Joint referees #2 Jonathan Opie & Gerard O'Brien
Lehar's article is welcome, and raises issues which cognitive science has lately neglected or ignored. His approach is, to our knowledge, quite novel. Let us say at the outset, therefore, that we believe this material warrants BBS treatment. It is likely to generate a significant amount of critical reaction and commentary across a broad range of disciplines. At the same time, there are some weaknesses in the article which we would like to see addressed before its eventual publication. Some of these are relatively minor, others concern the clarity and coherence of the argument.
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 it better to use "... the primacy of 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 characterising 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.
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.)
4. section 2.4, par.1
Lehar says that psychology is the "science of the...subjective side of the mind/brain barrier". We agree that conscious experience is a significant (and neglected) explanandum of psychology. However, intelligent behaviour is also an explanadum of psychology. It would be better to say: "psychology is not only the science of human behaviour, but also the science of the psyche...". 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"?
5. section 2.4, par.2
a page reference for the searle 1992 is needed.
6. section 2.4, par.3
It 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).
7. section 3
Lehar appears to accept chalmers' pessimistic analysis of the "hard" problem of consciousness. This is surely premature when there is a large literature that has responded to chalmers' diagnosis of the situation. Some reference to this literature would be helpful. (note, the singular of qualia is "quale".)
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.
9. section 4
In this section Lehar initially claims that his perceptual modelling 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".)
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, how ever 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. Similarly, the stability of the perceptual representation is *a result of* the intrinsic constraints, it doesn't "encode" those constraints. At best it displays them. Incidentally, talk of "the most stable configuration" or the configuration with "the greatest simplicity, or pragnanz" (next par.) doesn't actually explain much. A principle like pragnanz is kind of a higher-order gestalt principle that itself stands in need of some explanation in terms of a computational mechanism. Lehar, as he admits, offers no such mechanism.
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.
12. section 8.6
the move here, if we understand it, explains subject reports under "objective instruction" conditions (sect.6.3). We wonder if it would be appropriate to make explicit mention of how the model handles subject reports under "projective instruction" conditions.
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.
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 represenation" 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. 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.s. implicit representation" (section 4, par.2).
If, at the end of the day, Lehar does ascribe 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: Items in bold font indicate sections highlighted by the editor as particularly important to address.)
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.
16. section 8.6
(Note: Items in bold font indicate sections highlighted by the editor as particularly important to address.)
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?
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 relaxation 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
To conclude, let us reiterate that we think this is an insightful and valuable paper. We look forward to seeing it in print.