View Full Version : Self-Motion Perception: BBS Call for Commentators

02-26-1993, 05:19 AM
Below is the abstract of a forthcoming target article by Alexander
Werheim on motion perception and self motion that has been accepted
for publication in Behavioral and Brain Sciences (BBS), an
international, interdisciplinary journal providing Open Peer Commentary
on important and controversial current research in the biobehavioral
and cognitive sciences. Commentators must be current BBS Associates or
nominated by a current BBS Associate. To be considered as a commentator
for this article, to suggest other appropriate commentators, or for
information about how to become a BBS Associate, please send email to:

harnad@clarity.princeton.edu or harnad@pucc.bitnet or write to:
BBS, 20 Nassau Street, #240, Princeton NJ 08542 [tel: 609-921-7771]

To help us put together a balanced list of commentators, please give some
indication of the aspects of the topic on which you would bring your
areas of expertise to bear if you were selected as a commentator. An
electronic draft of the full text is available for inspection by anonymous
ftp according to the instructions that follow after the abstract.
__________________________________________________ __________________

The Direct versus Inferential controversy revisited

Alexander H. Wertheim
TNO Institute for Perception
P.O.Box 23
3769 ZG
The Netherlands

ABSTRACT: According to the traditional inferential theory of
perception, percepts of object motion or stationarity stem from an
evaluation of afferent retinal signals (which encode image motion) with
the help of extraretinal signals (which encode eye movements). Direct
perception theory, on the other hand, assumes that the percepts derive
from retinally conveyed information only. Neither view is compatible
with a special perceptual phenomenon which occurs during visually
induced sensations of ego-motion (vection). A modified version of
inferential theory yields a model in which the concept of an
extraretinal signal is replaced by that of a reference signal.
Reference signals do not encode how the eyes move in their orbits, but
how they move in space. Hence reference signals are produced not only
during eye movements but also during ego-motion, (i.e., in response to
vestibular stimulation and to retinal image flow, which may induce
vection). The present theory describes how self-motion and object
motion percepts interface. Empirical tests (using an experimental
paradigm that allows quantitative measurement of the magnitude and gain
of reference signals and the size of the Just Noticeable Difference
(JND) between retinal and reference signals) reveal that the
distinction between direct and inferential theories largely depends
on: (1) a mistaken belief that perceptual veridicality is evidence
that extraretinal information is not involved, and (2) a failure to
distinguish between (the perception of) absolute object motion in space
and relative motion of objects with respect to each other. The new
model corrects these errors, thus providing a new, unified framework
for interpretating many phenomena in the field of motion perception.

KEYWORDS: motion perception, velocity perception, self-motion,
extraretinal signal, efference copy, direct perception,
visual-vestibular interactions.

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