BARNARD@SRI-STRIPE.ARPA.UUCP (07/14/86)
Maybe I've never really understood the arguments of the so-called "perceptual realists" (Gibson, etc.), because their position that we do not build internal representations of the objects of perception, but rather perceive the world directly (whatever that means), seems obviously wrong. Consider what happens when we look at a realistic painting. We can, at one level, see it as a painting, or we can see it as a scene with no objective existence whatsoever. How could this perception possibly be interpreted as anything but an internal representation? In many or perhaps even all situations, the stimuli available to our sense organs are insufficient to specify unique external objects. The job of perception, as opposed to mere sensation, is to complement the stimulus information to create a fleshed-out interpretation that is consistent both with the stimulus and with our knowledge and expectations. Gibson emphasized the richness of the visual stimulus, arguing that much more information was available from it than was generally realized. But to go from this observation to the conclusion that the stimulus is in all cases sufficient for perception is clearly not justified. -------
theo@ARI-HQ1.ARPA ("FENG, THEO-DRIC") (10/03/86)
I just ran across the following report and thought it might contribute some-
thing to the discussion on the "perception" of reality. (I'll try to summarize
the report where I can.)
according to
Thomas Saum in the
German Research Service,
Special Press Reports,
Vol. II, No. 7/86
A group of biologists in Bremen University has been furthering the theory devel-
oped by Maturana and Varela (both from Chile) in the late '70's, that the brain
neither reflects nor reproduces reality. They suggest that the brain creates its
own reality.
Gerhard Roth, a prof. of behavioral physiology at Bremen (with doctorates in
philosophy and biology), has written several essays on the subject. In one, he
...writes that in the past the "aesthesio-psychological perspective"
of the psychomatic problem was commonly held by both laypersons
and scientists. This train of thought claims that the sensory organs
reporduce the world at least partially and convey this image to the
brain, where it is then reassembled ("reconstructed") in a uniform
concept. In other words, this theory maintains that the sense organs
are the brain's gateway to the world.
In order to illustrate clearly the incorrectness of this view,
Roth suggests that the perspectives be exchanged: if one looks at
the problem of perception from the brain's angle, instead of the
sense organs, the brain merely receives uniform and basically homo-
geneous bioelectric signals from the nerve tracks. It is capable of
determining the intensity of the sensory agitation by the frequency
of these signals, but this is all it can do. The signals provide no
information on the quality of the stimulation, for instance, on whe-
ther an object is red or green. Indeed, they do not even say any-
thing about the modality of the stimulus, i.e. whether it is an
optical, acoustical, or chemical stimulation.
The constructivists [as these new theoreticians are labeled],
believe that the brain is a self-contained system. Its only access
to the world consists of the uniform code of the nerve signals which
have nothing in common with the original stimuli. Since the brain
has no original image, it cannot possibly "reporduce" reality; it
has to create it itself. "It (the brain) has to reconstruct the di-
versity of the outside owrld from the uniform language of the neu-
rons", Roth claims. The brain accomplishses this task by "interpret-
ing itself", i.e. by construing what is going on inside itself.
Thus, the brain "draws conclusions" from the degree to which it is
agitated by the modality of the original stimulus: all neuronal im-
pulses reaching the occipital cortex, for example, are visual im-
pressions.
This isolated nature of the brain and its reality, however, are
by no means a blunder on the part of nature; indeed, they are not
even a necessary evil, Roth explains. On the contrary, it is an
adaptive advantage acquired by more highlly developed creatures dur-
ing the course of their phylogenic development. If the brain had di-
rect access to the environment, Roth argues, then one and the same
stimulus would necessarily always result in one and the same reac-
tion by the organizsm. Since, however, the human brain has retained
a certain amount of creative scope for its reconstruction of reality,
it is in a position to master complicated stiuations and adapt itself
to unforeseen circumstances.
Only in this way is it possible to recognize an object in differ-
ent light intensities, from a new angle of vision, or at a distance.
Even experiments with "reversal spectacles" demonstrate man's powers
of adaptation in interpreting reality: after a little while, test
persons, who see the world upside down with special glasses, simply
turn their environment around again in their "mind". When, after a
few days, they remove the spectacles, the "real" world suddenly seems
to be standing on its head.
This mobility and adaptability on the part of our perceptive fa-
culties were obviously much more important for the evolution of more
highly developed vertebrates than was a further intensification of
the signal input by the sense organs. The million fibers in man's
optic nerve are only double the number of a frog's; the human brain,
on the other hand, has one hundred thousand times more nerve cells
than a frog brain. But first and foremost, the "reality workshop",
i.e., the cerebral area not tied to specific sense, has expanded
during the evolution of man's brain, apparently to the benefit of
our species.
Contact: Prof. Dr. Gerhard Roth, Forschungsschwerpunkt Biosystemforschung,
Universitat [note: umlaut the 'a'] Bremen, Postfach 330 440,
D-2800 Bremen 33, West Germany.
[conveyed by Theo@ARI
------