There is no place in the brain where it all comes together?

The title is a familiar mantra I hear from philosophers, a mantra that was largely accepted upon publication of Consciousness Explained. It is advanced as both an anatomical fact and a functional fact. What evidence is cited from neuroanatomy in support of the anatomical claim? I couldn’t find anything in Dennett’s book.

Before writing up something more detailed, I’ll just sketch where I plan on going. Most importantly the mantra needs to be clarified. What evidence would convince someone that a certain region of the brain was indeed “where it all comes together”?  What is the scope of the ‘all’ in ‘it all comes together’? I suppose it means ‘There is no nucleus or cortical area that receives inputs from all sensory modalities’ or something like that. But there are plenty of candidates for such sensory convergence: basal ganglia, certain thalamic nuclei especially the reticular nucleus, the reticular formation in the brain stem, and perhaps some areas in the frontal cortex (e.g., some of the premotor areas). Note, I’m not saying any of these regions are the locus of consciousness, though some are probably important.

Ultimately what is important for Dennett is the functional claim rather than the anatomical claim (in personal correspondence, he agreed with this). That is, the claim that there is no Cartesian Theatre is orthogonal to the anatomical claim that there is no place (in the brain) where it all comes together.

So, that’s the direction I’m going. I was just wondering if, perhaps, I had missed some evidence the philosophers were using for the anatomical interpretation of the mantra. Since the functional arguments never really convinced me, and there doesn’t seem to be evidence for the anatomical side of the claim, I am not convinced there is no Cartesian Theatre. As Dennett says “It sure seems as if there is a Cartesian Theater” (italics mine).

32 Comments

  1. gualtiero

    Interesting questions.

    I think Dennett would be happy to grant that there are brain areas that receive inputs from all sensory modalities. Still, he would reject the conclusion that such areas are the locus of consciousness. His reasons are not anatomical or even physiological. As I’m sure you know, he thinks there is something incoherent about the very idea that there is a unique and determinate neural event behind our feelings and reports about our conscious experience. He gives various thought experiments to that effect.

    Dennett’s conclusion is actually independent of whether the putative unique neural realizer of consciousness is localized in a specific area or distributed over many areas. Dennett usually attacks the view that the putative unique and determinate neural realizers of conscious experiences are localized in a specific place (the “Cartesian theater”), but he is equally unhappy with the idea of a neural realizer of consciousness distributed over many areas.

    The problem I have with his view is that (1) as you point out, his view is not based on any neuroscientific evidence and (2) the arguments (“intuition pumps”) he gives, in my opinion, are insufficient to establish his conclusion.

  2. Eric Thomson

    Yes, I was just focusing on the anatomical claims. The psychological and anatomical dimensions of that slogan are often conflated (even by Dennett, hell even using the spatial locution invites this conflation), and many people I’ve met think the slogan applies to anatomy. The average neuroscientist, on the other hand, would be like “Huh? What the hell does that even mean?”

    The orthogonal psychological argument about Cartesian Theatres is interesting. I remember being quite unimpressed with his arguments that there is no fact of the matter to distinguish Orwellian and Stalinesque memories.

  3. The notion of a theater of consciousness has been around for a very long time. But until recently, no one has offered a biologically plausible theoretical model of brain mechanisms and systems that are competent to constitute an internal virtual world — the singular neuronal space/stage within which all objects, actors, and features can be bound and experienced in a globally coherent fashion. Perhaps this is why the idea of a *Cartesian Theater* has not been taken as seriously as it should be. In my paper “Space, self, and the theater of consciousness”, A.Trehub / *Consciousness and Cognition* (2007) 310-330, I summarize the neuronal design of a putative brain system (the *retinoid system*) which can realize a phenomenal “stage”. In this paper, I also show how the operational properties of the retinoid system can explain the occurrence of striking perceptual phenomena that have puzzled investigators for many years.

  4. Eric Thomson

    Hi Arnold: thanks for the response.

    Dennett’s favorite example in CE is the ‘phi phenomenon’ (red dot appears, then a little later at a slightly different location, a green dot). It appears that there is a dot moving, changing from red to green. Dennett uses this to argue that there is no way to empirically determine whether the subject:
    a) Sees a red dot, then a green dot, and then retroactively forms a memory (incorrectly) of a red dot turning into a green dot, which they then report.
    b) Sees a red dot turning into a green dot (a ‘hallucination’), and correctly reports this.

    While I don’t like this example, or any of his examples, as it isn’t ‘objective’ psychophysics (there is no way to get a measure of correct performance in the task like they do with more traditional psychophysics: e.g., color matching experiments).

    However, passing over that objection to all his examples (the same applies to the ‘rabbit’ phenomeonon), have you looked at how your retinoid model deals with the phi phenomenon?

  5. What if the locus of consciousness is not an anatomical (physical) place but a “code”? Coalitions of neurons firing in synchrony strengthen the connections among frontal and parietal cortex?
    What if the “homunculus” is really conscious and is located in areas that instantiate executive functions (working memory)?

  6. Eric Thomson

    Good questions. My first version discussed this a little, but it started to grow too long so I just focused on the “straw man”, the anatomical claim that there is an area or nucleus where things come together. It turns out not to be a straw man, but it is not clear at all what relation such zones of convergence (with apologies to Damasio) have to consciousness, if any.  My aim was more simple, to just show that taken as a literally spatial, anatomical claim, it is questionable.

    I don’t have a well-developed positive story about consciousness, but the not-well-developed story I tell myself is probably a version of Cartesian Materialism (I think the contents of consciousness are, roughly, a ‘perspectival world model’, that models the events in the world and body that are happening now and which are causing sensory receptors to fire). For instance, you don’t see the back of a computer you are looking at, even though you can think about it. You only see the parts that are causing your photoreceptors to respond. And by ‘now’, that is a little tricky. I tend to think events in consciousness are represented as happening now, even though those events are actually models built up over time.

    This is related to Richard Gregory’s theory, in which qualia serve as a ‘tag for the present.’ There are all these representations running around our brains, most of them memories of what happened a week or hour ago. Qualia are special in that they tell our decision making mechanisms what is happening now, help to segregate the really important stuff, the lion about to eat you, from the less important stuff, e.g., the sandwhich you ate last week. I think they act as a helpful epistemic trump card too: no matter what ideas you have about something, if X is a perceptual content, and contradicts those ideas, then our brains naturally give more credence to the perceptual/qualia laden representations. That is, consciousness is empiricist epistimology written into our brains.

    OK, enough speculation.

    Things that would kill this model: having qualia about something that is not ultimately sensory in some sense, perceiving things in the past or future. I haven’t really thought much about conscious recollection of things in the past. I tend to think of those as experiencing the sensory areas that are activated in the act of recollection, so a kind of feedback loop that takes over the normal perceptual machinery.

    As I said, I haven’t developed this all that much. Maybe I’ll make a post about it for people to smash around. I know philosophers like to swat down scientists foolish attempts at philosophy as much as scientists like to swat down philosophers foolish attempts at science.

  7. Peter Moleman

    Has anyone of read Thomas Metzinger “Being no one; the self-model theory of subjectivity”? Metzinger is a german philosopher with quite some knowledge of modern neuroscience. As far as I understand he argues that consciuosness and the related (or emerging) self do not exist as a thing but only as processes. He simply states that qualia do not exist and he makes a strong case for that argument. Although I am not able to follow all the arguments, because I have not matered all the basic neuroscientific facts, I think that he has gone beyond the theories of Dennett. Anyway, I think reading his work is neccessary for anyone who thinkes about consciousness and the self.

  8. Thanks for the reply Eric.

    According to your words you sympathize with Gerald Edelman´s model of recurrent or reentrant fedback loops of sensors (receptors) and actuators (e.g. body in general) interacting in the world, and with C. Koch´s idea that qualia simbolize the information or concious contents.

    But a little worry in the form of a question:
    Your theory of conciousness that you label as a type of cartesian materialism, suggest the idea that conciousness, as a perspectival model of the world, preexist before the self interacts with the world just because it frames the input, it is a process or…?

  9. Of course Metzinger´s book is a must for anyone interested in conciousness research.

    But i wonder why he has such a nihilistic sort of metaphysics about the self. Because if we analyze the concept of self in the area of philosophical psychopathology the question turns out to be: who is having a delusion?

  10. Eric Thomson

    I’m not sure about Edelman’s work: I have never been impressed with the little I have seen of it. My view is somewhat consonant with Koch, consistent with Baars.

    I’m not sure how to interpret your worry/question. I don’t have any developed view of what a self is, so I have no good idea how this PWM model of consciousness (Perspectival World Model)  relates to the self. Maybe a self will turn out to be necessary for the emergence of this PWM, maybe not.

  11. Dennett’s argument regarding the Cartesian Theatre (or rather Humean, as Hume started to use the theatre metaphor) is dead simple: there is nobody to watch the theatre, and I found absolutely no evidence in any Cartesian Materialism that could explain who watches. In other words, there is no way to get rid of humunculi – you get an infinite regress if you want to explain consciousness like that, or you are a dualist and you believe that there is a special substance called “thought” or something like that. Try to find neuroanatomical evidence for this! 😉

    Anyway, it might be as well a neuroanatomical fact that some parts of the brain are critical for consciousness or that they play the integratory role. But there is no reason to call them “theatre”. Note that on the neuroanatomical level you can go in two directions: (1) just use the textbook descriptions, messy and arbitrary as they are; (2) use neurofunctional theory of the brain. The problem is that we have only vague idea of (2) and (1) is not even a serious candidate for deciding any theoretical controversy as it is in need of confirmation itself. Frankly, all we have are parts and pieces, and we cannot say that functional thought experiments can be overthrown with neuroanatomical claims. They could be overthrown with neurofunctional theories – or partial theories. And one of the biggest problems in functional neurology is how much parallel processing the brain does. And how the serial consciousness comes into being from parallel processes.

    BTW, Metzinger’s book was recommended by Dennett.

  12. Hi Eric,

    Interesting that you should mention the Phi Phenomenon. Yes, I have looked into how the retinoid model explains this phenomenon. If you recall, in the retinoid model, selective visual attention consists in the projection of added neuronal excitation in retinoid space by selective excursions of the heuristic self-locus (HSL). Here’s how patterns of self-locus activation explain phi:

    1. When the first dot flashes on (S1), HSL moves to the spatial locus of S1.
    2. When S1 turns off and the second dot (S2) flashes on after a blank interval of ~ 30 ms up to ~200ms, HSL moves over intervening autaptic cells to the new spatial locus of S2.
    3. Over the trajectory of S1 to S2, neuronal HSL excitation plus excitation from the decaying S1 combine to create a moving trace of heightened autaptic cell activity.
    4. We see phi motion between successively flashed dots because there really is a path of moving neuronal excitation induced by the heuristic self-locus in the spatial interval between S1 and S2.

  13. Marcin Milkowski wrote:

    [Dennett’s argument regarding the Cartesian Theatre (or rather Humean, as Hume started to use the theatre metaphor) is dead simple: there is nobody to watch the theatre, and I found absolutely no evidence in any Cartesian Materialism that could explain who watches. In other words, there is no way to get rid of humunculi – you get an infinite regress if you want to explain consciousness like that…]

    It is true that if you posit *someone* watching a stage in a “theater” within the brain, you run into an infinite regress. This is the fatal error of thinking of the self as an observer. In my theoretical model of the cognitive brain, the self is *not* the *observer* of experience. Instead, the self is the unique spatial *origin* of all phenomenal experience (the stage of the theater). This is a critical switch in the conception of the self. Phenomenal experience, is completely constituted by neuronal activity within the retinoid system. Detection/observation of the neuronal representations in the stage of retinoid space is performed by specialized mechanisms (synaptic matrices) outside of the phenomenal sphere of the retinoid “stage” (i.e., in the “audience” of the theater).

  14. Eric Thomson

    I think Marcin’s version is a straw man I could also avoid.

    But Dennett’s formulation, as Arnold realizes, is much stronger, and would kill all sorts of plausible and interesting theories. His much stronger (and central) claim is (from CE):

    Cartesian materialism is the view that there is a crucial finish line
    or boundary somewhere in the brain, marking a place where the order of
    arrival equals the order of “presentation” in experience because what happens there is what you are conscious of.

    To the extent that this is even well formulated (he again falls into sloppy spatial and anatomical locutions when he only really cares about the functional story), it is a much stronger (or at least different) claim than ‘there is nobody to watch the theatre’. Of course nobody believes that, but the above exerpt is not equivalent to the anti-homuncular sentiments.

    At any rate, my original point was much more vanilla: taken as an anatomical claim, he is wrong. The functional stuff gets more wiggly and complicated.

  15. The claim that the dot is *perceived* to change its colors in ‘midstream’ in the phi example is not justified. What might be justified is the claim that most subjects *judge* that the color change occurs somewhere in the middle of the path of phi motion. I have experienced the phi paradigm with S1 a green dot and S2 a red dot and I am unable to tell where the change in phenomenal color occurs. If I were forced to express an opinion, the safe judgement of a central tendency would probably make me say “the color changed about halfway between the start and the finish of the motion”. I suspect that this is what the subjects in the original experiment did. If this is the case, it is not a real puzzle.

  16. Eric Thomson

     I am surprised that you dismiss it so casually. I haven’t been able to experience it myself either, which is one reason
    I criticized Dennett’s choice of this example. Nobody has done
    objective psychophysics comparing a dot actually moving and changing
    color to the phi phenomenon, to see if subjects can differentiate them. So we end up with questionable phenomenology from Dennett.

    Here is a phi demonstration as I said, I just don’t see it. I see a red dot, then a green dot, with a sense of movement for sure, and a sense that it is one dot that has moved, so when I think about it I judge that the dot must have changed color. But this is not what I see. Perhaps Dennett picked an example that happens to favor his own theory which would reduce experiences to judgments.

    I haven’t had a chance to play with his other illusion, the cutaneous rabbit illusion where when you are tapped on the wrist and elbow it feels something is moving up your arm, not just that you were tapped in two places. I haven’t experienced this one, but perhaps it actually happens. There was a very interesting study of the cutaneous rabbit using fMRI recently (study here). If this works, then it is the somatotopic analog of the phi phenomenon. Interestingly, the same thing doesn’t seem to happen visually. Tap the retina in one location with a localized light, and then another location, and we don’t see a light dancing across the eyes.

    I think a better example in the visual system might be the flash lag effect. Not a super impressive phenomenon phenomenologically, but interesting.

  17. It doesn’t have to be “someone” to have infinite regress. All it takes to have infinite regress is that the “watcher” is not explained away.
    If the self is the origin of experience, you could avoid this problem. But if you say it is a spatial (why not a spatiotemporal?) origin, then I don’t get it. The theatre is its own origin. You think it can possibly explain anything? Sounds pretty impressionistic if you take it literally. But you seem to attach the metaphor to something pretty different.

    The problem is that (1) most functionalists, incl. Dennett, would agree that there are neuronal activities that realize the conscious experience, so it’s easily granted that the mechanism could be located spatially somewhere; it could even be retinoid system; (2) detection (or micro-takings, or whatever) is also presupposed by many theorists, and it’s not really connected with the theatre metaphor.

    Now the difference is when you speak about the origin of experience (constitution or whatever). It’s absolutely critical that you define this in details — otherwise it’s just saying “and here consciousness emerges”. Not really informative.

    My problem is that when you decant the theatre metaphor like you do, there is almost nothing left. Your model is a decent functionalist, information-processing model of consciousness. You will have to learn to live with that 😉

  18. If you think of it, you’ll see that we take anatomical claims to be spatial but Dennett’s claim is more spatiotemporal, or even temporal. That’s why Libet’s experiments are important.

    BTW, you experience the phi phenomenon all the time when watching the movie. After all, it’s 25 frames per second, and you perceive movement (that’s another kind of phi phenomena). In movies, you rarely have strange temporal reversal which is what Dennett want to stress. The temporal aspect of consciousness is absolutely crucial.

    Anyway, phi phenomena were confirmed and observed in Gestalt psychophysiology

  19. The retinoid system does constitute a spatiotemporal neuronal space. I emphasized the spatial aspect of it because the self is the spatial *coordinate of origin* against which all events in other coordinates of retinoid space are referred. This provides a perspectival egocentric phenomenal space in the brain (our intimate experience of the world). Also, as I mentioned earlier, in this theory the watchers/observers are the specialized neuronal mechanisms that detect, classify, and perform semantic analysis of objects, features, and events that are represented by the patterns of neuronal activity within retinoid space. The minimal neuronal design of these mechanisms and systems is detailed in my book *The Cognitive Brain* (TCB).

    Can the retinoid model explain anything worth explaining? Sure it can! If you read TCB, you will see how the structural and dynamic properties of the retinoid model explain many psychological observations that were not previously understood.

    I have not “decanted the theatre metaphor”; what I have done is to show that the detailed structure and dynamics of a particular system of neuronal mechanisms (the retinoid system) has the representational competence to warrant the metaphorical notion of a *theater of consciousness”. The challenge for other theorist is to demonstrate that different kinds of biological mechanisms perform as well as or better than the retinoid model.

  20. Eric, the flash lag effect shown in that nice link you provided gives us a good opportunity to contrast a functional explanation with a mechanistic explanation. Here’s the explanation that went along with the demonstration in the linked web page:

    “The explanation, in a nutshell: Our mental perception and planning mechanisms need to take into account the delays in afference, computation & efference. Thus moving objects are “perceived” a bit ahead of their assumed trajectory; the flash (being essentially stationary) is not. Consequently, one perceives a positional disparity between briefly flashed stationary and moving objects.”

    Here is my explanation based on the operating characteristics of the retinoid mechanism:

    The circular trajectory of the black ring containing a blue disc is evoked spatiotopically among corresponding neurons in retinoid space. When we track the trajectory of the disc, the heuristic self-locus (HSL) leads the stimulus input coordinates, thus priming leading cells in retinoid space and shifting the phenomenal spatiotopic locus of the disc slightly ahead of its input locus. When the yellow disc is briefly flashed it is perceived as lagging the blue disc because its leading cells in retinoid space have not been primed and its representation is not shifted ahead. The extent of lag is perceived to increase with the speed of rotation because HSL leads the rotating stimulus by a greater extent as speed increases. An examination of the neuronal structure and dynamics of the retinoid mechanism provides a causal justification for the perceived lag.

    An interesting aspect of the retinoid model is that it successfully predicted a new illusion. I have called it the pendulum illusion. If a figure in lateral reciprocal motion is viewed through a triangular aperture in an opaque screen, it is perceived to swing like a pendulum pivoting at the apex of the triangular aperture (see The Cognitive Brain, p. 239 and Fig. 14.5 for more details and an explanation of this illusion).

  21. Eric Thomson

    Marcin: I haven’t seen a good paper on Phi  that wasn’t just impressionistic phenomenology. The Gestalt psychologists did some wonderful work, but the phi phenomenon is diaphanous.

    Your point is good that we see apparent motion all the time in movies, but that is consistent with a Cartesian Materialism (as is phi for that matter).

    I would take something to be inconsistent with Cartesian Materialism if we saw temporal effects that were outside a window of, say 500 ms (this is just a ballpark guess at the temporal window of integration used to build the model of the world that is experienced). Libet’s experiments are hard to interpret on many levels, but if you wrote something up about it it would be good to have something concrete to argue about.

    And of course all this is tangential to my very simple claim in this post which is ultimately also tangential to Dennett’s point, despite the way he sometimes wrote and the way he is often interpreted.

  22. Eric Thomson

    Assume there exists a psychological/functional model of a set of neurons that lets me predict the qualia of a subject at time t. By ‘qualia’ I mean the occurrent contents of conscious experience.

    So it gets the temporal order right (it predicts a subject experienced a sunset before a c-sharp, not at the same time, not in the opposite order).

    Is that enough for the model to be a Cartesian Materialist model? I.e., would it imply a functional subsystem exists “where the order of
    arrival equals the order of “presentation” in experience because what happens there is what you are conscious of”? I am not sure. I have never liked Dennett’s characterizations of the Cartesian Theatre. For instance, I wouldn’t want to say the subject is conscious of what is happening there: what is happening there is what is conscious! (You can you can characterize ‘what is happenign there’ either functionally or neurally depending on your philosophical stripes.) Qualia(t) supervene on the state of this functional subsystem at time t. Assume, for example, that for visual consciousness this system builds a model of the bits of the world causing present retinal activity. The contents of this model at time t are the contents of consciousness at time t. This doesn’t imply that the mechanisms that go into this model ignore past activity: it just means that the construction of the present model depends on the past. This wouldn’t be surprising: obviously we experience motion and the like so there has to be a window of integration there for the construction of this model.

    I’m not saying the details of my model of consciousness mentioned above is right, but it is plausible, and it is a Cartesian Theatre. The fact that it happens to jibe with our phenomenological intuitions is only a nice consequence. I look at it as an asset of a model if the autophenomenology and heterophenomenology match up.

    This is all very abstract. If you had a specific example of a phenomenon where there are lots of details about the experimental parameters (e.g., what timing relations must exist among stimuli to get apparent motion or the cutaneous rabbit illusion), we could have a much more productive argument.

  23. How about this example adapted from my recent paper in *Consciousness & Cognition* (2007)?

    Subjects sit in front of an opaque screen having a long vertical slit with a very narrow width, as an apeture in the middle of the screen. Directly behind the slit is a computer screen, on which any kind of figure can be displayed and set in motion. A triangular-shaped figure in a contour with a width much longer than its height is displayed on the computer. Subjects fixate the center of the aperture and report that they see two tiny line segments, one above the other on the vertical meridian. This perception corresponds to the actual stimulus falling on the retinas (the veridical optical projection of the state of the world as it appears to the observer).

    The subject is given a control device which can set the triangle on the computer screen behind the aperture in horizontal reciprocating motion (horizontal oscillation) so that the triangle passes beyond the slit in a sequence of alternating directions. A clockwise turn of the controller increases the frequency of the horizontal oscillation. A counter-clockwise turn of the controller decreases the frequency of the oscillation. The subject starts the hidden triangle in motion and gradually increases its frequency of horizontal oscillation.

    Results:

    As soon as the figure is in motion, subjects report that they see, near the bottom of the slit, a tiny line segment which remains stable, and another line segment in vertical oscillation above it. As subjects continue to increase the frequency of horizontal oscillation of the almost completely occluded figure there is a profound change in their experience of the visual stimulus. At an oscillation of ~ 2 cycles/s (~ 250 ms/sweep), subjects report that they suddenly see a complete triangle moving horizontally back and forth instead of the vertically oscillating line segment they had previously seen. This perception of a complete triangle in horizontal motion is strikingly different from the tiny line segment oscillating up and down above a fixed line segment which is the real visual stimulus on the retinas.

    As subjects increase the frequency of oscillation of the hidden figure, they observe that the length of the base of the perceived triangle decreases while its height remains constant. Using the rate controller, the subject reports that he can enlarge or reduce the base of the triangle he sees, by turning the knob counter-clockwise (slower) or clockwise (faster).

    These experiments demonstrate that the human brain has internal mechanisms that can *construct* accurate analog representations of the external world. Notice that when the hidden figure oscillated at less than ~ 2 cycles/s, the observer experienced an event (the vertically oscillating line segment) that corresponded to the visible event on the plane of the opaque screen. But when the hidden figure oscillated at a rate greater than 2 cycles/s, the observer experienced an internally constructed event…

  24. Eric Thomson

    Arnold. I like this example: is there an example online?

    I would be curious to see what Marcin thinks is a good example that Cartesian Materialism can’t explain.

  25. Seeing-more-than-is-there (SMTT): Part 2.

    This is a continuation of my previous post.

    The experimenter asks the subject to adjust the base of the perceived triangle so that the length of its base appears equal to its height.

    Results:

    As the experimenter varies the actual height of the hidden triangle, subjects successfully vary its oscillation rate to maintain approximate base–height equality, i.e., lowering its rate as its height increases, and increasing its rate as its height decreases.

    This experiment demonstrates that the human brain has internal mechanisms that can accurately track relational properties of the external world in an analog fashion. Notice that the observer was able to maintain an approximately fixed one-to-one ratio of height to width of the perceived triangle as the height of the hidden triangle was independently varied by the experimenter.

    These and other empirical findings obtained by this experimental paradigm were predicted by the neuronal structure and dynamics of a putative brain system (the retinoid system) that was originally proposed to explain our basic phenomenal experience and adaptive behavior in 3D egocentric space (Trehub, 1991). It seems to me that these experimental findings provide conclusive evidence that the human brain does indeed construct analog representations of the external world within a coherent and perspectival egocentric neuronal space (the “stage” of conscious content in the Cartesian “theater”).

    Eric, I have not seen any online examples of SMTT.
    However, the phenomenon can usually be seen by using a crude apparatus. Take a sheet of stiff gray poster board and cut a vertical slit about
    2 mm wide in the center of the board. Take another narrower sheet of poster board and draw a black outline of a figure with a height less than the height of the slit, and a width of ~ 18 mm. Fixate the center of the slit and slide the figure laterally behind it, back and forth so that the figure goes just past the slit in both directions. When the rate of alternation exceeds ~ 2 cycles/s, you should suddenly see a complete figure somewhat compressed in width. If you try it out, let me
    know if it works for you.

  26. Eric Thomson

    Arnold: thanks. As you probably saw in my ‘PWM’ post, your model strongly influenced the direction I went, as it let me see the ‘perspectivalness’ of consciousness as the ‘perspectivalness’ of egocentric spatial coordinates, which I thought because of your book.

  27. Malcolm Dean

    It’s important to remember that Descartes’s problem was theological. He had to defend the idea that there is an essential difference between humans and animals. Since they both have brains, which in a few cases are even larger than ours, he had to maintain a place in his theory for non-physical thought.

    Second, there is no place in the nervous system where it “all comes together” because it is all a set of networks physically structured by Cable Theory, just like any complex information or energy network. If there existed a central module or “seat of the soul” (in more ancient parlance) dictators such as Stalin would have found it by now, because it would suit their purposes admirably.

    Theater is art and artifice. Trying to find activities of mind which suit a Cartesian prejudice (which, to repeat, is theological in origin)is not to search for anything essential about mind or brain. In Buddhist philosophy, such ideas are viewed as transitory, emergent, and ultimately illusory — as the apparently interminable philosophical discussions of Descartes
    will prove to be. 🙂

  28. Nightvid Cole

    Here’s another interesting one: the “inverse blink” phenomenon. (An “inverse blink” is when your eyes are closed, you open them very briefly only to close them again) . One thing I noticed is, if looking in a direction without objects closer than about 2 feet (0.6 m) or so, a “snapshot” of your surroundings obtained in an inverse blink appears 2-dimensional if the inverse blink is sufficiently short and preceeded and followed by closed eyes for at least a couple seconds. (Try it: while walking along outside or down a hallway with your eyes closed, take inverse blink “snapshots” every couple seconds, and make them as short as you possibly can. Despite allowing you to avoid bumping into things, these “snapshots” will seem 2-d to you, with no depth at all.)

    Now here’s the interesting part: Lengthen your “inverse blinks” until you see depth again. It will then *seem* to you (At least if you’re like me) as if the depth in the “snapshot” had been there from the moment you opened your eyes, rather than being “imposed” upon a flat image a brief instant later. The “orwellian” explanation would be, you first saw a flat image, but your memory of that was erased and replaced by an image containing depth. The “Stalinesque” explanation would be, when the image first arrives at your visual cortex, your brain “waits” for 100-200 msec to see if depth information becomes available. If it doesn’t, it “gives up” and passes along the 2-d image to your consciousness, but by that time your eyes are already closed again. If it DOES get depth information, it passes along only a “fully formed from the beginning” 3-d image to your consciousness.

    I discovered this phenomenon on my own by accident when walking down hallways with my eyes mostly closed to recover from severe eye strain I got in the office. Since I haven’t yet gotten anyone else to try it, tell me if you get the same results as me (if you don’t mind)

  29. I think you would have the same experience without blinking if you are in a dark hallway that is illuminated intermittently by a low-intensity strobe light. No need for the Orwellian and Stalinesque metaphors when you experience depth with the longer exposure. The short-term memory pattern of autaptic cell-activity in retinoid space (the *extended present* in your phenomenal field) insures that your most recent ~250 ms of 3D-retinoid activity will determine your perception.

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