From newshub.ccs.yorku.ca!ists!torn!utcsri!rpi!usc!cs.utexas.edu!uunet!trwacs!erwin Thu Jul  9 16:19:29 EDT 1992
Article 6349 of comp.ai.philosophy:
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>From: erwin@trwacs.fp.trw.com (Harry Erwin)
Newsgroups: comp.ai.philosophy,comp.ai.neural-nets
Subject: Holographic Memory
Message-ID: <646@trwacs.fp.trw.com>
Date: 23 Jun 92 12:40:09 GMT
Followup-To: comp.ai.philosophy
Organization: TRW Systems Division, Fairfax VA
Lines: 37

I've been looking at the theory of holography and the standard model of
the cerebellum and it appears that there is a consistent holographic
interpretation of the standard model of the cerebellum that avoids the
apparatus that Karl Pribram imports into his holonomic theory. I've even
been able to identify the reference and signal beams.

To understand this, consider a zone plate, the simplest of holograms. It
focuses a coherent monochromatic beam to a point by modulating the amount
of light transmitted as a function of the desired phase at the focus. The
more out of phase the light, the more it is suppressed. Thus the reference
beam is converted into a signal beam by inhibiting the undesired
components. In the cerebellum, the individual Purkinje cell operates in
the same fashion: if the mossy fibres indicate that the body is in this
position, if you see a specific pattern of pyramidal cell activations, if
the olivary nucleus indicates that the learned motor pattern you are
associated with is activated, then inhibit a specific pyramidal cell (and
hence a specific motor action). The reference beam is the crude set of
pyramidal cell activations; the signal beam is the set of activations
after modulation by the Purkinje cells to eliminate undesired motor
neuron activations.

This model has the properties desired: memory is distributed; the effect
of ablation is not to eliminate a memory, but rather to "fuzz it up." The
large amount of spare capacity in the brain is explained without having to
assume such a low reliability that a high degree of redundancy is
required. Penfield's results are not contradicted, and the standard model
of the cerebellum still emerges triumphant.

An interesting question is the identity of the corresponding reference and
signal beams in sensory and conceptual memory. The mechanism is likely to
be similar, but I don't doubt that the details differ.


-- 
Harry Erwin
Internet: erwin@trwacs.fp.trw.com



