Individual Responses

Response to Booth

Booth complains that I commit the epistemological fallacy of trying to build public knowledge on the basis of private impressions. Booth objects that phenomenological observations are private, and so "they cannot be wrong-but then neither can they be right." But then he objects that my observations on phenomenal perspective are not only wrong, but that they show "phenomenological slapdash, if not downright dishonesty" (my emphasis). If phenomenological observation cannot be wrong, then how can Booth claim that my observations of phenomenal perspective are wrong? Booth continues "You know and I know that [Lehar] has never looked one way down a road at the very same moment as looking the other way. So it is rank self-deception to write ... that 'the two sides of the road must in some sense be perceived as being bowed' as in the diagram." (my emphasis) In the first place it is not necessary to be looking in opposite directions at the same time to see the curvature of the phenomenal world, all one needs to do is to look in one direction and observe that the parallel sides of a road meet at a point at a distance which is less than infinite, and that those parallel sides appear straight and parallel throughout their length. And in the opposite direction one sees exactly the same thing, and in between one sees a spatial continuum exactly as depicted in figure 2. If anyone is guilty of "rank self-deception" it is Booth, if he denies the plain evidence of his own visual experience. Phenomenological observation can indeed be right and it can be wrong, and Booth's phenomenology is just plain wrong if he can't see perspective foreshortening in the world around him!

Return to Commentaries

Return to Booth Commentary

On to Next Commentary

Response to Dresp

The commentary by Dresp concludes "The Gestalt Bubble model, as a scientific approach to consciousness, can be filed DOA (Dead On Arrival)." But again we have a clear case of inability to grasp the paradigmatic message of the target article, so Dresp's objections to it cannot fail to miss the mark.

Dresp complains that I fail to make clear the link between the Gestalt Bubble model and general theories of consciousness. "What the model has to do with consciousness ... remains totally unclear. Neither the fact that we are able to consciously experience and describe 3-D shapes as entities and wholes, nor the fact that we can find laws or codes describing how these emerge perceptually, implies or proves that consciousness is necessary to see and move around in 3- D space." The link to general theories of consciousness is through the philosophy of identity theory, (Russell 1927, Feigl 1958) as explained in the target article, whereby mind and brain are not separate and distinct, but are ontologically one and the same thing. The presence of spatial structures in the perceptual representation is identically equal to a conscious experience of those structures.

Dresp simply assumes as if it were plain fact that the experiential component of consciousness is separate and distinct from the physical mechanism by which it is instantiated, and therefore a model of the mechanism cannot be a model of the experience, because the experience cannot be modeled in principle. But it is at least equally likely prima facie that experience is not separate and distinct from the mechanism that carries it, but that experience is a physical process taking place in the physical brain, so a model of the mechanism would automatically also be a model of the experience. In fact, this is by far the more parsimonious explanation because it employs a single explanans, the brain, to account for the properties of mind and brain. Identity theory is an equally valid paradigmatic alternative, which cannot be dismissed without demonstrating why it is less credible than a mystical non-physical theory of experience beyond science. Furthermore, the Gestalt Bubble model is explicitly defined as a model of experience, rather than its neurophysiological correlate. How Dresp fails to see the connection between a model of experience and the experience it models is beyond me.

Dresp objects to my exhortation to discover the real truth behind visual processing. "Who said that science has to bother with metaphors such as 'truth' ? " she asks. I cannot begin to fathom what she means by this comment. Science is all about modeling objective external reality, a truth that science presupposes to exist. Either there are "pictures in the head" as explicit spatial structures, or there are not. And whether or not there are pictures in the brain is of primary importance for psychology, philosophy, and neuroscience. Simply defining those pictures as a mystical non-physical entity brings us no closer to understanding how consciousness arises in brains. The Gestalt Bubble model may be "Dead On Arrival" in Dresp's mind, but that is only because her mind is closed to the arrival of alternative paradigmatic formulations.

"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."

Return to Commentaries

Return to Dresp Commentary

On to Next Commentary

Response to Duch

Duch is another commentator incapable of thinking outside his paradigmatic box. Duch asks: "How can the physical skull encompass non-physical, inner world? The 'world inside the head' is a metaphor, and it does not make much sense to invert it, unless one believes that there is some kind of physical world squeezed inside the skull." That is precisely the hypothesis which is presented, although it is a perceptual world, not a physical one which is squeezed inside the skull. This notion seems to Duch so absurd from the outset that he cannot believe that is what I am proposing. Duch states, as if plain fact, that "interpretation of the spatial structure of the states of visual system has nothing to do with their physical location." This is exactly the issue brought into contention by the target article. If he is to contest this assumption, he must explain which incredible alternative he wishes to defend in its place. Does he claim that consciousness does not exist at all, as Dennett would have us believe? Or does he allow that it exists, but in some hidden dimension inaccessible to scientific scrutiny as Velmans proposes? If so, how does he address my critique that his view of consciousness is a religious rather than a scientific hypothesis? Duch also complains that I misrepresent the Neuron Doctrine by omitting discussion of dynamic recurrent neural networks. He must have missed my discussion of the dynamic recurrent neural network models of Grossberg, and their fundamental difficulties with modeling spatial experience (Section 3 of the target article).

Return to Commentaries

Return to Duch Commentary

On to Next Commentary

Response to Fox

Fox begins his commentary with the complaint that "[Lehar] ignores much of what is known in perceptual and brain science." The truth is that Lehar challenges much of what is "known" in perceptual science. Far from ignoring, I have taken pains to point out the errors of what is known in perceptual and brain science. If Fox begins from the outset with the assumption that those supposed "facts" are indisputable, then he is wasting his time reading a hypothesis that they may perhaps be mistaken.

There is much in Fox's commentary which is deeply mysterious. Fox accuses me of maintaining the "Cartesian mind-body distinction." How he could have come to this erroneous conclusion is beyond me. The central hypothesis of the target article is an identity theory, whereby mind is nothing other than the functioning of the physical brain. This monistic view is about as diametrically opposed to Cartesian dualism as it can possibly be. Furthermore, in Section 2.3 I explicitly refute Cartesian dualism as a spiritual rather than a scientific hypothesis.

Return to Commentaries

Return to Fox Commentary

On to Next Commentary

Response to Grossberg

In the target article I commended Grossberg for advocating explicit filling-in to account for Gestalt illusions, but chided him for not extending that same reasoning into the third dimension. To this Grossberg responds that I have not kept up with the modeling literature, he cites the FAÇADE and LAMINART as models that explain many 3D figure-ground, grouping, and filling-in percepts, including transparency, and use an explicit surface filling-in process. This I do not doubt. But in both FAÇADE and LAMINART, depth is handled in a disparity fashion, with left and right eye image pairs and disparity images to represent depth information. In neither of those models is there a three-dimensional volumetric spatial matrix with receptive fields at every location and every orientation in three dimensions, as would be required for a neural network model of spatial experience. While FAÇADE and LAMINART do perform explicit filling-in of both contours and surfaces, the filling-in itself does not propagate in the third dimension by diffusion as it does in the other two. The third dimension is handled very differently than the other two, and the result is a 2¹/₂-D sketch rather than a full volumetric spatial matrix. Whatever their merits as a neurophysiologically plausible model, these models leave something to be desired as perceptual models, because perceptual experience is fully volumetric and three-dimensional, and multiple depth values can be experienced in any direction.

If Grossberg's argument that explicit filling-in is required to account for two- dimensional illusions has any validity at all, then it should apply just as well to three-dimensional perception as it does to two, at least for a perceptual model that models the experience rather than its neurophysiological correlate.

Return to Commentaries

Return to Grossberg Commentary

On to Next Commentary

Response to Gunderson

Gunderson observes that visual experience consists of more than just a spatial structure, it is a spatial structure that is experienced as being viewed from a particular point, and that this aspect of viewing from a point is not captured in the Gestalt bubble model. In the first place whether or not this objection is valid, the fact remains that experience is an explicit spatial structure, and the structural aspect of experience is captured in the Gestalt bubble model. That alone is already a significant quantification of that aspect of experience.

But in fact the Gestalt bubble model goes further to suggest that the experience as if viewing from a point is itself an illusion. Once we recognize the world of experience for the internal model that it is, it becomes evident that our objective noumenal "self" is not the body-image homunculus observed at the center of that world, but in fact the whole world of experience is part of our real self. The blue of the sky is not observed from the egocentric point, but it is experienced out there where it lies at the surface of our perceptual sphere. The blueness of that azure dome exists at the location where it is experienced, it is in no sense transposed or projected to the egocentric point. There is nothing special at all experienced at the location of egocentric point, which is experienced as an empty void of phenomenal space inside the phenomenal head, just like any other empty space in the phenomenal world.

There are three factors that contribute to the vivid illusion of viewing the world from a particular point. The first is the body-image homunculus which we take to be our real "self" because that particular piece of the phenomenal world is under our direct volitional control. Under large doses of hallucinogenic drugs such as LSD the perceptual distinction between self and non-self tends to disappear, as the body image merges with the background, leaving the entire sphere of perceptual experience to be identified as "self", a common theme also of Buddhist phenomenology. The second contributory factor is the warped geometry of phenomenal space that is organized around a center, the point of highest perceptual resolution. Finally, the illusion is bolstered by the fact that perceived surfaces are only perceived modally when they are exposed to the egocentric point, as if they were indeed being viewed from or by the egocentric point. Objects not exposed to the egocentric point are invisible to direct modal experience, and are therefore experienced in amodal fashion.

Return to Commentaries

Return to Gunderson Commentary

On to Next Commentary

Response to Hochberg

Hochberg suggests an alternative, less wholistic model-a stage set rather than an all-encompassing bubble, with an abrupt discontinuity at a certain depth, where a proximal percept of a full 3-D road with perfectly parallel sides, changes abruptly to a flat two dimensional experience at right angles to the view direction, in which the sides of the road converge to a point in the plane of the backdrop. No matter how hard I try I cannot see the world this way; I always see the two extremes of near and far perception seamlessly connected through a continuous intermediate zone, wherein the sides of the road are perceived in full three- dimensions, and yet they are also perceived to converge, and they are perceived to be parallel even as they converge.

I acknowledge that perception is somewhat more fragmented than the Gestalt Bubble model suggests. For example every visual saccade presents a momentary experience perhaps somewhat like a stage set. But the most salient and immediate aspect of conscious experience is the way these individual theatre sets are welded together into a unified sphere of spatial experience. Whatever direction we gaze, we are constantly aware of where that gaze is directed in the global sphere of surrounding space, and the objects perceived in that direction are perceived to be located in that part of global space. The experience is more that of a stable structured surrounding space, than a series of theatre sets showing successively on the same stage.

Hochberg cites visual illusions that vary as a function of where they are attended, as evidence to disqualify the Gestalt Bubble model because the same Gestalt is in view wherever it is attended. There are two aspects of spatial experience that must be carefully distinguished, we might call them global and focal. In the global experience our view is of a perfectly stable surrounding world, as suggested in figure 2 of the target article, whose entire surface is painted in modal colors, because whichever direction we look, that is the way it appears. The other aspect of experience is focal, the immediate experience that we are looking in a particular direction. The world appears at higher resolution in the direction of gaze, while the rear hemisphere behind our head is blank, as suggested in figure 15. Both global and focal aspects are observed in our experience, so they should both be represented in a model of that experience. The combined experience is modal and focal in the direction of sight, but amodal in the hidden rear portion of the field, as indicated by the dashed lines in figure 15, although successive saccades in different directions create an illusion of the complete modal sphere suggested in figure 2.

The point of the Gestalt Bubble model is not to deny that there are localized focal processes active in perception, but merely to add that there is also a single globally unified perceptual experience, and the localized focal experiences are perceived to be embedded at specific locations in this larger global framework of spatial experience.

Return to Commentaries

Return to Hochberg Commentary

On to Next Commentary

Response to Hoffman

Hoffman argues that the perceived world of the Gestalt Bubble model is not a veridical replica of the external world, but merely a useful "user interfaces" to the external world, with no more need to resemble that world than a Windows interface needs to resemble the diodes, resistors, and software of a computer. That there is possibly no real resemblance at all between the structure of our phenomenal world and the real external world that it represents. Hoffman proposes to replace indirect realism with this species-specific "user-interface" theory of perception. But that is exactly what I have proposed in the Gestalt Bubble model. Nowhere was it stated that the phenomenal world is in any sense identical to the external world. Phenomenal colors are very much more impoverished than the chromaticity of physical light, and phenomenal perspective shrinks the infinite external world into a finite bounded bubble. These are clearly species-specific "user-interface" simplifications of external reality. The "realism" in "indirect realism" is already modulated by the word "indirect", i.e. the phenomenal world is a very real and direct view of processes taking place within our own brain, and those processes in turn represent indirectly the structures and surfaces presumed to be present in the more remote external world.

Return to Commentaries

Return to Hoffman Commentary

On to Next Commentary

Response to Laming

Laming is yet another commentator who fails to grasp the paradigmatic nature of the proposed model, and presents as counter-arguments the axioms of his own paradigmatic alternative. These axioms are presented as if they were plain facts, rather than unsubstantiated initial assumptions. Laming insists that some parts of visual experience can be shared with others, while the remainder are private, and therefore there cannot be a natural science of perception. So a psychophysical report for example that a subject can or cannot see an extended red object, is a valid subjective report. But the redness, and spatial extendedness of that perceived object are not validly reportable because they are private. Curiously, the very aspects of experience which Laming considers illegitimate, including all of the Gestalt properties surveyed in paragraphs 5 and 7 of the target article, are exactly the aspects of experience that reveal the spatial structure that Laming insists have no physical reality. Laming must explain why the spatial aspect of perception is so private that it cannot be reported, when the Gestalt Bubble model clearly demonstrates how the spatial aspects of perception can be reported and quantified in a spatial model. If he contests my phenomenology and claims to not see the sky as a dome and the sides of a road converge to a point, then he should tell us what he sees instead. It is a paradigmatic choice of Laming's to consider the spatial extendedness of perception to be unreportable, not a statement of incontestable fact. And if Laming chooses to believe that phenomenal consciousness is not a physical entity in the brain, he should address the clear objections to that paradigm outlined in the target article. In particular, conscious experience, according to Laming, is a spatial structure, it is a structure that exists, and yet it does not exist in any space known to science, and it is in principle undetectable by scientific means. This is a religious or spiritual hypothesis because it is impossible in principle to disprove. To accept Laming's view of consciousness is to declare consciousness in principle forever beyond explanation in scientific terms, which would then become a self-fulfilling prophecy.

Return to Commentaries

Return to Laming Commentary

On to Next Commentary

Response to Lloyd

Lloyd presents a very clever argument by analogy that appears to punch a hole through the central premise of isomorphism. Consider the statement from the target article.

"The fact that the world around us appears as a volumetric spatial structure is direct and concrete evidence for a spatial representation in the brain."

Lloyd suggests that the absurdity of this statement can be revealed by substituting "colored" for "spatial" in this passage. Phenomenal color experience defines a three-dimensional relational structure of phenomenal color space. But, Lloyd correctly objects, the fact that we experience phenomenal color does not mean that the color solid appears anywhere in our brain, and by the same token, spatial experience does not imply a spatial structure in the brain.

This objection is already addressed in the target article by the specification of information content as the one quantity which is necessarily preserved across the mind/brain barrier. A color experience is indeed a three-dimensional relational structure, not so different in principle from the color phosphor dots on a television monitor. It takes three values of three phosphor dots to encode a single point of color on your screen, and those three values define a single point in Red-Green- Blue [RGB] space. However a single point on a television screen does not define an entire color solid, but merely one point in that three-dimensional color space representing the color currently represented at that point. The color solid is not explicitly present anywhere, but the relational structure that it encodes is implicitly present in the range of possible values of the three phosphor dots.

Spatial perception is different from color perception in this one significant aspect, that every point in perceived space can be perceived with a distinct color. That means that there are as many separate and potentially distinct color values in a perceived surface as there are resolvable points across every surface of that scene. The points in a perceived surface are perceived simultaneously and in parallel, and together they define a relational structure in which every point bears a specific spatial relation to every other point in that perceived surface. This is quite different from the implicit structure of color space that encodes only one color at a time, because spatial perception encodes a whole spatial array of color values, all of which are simultaneously present in experience.

Return to Commentaries

Return to Lloyd Commentary

On to Next Commentary

Response to Luccio

Luccio takes issue with my characterization of Gestalt theory as a representationalist theory; he claims that it is neither representationalist, nor antirepresentationalist, it is merely indifferentist to the epistemological question. There have been different schools of Gestalt, not all of which have shared the same philosophy. But at least Koffka and Köhler, and therefore by implication presumably Wertheimer also were definitely representationalists. Koffka makes the most clear representationalist case with his distinction between the "geographical environment" (the objective external world) and the "behavioral environment (the phenomenal world), and he clearly stated that the behavioral environment is located inside the geographical body in the geographical environment (see Koffka 1935, p. 40, Fig. 2). Köhler expressed his representationalist views most clear in Köhler (1971, p. 125).

Return to Commentaries

Return to Luccio Commentary

On to Next Commentary

Response to MacKay

Return to Commentaries

Return to MacKay Commentary

On to Next Commentary

Response to Markovic

Markovic is puzzled how I can claim at one point that "the internal perceptual representation encodes properties of distal objects rather than of a proximal stimulus", while at another I state "the direct realist view is incredible because it suggests that we can have the experience of objects out in the world directly, beyond the sensory surface, as if bypassing the chain of sensory processing". Why, asks Markovic, would the thesis that distal objects are mapping onto the phenomenological domain without neural intervention be incredible and mysterious, while the idea about the projection of internal representation onto the external perceptual world not be incredible and mysterious? How is it possible that perception is partially indirect (representational), and partially direct (distally oriented)?

Perception is entirely indirect; what we experience is in every sense inside our physical head. The 'distal orientation' of perception is seen in the form, or dimensions in which perceptual information is expressed. The perceived world is expressed not in terms of the proximal image on the sensory surface, i.e. a two- dimensional pattern of brightnesses, but in terms of actual three-dimensional objects and surfaces in a world that we take to be reality. We do not see visual patterns and infer them to be a table, we experience a table, expressed in terms of volumes of perceived wood embedded in a volume of perceived space. But that world information does not enter experience directly in some magical mystical manner, but indirectly by the conventional route of sensory input, and that input is expanded out or reified in the brain to become the spatial percept that we experience.

Return to Commentaries

Return to Markovic Commentary

On to Next Commentary

Response to McLoughlin

McLoughlin's commentary is interesting as I believe he represents eloquently the consensus view in neuroscience today. McLoughlin points out that a volumetric space can be expressed in a sparse, more symbolic code without recourse to an explicit spatial array, with objects represented as tokens, with x, y, and z, location, and so forth. There are many aspects of mental function, such as verbal and logical thought, that are clearly experienced in this abstract manner. But visual consciousness has an information content, and that content is equal to the information of a volumetric scene in an explicit volumetric representation. Every point in the volume of perceived space is experienced simultaneously and in parallel. To propose that the representation underlying that experience is a sparse symbolic code is to say that the information content of our phenomenal experience is greater than that explicitly expressed in the neurophysiological mechanism of our brains.

McLoughlin endorses O'Regan's (1992) concept of seeing as an active process of probing the environment as though it were a continuously available external memory. But probing the world with visual saccades, especially in the monocular case, is nothing like accessing a memory, internal or external, because every saccade presents only a two-dimensional pattern of light. The three-dimensional spatial information of the external world is by no means immediately available from glimpses of the world, but requires the most sophisticated and as-yet undiscovered algorithm to decipher that spatial information from the retinal input. Furthermore, in the absence of a global framework to register the information from each saccade in its proper place, vision as described by O'Regan would be indistinguishable from apperceptive agnosia, a visual integration failure. In other words the condition of apperceptive agnosia is the absence of a visual function whose existence O'Regan effectively denies. McLoughlin is right that the brain need not explicitly represent more than it needs at any particular time, and can make do with a sparse or abbreviated representation of the world. But he misses the paradigmatic point that the world we observe in experience is already that sparse representation, the real world beyond experience being infinitely more complex than our experience of it. So the brain must explicitly encode exactly as much detail as we observe in experience, no less, and unbiased phenomenological observation clearly reveals a spatially structured world.

McLoughlin casts doubt on the reliability of phenomenological observation by pointing out that naive observers are surprised to discover that they have a fovea and amazed that they have a blind spot in each eye. True enough, but those same naïve observers can be easily educated by the most convincing demonstration of all, phenomenological observation of their own loss of resolution in peripheral vision and of their own blind spot. Like any tool, phenomenology is useful only if employed with intelligence.

McLoughlin argues that the fragmented architecture of the visual cortex into separate retinotopic maps requires a fragmented model of vision. But that is true only for a purely neurophysiological model that cares nothing about phenomenology, where the unity of visual experience is its most salient feature. But a neuroscience that explains everything about the brain except for how it generates consciousness, is a neuroscience that explains nothing, because it is consciousness that makes the brain interesting in the first place. To declare from the outset that the unity of consciousness requires no explanation is to guarantee that no explanation will ever be found.

Return to Commentaries

Return to McLoughlin Commentary

On to Next Commentary

Response to Randrup

Randrup complains that my position is not really materialist, because I say in the target article that "there remains a subjective quality (or quale), to the experience of red for example, which is not in any way identical to any physical variable in the brain." (section 4) This quoted passage however represents not my own view, but my summary characterization of Chalmers' "hard problem" of consciousness, and why it is considered by some to imply a fundamental dualism. According to identity theory the difference between subjective experience and its objective physical realization is a difference in viewpoint or perspective, rather than an ontological dualism, and that makes the Gestalt Bubble a materialist position.

Return to Commentaries

Return to Randrup Commentary

On to Next Commentary

Response to Revonsuo

Revonsuo strikes at the core of another paradigmatic issue, panexperientialism. Revonsuo cites phenomena such as neglect and blindsight that suggest that perceptual information can be processed without necessarily entering consciousness. But as in the case of most paradigm debates, both camps can usually muster an explanation for most any phenomenon raised, although each explanation is consistent only within its own paradigm, and sounds patently absurd from within the other.

For example blindsight, the apparently unconscious processing of visual information, can be explained as a case of amodal perception. When the blindsight patient reports a vague suspicion of motion in the absence of an experience of a moving object, he is reporting a conscious experience of a vague suspicion of motion without actually seeing anything in motion. Even people with normal vision commonly have such experiences in the periphery, and many psychophysical experiments measure very vague perceptual experiences at the threshold of detection which are not so much "seen" as suspected to have possibly appeared. Many philosophers deny that amodal percepts, or other forms of non-sensory knowledge, can be validly considered as conscious processes, insisting instead that only modal experience is experience. But if we exclude the amodal component of perception from conscious experience, then by definition amodal perception is blindsight. It seems more parsimonious to suppose that amodal perception is consciously experienced, even if only amodally, than to suppose that something experienced can be unconscious.

Other examples of apparently unconscious processing can be explained in the panexperiential view as separate parallel and largely independent conscious processes in the brain. The part of the brain that performs the processing is indeed conscious of its own performance, but it is not in touch with the part of the brain that reports on that processing, so no processing is reported. Similarly, unconscious processing in dichotic listening can be explained by separate parallel streams of consciousness, one of which overwrites the other in memory, which is thus never recalled. This is not to say that the evidence of neglect and blindsight favors panexperientialism, but merely that it does not refute it. The motivation for panexperientialism lies elsewhere.

It is true, as Revonsuo suggests that the proto-consciousness hypothesis can probably not make testable predictions, but that is not why it was invoked in the target article. It was raised to plug up some otherwise serious holes in a purely monistic or physicalist explanation of conscious experience. This paradigmatic choice avoids a most subtle residual dualism hidden in Revonsuo's alternative.

As long as a sharp step or abrupt discontinuity is allowed between conscious and unconscious processes, there will always be an explanatory gap, because physically, the brain can be disassembled into ever smaller pieces all the way to atoms and molecules, whereas in Revonsuo's view consciousness does not have this ability to be disassembled, but disappears abruptly as soon as the minimal conditions for it are no longer met. To be clear, I do not dispute that consciousness may exhibit, and indeed appears to exhibit an abrupt cut-off for example when falling asleep or waking up, although intermediate semi-conscious states are also known. If consciousness appears abruptly at some level of organization, then something else physically observable must come into existence at that point also.

For example consciousness might be identified with a holistic process such as spatial standing waves of electrochemical resonance in the brain. (Lehar 2003) Resonance shares with consciousness the property of coming abruptly into being when the conditions for their formation are just right, as when blowing a note in a musical instrument. And yet standing waves are not some supervenient spiritual entity, but a real physically measurable phenomenon that emerges holistically in a physical system. But if standing waves were the physical substrate of consciousness, then that would suggest that musical instruments also necessarily posses some form of primal spatial consciousness. And when global consciousness breaks down in the brain, whether due to sleep or anesthesia, the global synchrony does not disappear, so much as it breaks up into a million fragments of locally isolated coherence. Would these fragments not each experience an isolated fragmentary consciousness? If not, then we have again an abrupt discontinuity that suggests a dualism between experience and its physical correlate. Alternatively, parallel fragmented states of consciousness are indeed experienced during periods of "unconsciousness" but they never register in memory and are thus quickly forgotten, as are many dreams.

A further problem with the abrupt discontinuity of consciousness is that it opens the problem of the "bridge locus" in the brain, i.e. the question of why some very special parts of the brain become conscious while other parts do not. It also leads to problems with partial or fragmented consciousness, as in the split-brain patients, and in cases of multiple personality syndrome, and hypnotic or trance states, which all seem to indicate multiple parallel or alternating consciousnesses in a single brain. Whether the disassembled pieces of consciousness can be usefully considered to be conscious in any real sense is admittedly a semantic question. But what is not semantic is the question of whether consciousness can be disassembled into component pieces, as can the matter and energy in the brain, or whether the mind operates by different laws than the matter that is sometimes its physical correlate. The only self-consistent physicalist explanation is that complex consciousness in a complex brain occurs by the same principle as simple consciousness in simpler brains, and that same argument propagates all the way down to the root of the phylogenic tree and beyond. Consciousness is what it feels like for matter to exist, and complex human consciousness is what it feels like to be the waves of energy resonating in a human brain.

Return to Commentaries

Return to Revonsuo Commentary

On to Next Commentary

Response to Rosenthal & Visetti

Rosenthal & Visetti are generally supportive of the perceptual modeling approach proposed in the target article. However they are puzzled as to whether the proposed mechanism of emergence in the model is motivated primarily by the emergent properties of perception, or whether it is a physicalist model, whose spatial matrix and field-like interactions represent physical space and physical forces in the brain.

Return to Commentaries

Return to Rosenthal Commentary

On to Next Commentary

Response to Ross

Ross agrees that a simple neuron doctrine cannot account adequately for size constancy in perception, but contends that more complex neurological models show promise. He then cites a number of neurophysiological models that account for some aspect or other of size constancy. But curiously, none of the models that Ross cites account for the one aspect of size constancy which is the central focus of the target article, that is the fact that objects in space appear as solid volumetric objects embedded in a volumetric surrounding space, and that space has the peculiar property that it's size scale shrinks progressively in nonlinear fashion with distance from the egocentric point.

Return to Commentaries

Return to Ross Commentary

On to Next Commentary

Response to Schirillo

Return to Commentaries

Return to Schirillo Commentary

On to Next Commentary

Response to Tse

Tse is generally supportive of the Gestalt Bubble model, and offers a more general analysis of the why the visual system operates as it does. Tse identified two general principles by which the visual system attempts to correct errors. One involves completing missing information on the basis of knowledge about what most likely exists in the scene, i.e. perceptual "filling-in," and the other involves exploiting the physical stability of the environment as a reference frame with respect to which the eyes and body can move. An interesting aspect of this view is that the visual system implicitly understands its own limitations, and attempts perceptual filling-in only when it "knows" that it has failed to detect something that it believes must be present.

Return to Commentaries

Return to Tse Commentary

On to Next Commentary

Response to Velmans

Max Velmans' commentary was intriguing because Velmans' Gibsonian view and the Gestalt view, share so much in common as to be almost identical, and yet they find themselves on opposite sides of the epistemological divide. Velmans' holographic analogy is very apt. There is indeed no "picture" as such on a holographic plate, just a fine-grained pattern of interference lines. But in order for the picture to be experienced by a viewer, or to be available for data access in an artificial brain, that picture must first be reified out of that pattern of interference lines into an actual image again, i.e. the holograph must be illuminated by a beam of coherent light. After passing through the holographic plate, that beam of light generates a volumetric array of patterned light, every point of which is determined by the sum of all of the light rays passing through that point, and it is that volumetric pattern of light in space that is observed when viewing a hologram.

So if holography is to serve as a metaphor for consciousness, the key question is whether the metaphorical hologram is illuminated by coherent light to produce a volumetric spatial pattern of light, or whether the hologram in experience is like a holographic plate in the dark. If it is the former, then conscious experience in this metaphor is the pattern of light waves interfering in three-dimensional space. It is a spatial image that occupies a very specific portion of physical space, and it requires energy to maintain it in that space. This is exactly the kind of mechanism we should be looking for in the brain. If it were the latter, as Velmans suggests, then why would the shape of our experience not be that of the interference patterns etched on the holographic plate, rather than the volumetric image that they encode? What magical substance or process in conscious experience performs the volumetric reconstruction that in the real universe requires an actual light beam and some complicated interference process to reconstruct? If it is a spatial structure that we observe in consciousness, then it is a spatial structure that we must seek out in the brain, not a potentially spatial structure that remains stillborn in a non-spatial form. Otherwise the spatial image-like nature that is so salient a property of subjective experience must remain a magical mystical entity forever in principle beyond the reach of science.

Velmans' concluding paragraph reveals the real reason why he rejects representationalism. "Stick your hands on your head. Is that the real physical skull that you feel or is that just a phenomenal skull inside your brain? ... If we live in an inside-out world as Lehar suggests, the skull that we feel outside our brain is actually inside our brain, and the real skull is outside the farthest reaches of the phenomenal world, beyond the dome of the sky. ... Our real skulls are bigger than the experienced universe. Lehar admits that this possibility is "incredible." I think it is absurd." And with this I believe Velmans touches on the principal reason why this alternative has been given so little consideration.

Return to Commentaries

Return to Velmans Commentary

On to Next Commentary

Response to Wright

Wright supports the representational stance in the target article, and provides further arguments to defeat the alternative direct realist view. Wright objects however to the use of the term "subjective" when applied to the sensory field, because the sensory representation of colored volumes embedded in perceived space is thoroughly nonconceptual, and therefore no kind of subjective judgement is involved at that low level of experience. If television is an apt analogy for the televisual function of vision, Wright suggests I acknowledge the nonconceptual nature of the pattern of glowing phosphor dots on the television screen.

Return to Commentaries

Return to Wright Commentary