94 Foundations of Visual Perception
direct perception have been equally adamant in rejecting the
model of representational transformation. They maintain that
the model results from questionable premises. Once these are
abandoned, the apparent need for positing intervening repre-
sentational states vanishes.
Perception and Cognition
What is the relationship between perceptual processes and
cognitive processes? The answers to this question have
ranged widely over the theoretical landscape. The cognitive
constructivists consider perception to be perfused by cogni-
tion. In the view of the cognitive constructivist, the percep-
tual process isa cognitive process. The principal distinction
between perceptual processes and cognitive processes is that
in the former case mental operations are applied to the trans-
formation of representations originating in occurrent optical
input, whereas in the latter case mental operations are applied
to the transformation or representations drawn from the pre-
existing knowledge base. This attribution is clear-cut for con-
temporary constructivists, such as Rock (1983, 1997), who
characterize perception as a process of intelligent problem
solving, as it was in the classical description (Helmholtz,
1866/2000) of perception as a process of unconscious infer-
ence and in the New Look movement in North American psy-
chology (Bruner, 1957). The assumption that perception and
cognition are continuous is also commonly found in applying
standard information theory to problems of perception (e.g.,
Lindsay & Norman, 1977; Rumelhart, 1977).
The continuity claim is central to the cognitive construc-
tivist position. The claim rests on a diverse set of experimen-
tal observations that are said to imply the interpenetration of
perception and cognition. Many of the parade cases emerged
from the laboratory of Rock (1983, 1997). Despite the com-
pelling character of some of these cases, they have not been
decisive. Pylyshyn (1999) has presented a thorough airing of
the controversy. In his assessment the cases featured by the
cognitive constructivists do not support the claim of cogni-
tive penetrability of perception; “rather, they show that cer-
tain natural constraints on interpretation, concerned primarily
with optical and geometrical properties of the world, have
been compiled into the visual system” (p. 341).
The computational constructivist takes a more restrained
position. The aim of the computational approach is to advance
the explanation of perception without invoking cognitive
factors. Nevertheless, the full explanation of perception re-
quires cognitive operations. In the model of representational
transformation adopted by the computational approach, the
sequence of operations is divided into early and late vision.
The former is supposed to be free of cognitive influence. The
operations are executed by modular components of the visual
system that are cognitively impenetrable; that is, the modules
are encapsulated, sealed off from the store of general knowl-
edge. These operations of early vision perform vital work but
do not deliver a representation sufficient to sustain adaptive
behavior. A full-bodied, environment-centered representation
requires activation of stored mental models and interpretation
of the representations of early vision in this context. An ex-
emplar of this stance toward cognition and perception is
Marr’s (1982) computational theory.
The attitudes of Gestalt theory and the theory of direct
perception are opposed to the constructivist stance. Indeed,
in the case of Gestalt theory the difference is particularly
striking. Whereas the constructivist proposes that perception
has significant cognitive components, the larger program of
Gestalt theory proposes that much of cognition, such as
thinking and problem solving, is best understood as an
expression of fundamental principles of perception. The
theory of direct perception considers the entire perceptual
system to be encapsulated, and therefore uninvolved, in in-
teraction with other information-processing operations. This
position does not carry with it a rejection of influences of
past experience or learning in perception, but it does require
a different construal of the mechanism that supports these
influences.ModularityIs the visual system a general-purpose processor serving all
of the diverse perceptual needs of the organism, or is it a col-
lection of independent perceptual modules that have evolved
to compute domain-specific solutions, such as depth from
shading, shape, or motion? The answer to this question
depends on how modularity is construed. Consider three
construals that vary the conditions they impose on the postu-
lation of modularity (the terms weak, moderate,andstrong
modularityare ours).Weak Modularity. Weak modularity stipulates only
two conditions: (a) that a segregated bit of the biological
hardware be shown to be exclusively dedicated to representa-
tion of a specific environmental feature, such as solidity; and
(b) that the designated hardware be specialized for the pro-
cessing of a particular form of stimulation, such as retinal dis-
parity. Under this construal, when these two conditions are
satisfied, postulation of a stereoscopic depth module is war-
ranted. If this minimal set of features for modularity is
adopted, there probably will be little disagreement that the
visual system is modular.