processing must do. We need a circuit which can read a visual image, and identify the presence of one or more equilateral triangles in the stimulus. For each equilateral triangle the system must set up a triangle of mutually inhibitory nodes with dynamic behavior as described by Palmer. Forget the rest of the problem, like the question of how the final activation of the winning node for each triangle becomes a percept of a directed arrow. Even the computational functionality outlined above already poses a formidable challenge for PDP theories. We know how to make edge detectors out of neurons with spatial receptive fields, so we begin with edge detectors at every location across the visual field, replicated at every orientation. But the next problem of finding the triangles already begins to leap into combinatorial territory. For we now need "angle detectors" tuned to respond to pairs of lower-level edge detectors spanning a 60 degree angle. Like the edge detectors themselves, the angle detectors must be replicated at every location across the visual field, where they are also replicated at every possible orientation, and wired to the appropriate pair of edge detector cells. There are several ways to proceed from this point, but all of them are ugly. We could now posit "triangle detectors" tuned to respond to the presence of three "angle features" in a triangular configuration. These "triangle detectors" would also have to be replicated at every location across the visual field, at every orientation, and through a range of spatial scales, so as to be able to detect triangles independent of their rotation, translation, and scale. We could then equip each of these innumerable triangle detectors with the three nodes of Palmer's circuit to perform the competition between perceptual interpretations. If the reviewers do not find this architecture already completely implausible, consider the problem of generalizing the model to detect other types of triangles besided equilateral triangles, or other shapes such as squares or rectangles, each of which would require a whole different combinatorial set of feature detectors for each different shape!

There are neural network models out there which address lower level visual processing in Gestalt terms, for example Grossberg & Mingolla (1985, 1987) and Zucker et al. (1989). But these models themselves run headlong into the combinatorial problem as soon as they dare to tread beyond simple collinear completion. Zucker et al. (1989) posit curvature detectors at every location, orientation, and through a range of curvatures across the visual field. Grossberg & Mingolla (1987) briefly court with the idea of cells with receptive fields configured to respond to right-angled corners in the stimulus. But no mention is made of the combinatorial explosion hidden in that pandora's box, because explicit curvature or corner detectors suggest also detectors for other detectable features, such as acute and obtuse angle detectors, not to mention detectors tuned to vertex types composed of more than two edges, for example "T" or "Y" or "X" vertex detectors. For each of those specialized detectors would also have to be replicated at every location, orientation, and through a range of spatial scales across the visual field. Note that this is a problem not only with "feature detector" or "grandmother cell" models of visual representation, for the models of Grossberg & Mingolla, and of Zucker et al. are specifically *dynamic neural network* models, i.e. models that employ dynamic patterns of activation across the neural substrate to encode perceptual structure. But all those different receptive field types are still required just to control or channel the patterns of activation required for the functionality of the model, as I explain in detail in Lehar (2001). And the Gestalt Bubble model extends the required functionality into three dimensions, requiring three- dimensional volumetric receptive fields replicated at every location in three dimensions, and at every orientation in three dimensions and through a range of spatial scales.

I have explained elsewhere (Lehar 1999, 2001) that the Achilles heel of neural network theory lies in the principle by which it encodes spatial structure, i.e. the neural receptive field that is anchored to the tissue of the brain. For the receptive field is no different than a template theory, a concept whose limitations are well known. And yet this idea is so deeply entrenched in contemporary neuroscience that it will take a profound paradigmatic revolution to uproot it.

But it is impossible to prove a negative- plausibility arguments are necessarily based on intuitive appeal, or on the perceived promise (or lack of it!) of a theoretical approach which has not yet been fully demonstrated. So I do not expect the reviewers to be convinced by this plausibility argument, because the plausibility issue cannot be resolved definitively by argument and evidence alone. And that is why I felt that a discussion of the limitations of neural network theory would only distract from the principal message of the paper, which is not on the limitations of the older paradigm, but on the promise of the new one.

To conclude, let us reiterate that we think this is an insightful and valuable paper. We look forward to seeing it in print.

I would like to see how these reviewers review a paper they do *not* like!

References

Atkins K. (1996) Lost the Plot? Reconstructing Dennett's Multiple Drafts Theory of Consciousness. Mind & Language 11, 1-43.

Grossberg, Stephen, & Mingolla, Ennio (1985). Neural Dynamics of Form Perception: Boundary Completion, Illusory Figures, and Neon Color Spreading. Psychological Review, 92, 173-211.

Grossberg, Stephen, & Mingolla, Ennio (1987). Neural Dynamics of Surface Perception: Boundary Webs, Illuminants, and Shape-from-Shading.. Computer Vision, Graphics and Image Processing, 37, 116-165.

Grossberg, Stephen, & Todorovic, Dejan (1988). Neural Dynamics of 1-D and 2-D Brightness Perception: A Unified Model of Classical and Recent Phenomena" Perception and Psychophysics 43, 241-277.

Köhler W. (1924) Die Physischen Gestalten in Ruhe und im stationären Zustand: Eine naturphilosophische Untersuchung. Erlangen: Verlag der Philosophichen Akademie.

Lehar S. (1999) "Harmonic Resonance Theory: an Alternative to the `Neuron Doctrine' Paradigm of Neurocomputation to Address Gestalt properties of perception." Rejected Psychological Review November 1999. Resubmitted to Behavioral & Brain Sciences- not accepted for review because only one paper allowed per customer at a time (!) Available at

http://cns-alumni.bu.edu/pub/slehar/webstuff/hr1/hr1.html

Lehar S. (2001) "Directional Harmonic Theory: A Computational Gestalt Model to Account for Illusory Contour and Vertex Formation". Submitted Perception & Psychophysics, August 2001. Also available at

http://cns-alumni.bu.edu/pub/slehar/webstuff/dirhr/dirhr.html

O'Brien G. & Opie J (1999) A Connectionist Theory of Phenomenal Experience. Behavioral & Brain Sciences 22, 127-148.

Palmer S. E. (1990) Modern Theories of Gestalt Perception. Mind & Language 5 (4) 289-323)

Zucker, S. W., Dobbins, A.& Iverson, L. (1989). Two Stages Of Curve Detection Suggest Two Styles Of Visual Computation. Neural Computation, 1, 68-81

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Referee #3 anon
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Note: This document is also available on-line at http://cns-alumni.bu.edu/pub/slehar/webstuff/bubw/rebut2-0.html where hyper-links to additional source material are provided.

The present article is quite a difficult one to review. I suspect that referees with expertise in Philosophy have already been contacted, but I would strongly encourage you to contact experts in space/form perception, such as Jan Konderink, James Todd, or Ennio Mingolla. Researchers in these fields could more adequately evaluate the theory advanced by the author. I provide my own review below.

Lehar's manuscript has great potential to become a BBS target article. IN IT'S PRESENT FORM, HOWEVER, I FIND IT INADEQUATE for publication. Below I outline some of the reasons.

It seems to me that the author is attempting to do "too much". On the one hand the author seems to engage in a philosophical battle with several century-old issues. At the same time, the author proposes a novel, original theory of space perception. It seems to me that the greatest contribution is by far the latter. The philosophical arguments should take part of background material, or discussion, but in a much more summarized manner. They serve to motivate his theory. I find the present "AGGRESSIVE TONE" INADEQUATE, AND TO BE FRANK, NOT VERY PERSUASIVE.

[Note: CAPS above indicate sections highlighted by the editor for particular importance to address.]
 

Much of the philosophical discussion to which this reviewer objects was originally not part of the paper, and was added by demand of Reviewer #1 in the first round of review. I agree with this criticism, consequently I have removed some of that added material.

As for the "aggressive tone" which this reviewer finds "unpersuasive", this is an attitude I have developed as a consequence of a series of encounters with reviewers like this one. He says he is "not persuaded" but does not bother to explain of WHAT he is not persuaded, or WHICH arguments specifically he found unpersuasive, and exactly WHY they failed to persuade.

Perhaps it is the philosophical discussion which makes him so uncomfortable, because it forces the reader to make a choice between three incredible alternatives. The "aggressive tone" emphasizes the fact that this is a choice which cannot be conveniently avoided, because rejecting one alternative simply commits one to one of the remaining incredible alternatives. In my discussions with colleagues I have discovered that many feel very uneasy about having to make this choice, and would prefer to just avoid the issue altogether. The reviewer does not give us the benefit of his own thoughts as to whether it is Indirect Realism of which he remains unconvinced, or whether he is unconvinced of the validity of the argument which forces him to a choice in the first place. Unless he informs us otherwise, we can only guess at his motivations. But given the abundance of closet Naive Realists out there, the most likely explanation is that this reviewer is a Naive Realist at heart, his whole career has been committed to theories based implicitly on Naive Realist assumptions, and he feels uncomfortable at now being challenged to defend the indefensible. Like many psychologists this reviewer probably considers philosophical debates to be outside of his specialty, and therefore irrelevant to his branch of psychology. This is exactly why an "aggressive tone" is needed to wake these people up to the fact that psychology cannot be so neatly compartmentally insulated from philosophy, because every science is built upon a foundation of philosophical assumptions, and those assumptions are not always "testable" by the normal rules of evidence. Paradigmatic choices require the exercise of a kind of broad-minded judgement or intuition, which this reviewer probably considers to be unscientific.

And yet the choice must be made, because scientific theories which are built upon the wrong paradigmatic foundations are like castles built on sand, impervious to assault on the grounds of theory and evidence, but vulnerable to a blow below the paradigmatic belt. Given this reviewer's reluctance to share with us the reasons for his discomfiture, we can only guess what is motivations might be. But even if I have this reviewer's motivations all wrong, there are many more closet Naive Realists out there who are in need of an "aggressive tone" to wake them up to their responsibility as scientists to justify the foundations of their theoretical stance.

An EXPLICIT SECTION ON HOW THE MODEL DEALS WITH IMPORTANT FINDINGS IN THE PSYCHOPHYSICS OF FORM PERCEPTION IS REQUIRED. I find THE PRESENT DISCUSSION SECTION INADEQUATE. Some of the discussion is indeed suggestive (e.g., mental imagery), but some is TOO TANGENTIAL. For example, the HEMI-NEGLECT ARGUMENTS ARE WEAK, they hardly helps us understand the nature of this important condition. The DISCUSSION OF THE LITERATURE SHOULD BE BOTH MORE COMPREHENSIVE AND IN-DEPTH.

The author must provide a MORE STRUCTURED COMPARISON OF HIS PROPOSAL WITH OTHER THEORIES OF SPACE/FORM PERCEPTION. It is only against the background of existing proposals that his contribution can be assessed. And here I mean NOT GENERAL LINES OF INVESTIGATION, SUCH AS NEURAL NETWORK MODELS, BUT SPECIFIC *PERCEPTUAL* THEORIES.

[Note: CAPS above indicate sections highlighted by the editor for particular importance to address.]
 

Is it the VOLUME of referenced material which the reviewer finds inadequate, or is the reviewer refering to some specific literature? Would the reviewer care to specify WHICH "important findings" in the psychophysics of form perception he considers to be so relevant to the Gestalt Bubble Model? Or does he merely suspect that there MAY be some such findings and that the author should seek them out? But the real issue here involves the general nature of the proposal. The reviewer is unhappy that this paper is not a detailed and specific model that makes testable predictions which can be matched against experimental data. And this reviewer will not consider the present paper suitable for publication until it is revised accordingly. What he has failed to understand is the paradigmatic nature of what is being proposed. What I propose is not a detailed model of some specific perceptual effect, but a whole new class of model, motivated by the Indirect Realist perspective that perception involves the construction of a volumetric spatial replica of the external environment in an internal representation. What makes this a paradigmatic idea is the fact that *IF* it should turn out to be right, then it would necessarily have implications on our interpretation of a *large volume* of psychophysical data. In fact, should this idea be proven right, virtually *no aspect* of psychology will be entirely unaffected by this new perspective on the problem. So the volume of psychophysical data which are *relevant* to the model would include much of the literature in psychology. Unfortunately that data cannot be definitive in determining the paradigmatic choice itself, because in paradigmatic debates, both sides often cite the same evidence to support their opposite conclusions. That is because each side interprets the data from the perspective of their own paradigm. For example the most convincing evidence for a spatial representation in the brain is the fact that consciousness exhibits a spatial structure. The structural nature of experience is an indisputable and undisputed fact. But that evidence is convincing only to the Indirect Realist. The Direct Realist interprets that self-same factual evidence as a property of the world rather than of the brain. The two paradigms draw opposite conclusions from the self-same evidence. And they also draw opposite conclusions from the evidence of mental imagery, neglect syndrome, visual illusions, Gestalt phenomena, and virtually every other domain of psychology.

The reviewer suggests a "more structured comparison" with other theories of space / form perception. "Not general lines of investigation such as neural network models, but specific perceptual theories". Here the reviewer clearly reveals his misunderstanding of the scope of the present proposal. For the competing hypotheses which the present model proposes to challenge are *NOT* specific perceptual theories, but *EXACTLY* more general lines of investigation, such as neural network models. Models can be validly defined at many levels, from general concepts to specific mechanisms. Consider for example Marr's and Biederman's models of vision by abstraction of features; Selfridge's Pandemonium model; Triesman & Gelade's spotlight theory of attention; Collins & Quinlan's Spreading Activation model, McClelland & Rummelhart's PDP approach, to name just a few. Some of these models are far more general and conceptual than mine, but are valid models nonetheless. And then of course there is the example of Gestalt theory itself, a concept so general that it can hardly even be called a model. And yet despite its vagueness as to specific mechanism, the Gestalt view of perception serves as an invaluable reminder to resist the temptation to consider only simpler aspects of perception that *can* be described by specific models. It would have been a great loss if the Gestalt ideas had been denied publication because the concept was not sufficiently specified! General models are appropriate in a new field where much remains to be discovered, while more specific models are derived as more exact specification of general models, as a science matures. It is unfortunate that there are so many in the scientific community who consider general discussion of paradigmatic issues to be beyond the bounds of science, which they would reduce to a pedantic pursuit of minute details in hermetically insulated narrow specialty domains. That is a very impoverished view of the enterprise of science!

The set of PREDICTIONS PRESENTED SHOULD CONCERN PERCEPTUAL FACTS. After all this is a perceptual theory, not a theory of consciousness. For example, the last two predictions concern the nature of subjective experience, and are hardly predictions of the model.
 

Is it not the prerogative of the AUTHOR to determine whether his paper is a theory of consciousness or a perceptual theory? What this reviewer fails to see is that every theory of perception is also a theory of consciousness, because the two are inseparable.

The "last two predictions" to which the reviewer objects are the fact that an illusory figure is experienced as a solid spatial surface at high resolution, and that the reversal of a multistable percept is vividly experienced as an inversion of a perceptual data structure. What he means is that I have not specified the computational algorithm of the model sufficient to perform computer simulations that reproduce those phenomena in detail. He is right, I have not. But the vast majority of models out there do not even consider it *necessary* for a model of the phenomenon to produce a volumetric spatial output. The novel and significant message of the present paper is to point out that an adequate model of the phenomenon *MUST* produce exactly such an output. This is the nature of paradigmatic hypotheses, they outline a general approach to a problem, not its detailed solution. It is only after the paradigm has been established that others will feel the need to construct those specific models and perform those simulations. If this reviewer had his way, the paradigm would never even be published as a theoretical possibility for other researchers to consider, so those models would never be built and the predictions never tested.

In summary, the paper has novel, interesting elements that have great potential to become a BBS paper. Nevertheless, the author needs to REORGANIZE THE PAPER SO AS TO HIGHLIGHT THE ACTUAL CONTRIBUTIONS IN A MORE STRUCTURED MANNER.
 

This is the kind of review that I hate most of all! In the first place the reviewer does not bother to summarize the paper, so we have no idea whether he read it or understood it to any depth, or more importantly, whether he understood the principal arguments as intended by the author.

Secondly his criticisms are so vague as to be essentially meaningless. He complains that the philosophical discussion is "not very persuasive", but he does not explain of what he is not persuaded, and why. He demands discussion of "important findings in the psychophysics of form perception" but does not specify what those findings might be. He says that the discussion of the literature should be "more comprehensive and in- depth", but he does not specify what issues should be discussed. He demands "more structured comparison" with other theories, but he does not specify which theories he considers relevant to this comparison. This kind of criticism is such a carte-blanche, there is no way that these vague requirements could ever be shown to have been met.

This reviewer appears to offer a qualified endorsement of the paper, i.e. *revise & resubmit*. But make no mistake about it, this is actually an outright rejection. Because the reviewer has made it clear that the kind of revision that he requires is the kind of revision which would transform the paper from a paradigmatic hypothesis to a simple perceptual theory. And as a perceptual theory it would be promptly rejected for publication because the volumetric filling-in operations would seem unnecessary and neurophysiologically implausible in the absence of the discussion of the paradigmatic issues. If this paper were revised to meet with this reviewer's satisfaction, I would no longer wish to be its author.
 

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Referee #4 Richard Held
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Note: This document is also avaliable on-line at http://cns-alumni.bu.edu/pub/slehar/webstuff/bubw/rebut2-0.html where hyper-links to additional source material are provided.

Lehar turns this approach on its head and takes the bound product as primitive. Lehar's view is iconoclastic and provocative but, in my estimation, as legitimate as that of the "establishment". It is well worth publishing in a journal dedicated to discussion of varied points of view.
 

Here is a man with the vision to recognize a paradigmatic issue when he sees one. This is also a man who apparently shares my belief that a novel idea, clearly stated, and supported by reasonable arguments deserves to be released to the larger community without unnecessary fuss and delay, even if it topples a number of sacred cows in the process!