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From: ln63szf@sdcc3.ucsd.EDU (Rick Frey)
Newsgroups: net.ai,net.philosophy,net.cog-eng
Subject: Re: Gibson's theory of perception
Message-ID: <3487@sdcc3.ucsd.EDU>
Date: Wed, 23-Jul-86 15:34:23 EDT
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Posted: Wed Jul 23 15:34:23 1986
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> Visual perception and interpretation is of course based on light striking
> the retina.  However, reflected light from from an object is not really
> the only way to perceive objects.
 
> The best example of this is the filling in process that takes place to
> prevent our "perceiving" the blind spot of each eye.  

At first I thought this sounded ok, but then I found a somewhat
significant nit I could pick, so...

You're correct that things can be perceived that are not present as
stimulation on the retina, but, especially in the example you give, the
'filling in' that takes place is driven by hard-wiring in the neural
system that *knows* about this whole in the visual field.  Thus, the
perceptual information still does not come from the object itself, but
from the machinery that knows about the properties of objects.

As a criticism in favor of Gibson, this doesn't work.  As a statement
that there is more to perception than the retinal image, agreed.

> Another example is my original dissertation topic: subjective contours.
> Artists have long known that you can "suggest" contours and edges by
> manipulating the placement of black areas.  There are ways to place
> lines and black areas to force the visual system to perceive whole
> and sometimes complex objects (curved, etc.)  

Another good example of the perceptual system going beyond the retinal
image (or Gibson's "ambient array of light") in order to 'make sense' 
out of the perceptual information.  

> Another example of perceiving objects without the need of the object's
> reflected light falling on the retina is visual hallucinations.  High
> fever, sensory deprivation, psychoactive drugs, etc. all can cause this
> experience.

Many psychologists wouldn't call these 'true perceptions' because their
source isn't the perceptual system.  It's kind of an odd thought to say
that in a dream, you aren't *really* seeing anything, but in many senses
(bad pun, I know) you aren't.

			Rick Frey
			(...ihnp4!sdcsvax!sdcc3!ln63szf)
			(ln63szf%sdcc3@sdcsvax.UCSD.EDU or .ARPA)