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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: <3483@sdcc3.ucsd.EDU>
Date: Sun, 20-Jul-86 17:22:30 EDT
Article-I.D.: sdcc3.3483
Posted: Sun Jul 20 17:22:30 1986
Date-Received: Mon, 21-Jul-86 23:42:10 EDT
References: <1782@mtuxo.UUCP>
Organization: U.C. San Diego, Academic Computer Center
Lines: 123
Summary: What a topic!
Xref: mnetor net.ai:1055 net.philosophy:2184 net.cog-eng:234

I haven't read Kelley's book either, but I'm pretty familiar with Gibson
and a few of the major problems in his theory, most of which you
present.

In article <1782@mtuxo.UUCP>, hfavr@mtuxo.UUCP (a.reed) writes:
> In the
> standard contemporary conceptualization of perception, from which Gibson
> dissented, the input to the perceptual process is thought to be the
> sensory impression; for example, in visual perception, the pattern of
> retinal stimulation. 

Here you start off a bit unclear.  When you talk about input to the
perceptual process, to what are you referring?  The signals that will
travel down the optic nerve?  What will end up in the occipital cortex?
Area 17?  You need to be more specific, as did Gibson.

> If the perceptual system is
> thought of as physically limited to the eye and the brain, the standard
> view is close to being a logical necessity. It is from this
> conceptualization that Gibson dissented.

A distinction that most physiological psychologists won't make.  All
(all good) PS's know that at some point, information about the
regularities of the external world need to be used in order to make
sense out of visual stimuli.  Helmholz, Rock and some others say that
this information comes in the form of conscious structuring of visual
information whereas Ramachandran and some others say that the
regularities of the external world are hard wired into the perceptual
features of the system.  Thus the Phi phenomenon (illusory motion) isn't
do to a conscious realization that objects blinking between two
locations might be moving between them, it's do to a hardwired
understanding that in the real world, objects have to travel through
paths to get to another location; blinking is impossible.

> In Gibson's view, the perceptual system is not limited to the confines
> of the organism, but extends into the environment. In the course of its
> evolution, the organism has assimilated physical mechanisms present in
> its natural environment to function as integral parts of its perceptual
> system. 

This isn't only Gibson's idea.  I'm not sure on who came up with it
first, but he certainly isn't the sole posessor of the idea.

> In this view, the
> natural light sources present in the environment, the reflective
> properties of the surfaces of objects, and the optical characteristics
> of the atmosphere are as much a part of the human perceptual system as
> the eyes and the brain. Thus, the retinal stimulation pattern is not the
> input to perception, but rather an internal stage in the process. The
> input to the perceptual process is the object itself; 

Gibson's major mistake.  This simply isn't true.  Obviously it has to be
the light that makes it to the organism.  If no light reaches the
organism, then there's no perception.  Period.  Unless the organism
*perceives* the object, it doesn't exist to the perceiver.  Perception
starts once there is something to perceive, and that only can begin when
perceptual information about the object makes its way to the perceiver.

> the output is
> organism's awareness of the object. The information contained in this
> awareness is the original, and not a re- (or transformed), presentation
> of the object to consciousness.

Information contained in awareness?  This is somewhat Gibsonian in that
he uses words that have no clear definitions, but I don't think even he
would quite say this.  What is awareness?  What stage of processing are
you referring to?  Aside from the actual collection of excited and 
inhibited receptors at the retinal level, *all* perception is transfor-
mation.  Sorry, no homunculae.  (sp??)

> According to Gibson, the experimental psychologist's laboratory use of
> two-dimensional representations, tachistoscopic stimuli, illusions, and
> other materials that were not part of the ecological environment in
> which the human perceptual system evolved, amounts to studying the human
> perceptual system with some of its key parts removed. 

In some cases, this is a valid claim of Gibson's, but his whole theory
rests on it and it isn't 100% true.  He'd love to have us believe that
the external world is rich in information and that perception is an easy
task of picking out of the multitude of cues available.  That's simply
not true.

Experimental psychologists aren't blind to this criticism, and far too
many experiments have been done that don't fall under Gibson's
criticisms of artificiality.  Perception developed under situations
where the available information was far from over-abundant.  Without
this over-abundance of information, Gibson's ideas start falling apart.

> This is rather like trying to find out how a computer works after 
> pulling out some of its chips, 

This is a purely Gibsonian analogy, and accordigly isn't accurate.
Studying perception in the laboratory removes nothing from the
perceptual machiney.  It removes perceptual information that Gibson
says has to be there, which, I'm sorry, but you don't get to tell nature
"Make sure all the information I need is there or I'm going to screw
up."  Adaptivity would seem to indicate that an organism that could
still make the best judgement with the least information would be the
most fit to survive.  Perception developed in a piecemeal fashion such
that there wasn't an overabundance of information at various stages in
the development.  So where did this 'perceptual laziness' come into
play?  You try finding a small tree frog in a huge tree.  The whole idea
of an overabundance of perceptual information might apply to recognizing
people's faces, but it has no basis in the reality of where and how
perception developed.

> To yield valid information, the results of
> such experiments must be interpreted with special attention to the fact
> that one is not studying an intact or properly functioning system.

True, but with the modified analogy, if you put a number into the
computer and get something out, if the machinery is the same in all
states (which in reality, it is) you get information any time you put
something in and get something out.  Don't throw it away because it
isn't an exact analogy to the natural environment.  You do need to be
careful in interpretting what you find, but the answer isn't to say that
is's all artificial and the only real perception stems from objects in
the natural world.

			Rick Frey
			(...ihnp4!sdcsvax!sdcc3!ln63szf)
			(ln63szf%sdcc3@sdcsvax.UCSD.EDU or .ARPA)
			(I've been switched temporarily to sdcc3, NOT sdcc7)