Newsgroups: bit.listserv.csg-l
Date:         Thu, 8 Oct 1992 12:29:52 EDT
From:         "Bruce E. Nevin" <bnevin@CCB.BBN.COM>
Subject:      blindsight

[From: Bruce Nevin (Thu 92108 11:48:28)]

(Bill Powers (921008) ) --
> Bruce Nevin (921007) --

> Blindsight seems a little easier to understand in terms of levels of
> perception. Do things perceived this way always exist as low-level
> perceptions? That is, would one ever blindly perceive a relationship
> as opposed to an object?

Difficult to determine.  The article quotes the reports of persons with
removed or damaged visual cortices and describes the ability of these
people and of similarly lacking monkeys to discriminate visual stimuli
that (in the case of humans at least) they cannot consciously see.  A
flashed light "feels" like a billiard cue advancing or receding.  They
can discriminate the "texture" perception we have discussed (e.g. gray
target vs. B/W grating of equal brightness with lines separated by 3' of
arc).  Perhaps configurations: for example, one "guessed" at an X vs an
O on the basis of "feeling" the "smoothness" of an O or the "jaggedness"
of an X; black felt distant, white close; a square was felt as a "sharp
movement" or a "corner-shaped wave"; a triangle as "thin waves" and a
triangle with rounded sides as "thicker and quicker waves".

A plausible interpretation (which had occurred to me also) is that they
are becoming aware of signals that in normal vision are input to
configuration detectors, etc., in the cortex, and that normally are
ignored, that is, never or rarely come to awareness, because they are
after all controlled by those higher-level systems whose outputs in turn
are the signals of interest for attention.

The discussion of a sudden regaining vision in adults after some years
of training suggests that through reorganization replacements for the
missing higher-level systems were developed.  An 11-year-old child had
virtually normal vision immediately after removal of the occipital lobe
(in 1935) because of a prenatal cyst; perhaps the cyst had interfered
with vision and he had already been developing parallel systems to get
around the problem.  (Aside: does it not seem likely that I/O
requirements of neighboring higher- and lower-level systems provide a
kind of "template" for reorganization to match in creating a new system?
Well, I guess obviously: error is not reduced until those neighboring
systems are happy.  Error at level n+1 and at level n-1 results through
reorganization, eventually, in the creation of an ECS at level n.
Loss of plasticity due not to running out of neural matter, but rather
to having a larger number of possibilities for modification to exhaust
on level n+1 and level n-1 before reorg effects reach as far as level n.)

Weiskrantz was recently named a William James Fellow by the APS for his
"discovery" of blindsight, inter alia.  (I put "discovery" in quotes
with thought of his brief review of predecessors who described it but
were ignored because it was obviously impossible to see without having a
visual cortex.  Getting a notion accepted is evidently as prizeworthy as
discovery.  So persevere, Rick, you might get a Nobel yet!)

	Bruce
	bn@bbn.com
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