A propos Pat Hayes' posting of May 11 concerning the elusive "now". I share his bewilderment and agree that "there is something very peculiar about time" . I think a partial--but only partial--answer to the problem of the puzzle of the perceptual NOW is the realization that the metaphor of the "dot moving along a line", or a bullet traveling through the phase space of brain dynamics, is flawed. The fallacy can be appreciated when we ask what is the content of a moment in consciousness. Unlike the point in phase space that always defines a complete present state, the state of my consciousness at this instant has no meaning. If you could stop time, or momentarily stop all neural activity, the instant is likely to have no conscious content. It takes ongoing neural activity; consciousness straddles time, both past, present and future being contained in my consciousness. I think that Jeffrey Gray (Tucson II) was wrong when he said that consciousness cannot affect ongoing behavior because it comes too late. He cited the tennis player who cannot wait for the latest sense impressions to reach consciousness. Per contra, I claim that the tennis player is very much aware of the position and stroke of his opponent several hundred milliseconds ago, he has already computed ahead where and how the ball will arrive in his court, and weighed the alternatives for the best return. Most new sense data are already redundant (old news) by the time they reach his cortex. If really unexpected, they may perhaps cause some reflexive midcourse corrections on already anticipated actions.
A short reply also to Susan Greenfield's May 10 posting. I agree with her doubts concerning the sufficiency of the 40 hz periodicities in explaining consciousness. Not only do rats and cats show the same rhythms, but my group has found them also in curarized and anesthetized frogs (Stiles et al., Experimental Neurology 88, 176-197, 1985). At any rate, whether we ascribe consciousness to temporal or spatial activity patterns, we would still need a homunculus to observe the mess.
We are caught again in the computer metaphor , where a final, or output state, is read and interpreted by an intelligence outside the machine. In my sketchpad model (Consciousness and Cognition 4, 346- 368, 1995; also MIT Press proceedings of Tucson I) there is no final state. The dynamics I envision are iterative and self-referent. I disagree with Susan who claims that the "mere feedback" makes for "too static" a model. The top-down control of mental imagery is no mere feedback. On the contrary, the mental images that, we know, take place rather peripherally in the sensory system, are culled from the massively parallel activities in the prefrontal cortex, the presumed 'working memory'. There, past, present and future are mixed as I pointed out above. Many simultaneous associations are brought up, together with the personal genetic ideosynchracies that Jung has called "our two-million-year-old self". The selection, which I proposed is a hill-climbing process mediated via the brainstem, on the other hand, is a rather primitive neural mechanism.
Erich Harth
erich_harth@prodigy.com
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