PHayes@SRI-KL (Pat Hayes) (07/02/86)
Mozes long review of Kelleys book "The Evidence of the Senses" tells one a lot about the book. In particular, it sounds as though it makes the same basic mistake about representations that many other 'anti-computationalist' philosophers , including Gibson and his followers, make. The 'representatonalist' account of perception does NOT claim that instead of perceiving the world, we perceive internal representations of the world. That would indeed be a position with many difficulties. Rather, it says that the WAY we perceive the world is BY making representations of it. The data structures are, to put it simply, the output of the perceptual process, not its input. The question the representational position must face is how such things ( representations ) can serve as percepts in the overall cognitive framework. While there are indeed many problems here, the position is not as silly as Gibson thought it was. Pat Hayes -------
eyal@wisdom.BITNET (Eyal mozes) (07/10/86)
> The > 'representatonalist' account of perception does NOT claim that instead of > perceiving the world, we perceive internal representations of the world. > That would indeed be a position with many difficulties. Rather, it says > that the WAY we perceive the world is BY making representations of it. > The data structures are, to put it simply, the output of the perceptual > process, not its input. I would agree with Gibson (and with Kelley) that this boils down to the same thing. The "output" of perception (if such a term is appropriate) is our awareness. Realists claim that this awareness is directly of external objects. Representationalists, on the other hand, claim that we are directly aware only of internal representations, created by a process whose input are external objects; this means that we are aware of external objects only INDIRECTLY. That is the position Gibson and Kelley argue against, and I think they do understand it accurately. Note that the above applies only to PERCEPTUAL representationalists. It does not apply to COGNITIVE representationalists, who may agree that perception is direct, but claim that internal representations are then formed for the purpose of conceptual thinking. Gibson claimed that concept-formation is direct as well; but on this point, Kelley disagrees with him (this is indicated by his discussion of the issue in chapter 7 of "The Evidence of the Senses"; by his paper "A Theory of Abstraction", published in "Cognition and Brain Theory", vol. 7, no. 3 and 4, Summer/Fall 1984; and by his references to Ayn Rand's "Introduction to Objectivist Epistemology"). Eyal Mozes BITNET: eyal@wisdom CSNET and ARPA: eyal%wisdom.bitnet@wiscvm.ARPA UUCP: ..!ucbvax!eyal%wisdom.bitnet
sher@ROCHESTER.ARPA.UUCP (07/12/86)
In article <8607100457.AA12123@ucbvax.Berkeley.EDU> eyal@wisdom.BITNET (Eyal mozes) writes: >The "output" of perception (if such a term is appropriate) is our >awareness. Realists claim that this awareness is directly of external >objects. Representationalists, on the other hand, claim that we are >directly aware only of internal representations, created by a process >whose input are external objects; this means that we are aware of >external objects only INDIRECTLY. That is the position Gibson and >Kelley argue against, and I think they do understand it accurately. I may be confused by this argument but as far as visual perception is concerned we are certainly not aware of the firing rates of our individual neurons. We are not even aware of the true wavelengths of the light that hits our eyes. We have special algorithms built into our visual hardware that implements an algorithm that decides based on global phenomena the color of the light in the room and automatically adjusts the colors of percieved objects to compensate (this is called color constancy). However this mechanism can be fooled. Given that we don't directly percieve the lightwaves hitting our eyes how can we be directly percieving objects in the world? Does percieve in this sense mean something different from the way I am using it? I know that for ordinary people the only images consciously accessible are quite heavily processed to compensate for noise and light intensity and to take into account known facts about the tendencies of objects to be continuous and to fit into know shapes. I don't know how under such circumstances we can be said to be directly aware of any form of visual input except internal representations. My guess is that you are using words in a technical way that has confused me. But perhaps you can clear up this.
eyal@wisdom.BITNET (Eyal mozes) (07/19/86)
David Sher writes: >I may be confused by this argument but as far as visual perception is >concerned we are certainly not aware of the firing rates of our individual >neurons. We are not even aware of the true wavelengths of the light that >hits our eyes. We have special algorithms built into our visual hardware >that implements an algorithm that decides based on global phenomena the >color of the light in the room and automatically adjusts the colors of >percieved objects to compensate (this is called color constancy). However >this mechanism can be fooled. Given that we don't directly percieve >the lightwaves hitting our eyes how can we be directly percieving objects >in the world? That's exactly the point. We DON'T perceive lightwaves, images or neuron firing-rates; we directly perceive external objects. The light waves, our eyes, and the neural mechanisms (which are MECHANISMS, not algorithms) are not the objects of our perception; they are the MEANS by which we perceive objects. This will seem implausible only if you accept the diaphanous model of awareness. Stephen Barnard writes: >Consider what happens when we look at a realistic >painting. We can, at one level, see it as a painting, or we can see >it as a scene with no objective existence whatsoever. How could this >perception possibly be interpreted as anything but an internal >representation? Sorry, I can't follow your argument. Of course, a realistic painting is a representation; but it is not an INTERNAL representation. Gibson's books do contain long discussions of paintings; but he specifically distinguishes between looking at a painting (in which case you are perceiving a representation of the object) and directly perceiving the object itself. >Gibson emphasized the richness of the visual stimulus, >arguing that much more information was available from it than was >generally realized. But to go from this observation to the conclusion >that the stimulus is in all cases sufficient for perception is clearly >not justified. Gibson did not deny that there are SOME cases (for example, many situations created in laboratories) in which the stimulus is impoverished. His point was that these cases are the exception, rather than the rule. Even if we agree that in those exceptional cases there is some inference from background knowledge, this doesn't justify concluding that in the normal cases, where the stimuli do uniquely specify the external object, inference also goes on. Since I can't possibly do justice to these issues in a short electronic message, let me repeat my recommendation of Kelley's book. It discusses all these issues in detail, and presents them very clearly. I'm sure it will be of great value even to those who'll end up disagreeing with its conclusions. Eyal Mozes BITNET: eyal@wisdom CSNET and ARPA: eyal%wisdom.bitnet@wiscvm.ARPA UUCP: ..!ucbvax!eyal%wisdom.bitnet