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Date:         Mon, 24 Nov 1997 01:19:47 +0000
Reply-To:     "PSYCHE Discussion Forum (Biological/Psychological emphasis)"
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Sender:       "PSYCHE Discussion Forum (Biological/Psychological emphasis)"
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From:         Aaron Sloman <[log in to unmask]>
Subject:      Re: Baars on Binocular Rivalry (was Re: Illusions)

Thanks Bernie, I don't know how you find all the time, and I am not sure I can keep up, but here goes. (I still owe Stan Klein a reply, explaining the difference between being meaningless and having no clear meaning, to come later...) I'll separate out several different claims about the requirement for coherence in perception, and argue against them, while supporting a loosely analogous argument about the strong likelihood of resource limits in higher level parts of the architecture for an intelligent agent. The problem of resource limits could be confused with a requirement for a consistency constraint. > Date: Sat, 22 Nov 1997 00:25:53 -0500 > From: "<Bernard Baars>" <[log in to unmask]> > > Aaron thinks we can have internally inconsistent perceptual experiences. Here > is the test. > > CAN YOU SHOW THAT A PERSON CAN PERCEIVE TWO SOLID VISUAL OBJECTS IN THE SAME > PERCEIVED SPATIAL LOCATION AT EXACTLY THE SAME PERCEIVED TIME? OK, we now have three distinct theses of diminishing strength: 1. When retinal inputs differ one or other will be suppressed unless they fuse into a single percept as in normal stereo vision. That strong thesis seems to believed by many people and that's what I read into page 89 of B.Baars "In the Theater of Consciousness" (OUP 1996). It now seems that we are agreed it is false, so you didn't mean to say what your words seemed (to me) to be saying. Then came this less strong thesis: 2. Consciousness reflects an internal consistency constraint. I assumed this weaker thesis was an attempt to rule out combinations in which different, inconsistent, things are perceived in the same portion of the visual field. There are various counter-examples discussed in my previous messages, and many more: e.g. a motion after-effect in which perception of upward motion occurring at a particular location coincides with perception of only static objects there. But you didn't want to accept the things I listed as counter-examples, so I suggested that perhaps nothing could be a counter example and the claim is therefore non-empirical. You've now responded with a third, still weaker thesis. (NB: "weak" does not mean "bad". It's just a neutral description of the number and diversity of consequences of the thesis.) 3. A person cannot "PERCEIVE TWO SOLID VISUAL OBJECTS IN THE SAME PERCEIVED SPATIAL LOCATION AT EXACTLY THE SAME PERCEIVED TIME" This weakest thesis is still interesting, but I am not sure whether it's true or false or perhaps just a non-empirical piece of mathematics or logic. My initial reaction is that it is false, like the simplistic interpretations of the first two theses, since, for instance, Picasso in one of his sculptures showed us how to see a sports car and a baboon's head in the same place at the same time. Michaelangelo encouraged a percept of a human body struggling to emerge from a block of marble. I don't think we are invited to see the marble as *enclosing* a separate body. That would be a far less powerful work of art. Or consider the well known fruit-face: assemble a pumpkin, a banana, a couple of cherries and a carrot in the appropriate configuration, with the help of some adhesive, and then you can see in the same place at the same time a smiling face with two eyes a nose and a mouth, and a collection of different items of fruit: two solid visual objects in the same perceived spatial location at exactly the same perceived time. Perhaps you'll say those are not counter examples to thesis 3, since in each case we see the same 3-D bounding surface but can apply different inconsistent classifications to it simultaneously. Can you actually describe in any detail a type of perception which you would accept as a counter example if it were to be produced in some carefully contrived experimental situation? If not, perhaps that's because what you are ruling out is actually something incoherent. I.e. it's not a fact about the brain that it can't do it, just as it's not a fact about the brain that it can't make the number 27 a prime number. For example, suppose that by "solid" you really meant "opaque" (i.e impervious to vision). and by "two objects" you really meant "differently shaped objects". E.g. you are asking (for example) can a person see an opaque cube and an opaque sphere in the same perceived spatial location at exactly the same perceived time". Unfortunately, the problem now is not an empirical question about what the brain can or cannot do but a conceptual question about what it could mean for two differently shaped objects to occupy exactly the same location. If their shapes are different they certainly cannot: if a solid object occupies all and only the same spatial locations as a cube then it must be a cube, not a sphere. But that's a trivial (well, nearly trivial) matter of definition, not a fact about what brains can and cannot do. Or, to be more precise: it's a fact of mathematics (geometry) not a fact of biology (brain science). But perhaps you meant something like this: can a person see two opaque solid objects in roughly the same place, i.e. with overlapping volumes, e.g. Michaelangelo's human bodies struggling to emerge from blocks of marble, with which they somehow co-occur. You seem to say No, whereas I expect the answer is yes: provided the person, the context, and the stimuli are right. But in any case, it is very hard to reach a negative conclusion from any number of experiments. Imagine trying to prove by experiment that no human brain can find a proof of Fermat's last theorem. Millions of negative experimental results would still not give an answer to the question, which we now know is positive. Or imagine experiments prior to Einstein&Minkowski seeking to find out whether a person can imagine curved 3-D space, or instantaneous events which are not unambiguously ordered in time, or... Human brains are the most creative machines known to science, and any generalisation about their limitations needs to be treated with *extreme* caution. (Even that one...) But I now have to ask, does this consistency/coherence constraint really add anything significant to theories of perception or consciousness? Why is it felt to be important? Is it just a relic of a rationalist view of mind, taken by granted by many philosophers (even Dennett, in weak moments)? Maybe one of the most important things about (human) brains is that they can transcend what's consistent, coherent, rational, etc. Why? Because at some stage evolution produced a powerful mechanism (I don't necessarily mean a computational mechanism) for assembling new information structures out of old ones, and then found all sorts of deep ways to make use of it, or variants of it. E.g. it's crucial to planning and much problem solving, and to communication in natural language. It makes mathematical learning and problem-solving possible. But, for deep mathematical reasons, it is hard or impossible to combine such combinatorial creativity with a guarantee of consistency, and sure enough humans are frequently seduced by incoherent thoughts, objectives, ethical systems, religious propaganda, etc. So why not incoherent percepts too, including visual percepts? Some people used to think the reason was that visual percepts employed spatial forms of representation, and spatial representations cannot represent what is spatially impossible. We now know that is false: examples include the Penrose triangle, Richard Gregory's 3-D implementation of it, Escher figures, and one of my own favourites: _______________________________ i.e. a round square seen edge on. NB: the Penrose/Escher figures (e.g. impossible triangle) are not illusions or simply ambiguous figures. Rather they are locally consistent projections of globally inconsistent 3-D structures. When the picture is sufficiently complex, e.g. not a triangle but a decagon, many people will see only the local consistency, and not detect the global inconsistency: i.e. they will see a geometrically impossible/incoherent object. (Does that refute the consistency/coherence theory?) So why struggle to defend such an embattled theory, as the theory that the contents of consciousness must be coherent? I think it's a confusion of a processing issue with a content issue, to be explained later. Of course, the creativity of each brain is limited, but the limits change over time. History is littered with the corpses of ideas about what is incoherent, inconceivable, impossible: the earth moving through space, space-filling one-dimensional curves, everywhere continuous but nowhere differentiable functions, sets which are in one to one correspondence with proper subsets of themselves, the square root of a negative number, adding light to light in order to produce darkness, humans evolving from micro-organisms, distant events being both before and after each other, force-fields in totally empty space, curvature of 3-D space, transmission of music or pictures across empty space, something behaving as both wave and particle, ... to mention a few of the better known cases. Instead of stressing the requirement for contents of consciousness to be coherent, consistent, etc. we should perhaps be trying to understand what sorts of mechanisms can fruitfully push their own boundaries beyond what till then are the limits of consistency. That is what many great scientists, mathematicians and artists have done. Maybe every child does it as part of its normal process of development, until we use bad schools and bad scientific text books and religious dogma to stifle the process. Anyhow, I am perfectly aware that this is hand-waving. The real work remains to be done. Let's just not shut out theories because so far no established evidence seems to support them, if there's a strong theoretical reason for accepting them (in this case the theory that perception, like thought, involves combinatorial creativity, at least in some animals. Maybe not house flies?). > My reading of > all the research going back to Helmholtz is that the answer is no. Until recently all the evidence was that nobody could prove Fermat's last theorem. There were probably even more failed attempts at that task than psychological experiments on perception of inconsistent scenes. > All the > claimed exceptions to the rule involve a clever visual-brain solution to the > problem, We seem do be agreed on the essential creativity (cleverness) of perceptual mechanisms? > as in the case where we perceive a hand over one eye as a > diaphanous, filmy object, THROUGH WHICH we see another object. The visual > brain is just brilliant in solving such conflicting inputs. Given all that, what are the mechanisms underlying such brilliance? My conjecture is that they depend on combinatorial creativity. And given that, why should such creativity be constrained to fit any particular kind of coherence criterion? And how could it be? (It's not always easy to build semantic constraints into the syntax of a powerful form of representation.) > Most of the time, > in normal vision, the dominant eye's interpretation "wins," though the > nondominant eye provides a sense of depth. (I must be a mutant: my eyes are symmetric on this test.) I think that if you abandon this (arbtrary?) consistency constraint it will enrich your theory of consciousness, make it closer to the facts, and I suspect make it easier to produce explanatory mechanisms. > I think Aaron is entirely right that local or peripheral hypotheses about > such conflicting input situations don't get us very far. It's a > multi-layered, if-one-thing-doesn't-work- try-another system, not at all > "boring." I apologise for the rhetorical flourish. Boringness is less important than truth. Or, as J.L.Austin said, truth is more important than importance. > So the theoretical claim is that the consistency constraint applies not just > to vision, not just to audition and the other senses, but to "conscious" or > "explicit" ideas, meanings, and probably dominant intentions as well. I give > a whole bunch of additional evidence for this general claim in my 1988 book. I think it is important, as hinted above, to distinguish two distinct claims: (A) the contents of vision, consciousness, audition (motivation, ?) etc. are constrained to be consistent. (I think this is false.) (B) The mechanisms involved in self-awareness and in deliberation and reasoning (or other things using a "global workspace"?) are inherently resource limited. I.e. they can't simultaneously perform arbitrarily many distinct, unrelated, tasks. As far as (B) is concerned, I think it is true, for deep engineering design reasons to do with the impossibility of implementing physical mechanisms which violate it in a well integrated system. Reasons for the resource limits restricting parallelism (and thereby incidentally increasing coherence) include the following: (1) processes involving combinatorial exploration require repeated re-use of the same temporary storage space. (2) the high level processes use a long term content addressible memory, which needs to use all available parallelism for optimising retrieval speed, at the cost of ruling out answering different questions concurrently (since cross-talk ccould result). (3) An argument I first heard from Dana Ballard: various learning tasks explode exponentially if too many things are done in parallel (e.g. finding which subset of N concurrent actions produced some effect, potentially requires considering and testing 2 to the power N possible subsets, and it gets MUCH worse if delayed consequences are allowed). I.e. (B) is not just an empirical fact about human consciousness, but something deper. It could apply to robots, martians, etc. However the status of (A) is different: checks and constraints preserving consistency have great heuristic power, and therefore we can expect to find them in many places. However, since they are hard to implement in general, and since an apparent contradiction may be an important first clue towards an expanded conceptual framework giving access to a deeper more general ontology, as often happened in the history of science and mathematics, we should not expect the consistency requirement to have any sort of ABSOLUTE status. I.e. exceptions can occur, and may be an important part of learning or development. For me, perhaps the most compelling evidence that human vision does not rigidly exclude inconsistent or incoherent percepts are the motion after-effects in which one sees simultaneously motion, and nothing moving, in the same location. > On theory, Aaron claims all ideas we have today are computationally > inadequate. I didn't say "computationally inadequate". Computation is but one form of information processing though its boundaries are somewhat ill defined. (Does it include continuously varying systems, which are non-computational in the sense in which computation requires a succession of discrete states.) When I talk about information processing mechanisms I leave open the possibility of including mechanisms that are as different from today's computational mechanisms as the latter were different from the cogs, levers and strings of yesteryear. > That may be true. People like Stan Franklin are working to push > that envelope. Stan's work is certainly an interesting example of a raft of explorations of architectures for intelligent agents. (I have my own pet models too.) But I suspect all this work will turn out to be missing something very powerful, which is still waiting to be discovered. (NB It has nothing to do with Godel's theorem, which I think is a complete red herring.) > As a person concerned primarily with evidence, I'm initially > interested in EMPIRICAL adequacy. Then we have to try to fix problems of > ALGORITHMIC adequacy. There are lots of examples in the other sciences that > have worked just like this, where the mathematical algorithm became available > after the evidence was reasonably well understood conceptually. I personally prefer the approach of great physicists, like Newton and Einstein: First (by inspired guesswork) produce a great new theory of the architecture of the world, accounting for a wide range of already known phenomena, and absorbing the best previous theories as special cases, possibly inaccurate special cases. Then work out its new consequences with as much mathematical precision as possible. Then do experiments, etc. to see how the consequences fit reality, and where they don't fit, be prepared to modify the theory, or consider alternatives. If all the consequences are too vague or ambiguous to allow any refutation then don't necessarily throw the theory away as unscientific: try to sharpen it. Algorithms provide just one sort of detail within the framework of an architecture: don't be too impressed by them. Nowadays any theory of adequate richness is likely to be too complex for consequences to be derived without simulation. If simulation is impossible, start worrying about whether that's because the theory is too ill defined. Enough. I've gone on too long again. Cheers. Aaron

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