Re: An Auditory Illusion (Al Bregman )

Subject: Re: An Auditory Illusion
From:    Al Bregman  <bregman(at)HEBB.PSYCH.MCGILL.CA>
Date:    Fri, 16 May 1997 16:31:54 -0400

May 16, 1997 Dear Dick and List I have another comment on your demonstration of the separate habituation of left- and right-side words cycling a half-step out of phase. I guess you never considered the religious significance of your finding. Let me point it out. I think that the problem of maintaining of two concurrent mental representations connects with a larger problem in cognition, namely what the neural basis is for recognition and representation. The dominant view in cognitive psychology is that the representation of an abstract entity (a word, for example) is nothing more than a node (engram, cell assembly) and that recognition is simply the activation of that representation. But consider the following two cases: 1. One sees a red ball on a blue table. 2. One sees a blue ball on a red table. According to a "node" theory, in both cases the nodes representing red, blue, ball, on and table are activated. What then is the difference? The two cases require a different arrangement of the same ideas, but node-based theories cannot express this. A computational system that used symbols could arrange them in two structures as follows. Structure 1: (RED colour-of BALL) ON (BLUE colour-of TABLE). Structure 2: (BLUE colour-of BALL) ON (RED colour-of TABLE). Notice that the symbols are ones that were already in the system: red, blue, on, etc,, but the symbolic structures are new and unique for each case. This is easy for a symbol-manipulating system to do, but it is not clear to me how it is possible for a node-based system to form momentary structures that combine concepts to represent unique events, and then dissolve these structures and form new ones as the situation changes. There is a similarity to your two concurrent voice situation. A symbol-manipulating system would have no trouble in forming two structures: Structure 3. (VOICE at LEFT) SAYS X - where X is a particular word Structure 4. (VOICE at RIGHT) SAYS X However, a node-based recognition system would have to fire the nodes VOICE, SAYS, LEFT, RIGHT, and X. According to the preceding argument there is no node-based mechanism (that I know of) that can say X is simultaneously at the left and at the right. Even if the words at the left and right were *different* (X and Y), there would be a firing of nodes VOICE, LEFT, RIGHT, SAYS, X, AND Y, with no structure to say which word was on the left and which on the right. Node theory has problems because it fails to make a distinction between types and tokens. Types are the general concepts, such as LEFT and VOICE. Tokens are elements that refer to them but are free to bind into structures. There can be as many tokens as you want referring to a specific type, so you can have the same token more than once in a given structure; e.g., Structure 5. (RED color-of TABLE) on (GREEN color-of TABLE). where TABLE is used twice. Even if node theory could think up some way of binding the WORD-X node to *both* LEFT and RIGHT nodes, there would still be only a single WORD-X node. I can't imagine how this one node could tire at two different rates. On the other hand, two separate symbolic structures (i.e., descriptions) *could* tire at different rates. It is generally accepted that node-based recognition systems are the only ones that are adequate models of the brain's recognition capacity, as distinct from recognition by computer. If this is true, your data prove that the brain as we know it could never form representations that both minds and computers can do with ease. This is important for philosophy and surely for religion. Computers would have to be allowed into heaven, but not brains. Al

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Electrical Engineering Dept., Columbia University