88 Foundations of Visual Perception
nature and effects of these cognitive operations may be prof-
itably studied in any setting that activates them. It is neither
necessary nor desirable to reinstate the typical conditions of
ordinary seeing.
Cognitive constructivism has a venerable tradition. Traces
may be found in Kepler’s (1604/2000) writings and in vigor-
ous criticism of the approach in Berkeley’s Essay Towards a
New Theory of Vision(1709/2000). Among nineteenth cen-
tury writers, cognitive constructivism is famously associated
with Helmholtz’s (1866/2000) doctrine of unconscious in-
ference as expressed, for example, in his Treatise on Physio-
logical Optics.In the twentieth century, variants of cognitive
constructivism have held center stage. The transactionalists
(Ittelson, 1960; Kilpatrick, 1950) Gregory (1970, 1997) and
Rock (1983, 1997) are prominent proponents. Current devel-
opments of the transactionalist approach are exemplified by
the view of perception as Bayesian inference (Hoffman,
1998; Knill & Richards, 1996).
Gestalt Theory
Gestalt theory proposes that the process of perception is an
executive-free expression of the global properties of the
brain. The organization and orderliness of the perceptual
world is an emergent property of the brain as a dynamical
system. Gestalt theory intends to distance itself from any
position that posits an executive (a homuncular agency) that
oversees the work of the perceptual system. The Gestalt the-
ory thus recognizes regulation but will not allow a regulator.
A dynamical system which instantiates a massively parallel
self-organizing process satisfies is regulated but does not
have a regulator. As such, the perceptual world is different
from the sum of its parts and cannot be understood by an
analytic investigative strategy that adopts a purely local
focus. To understand perception we need to discover the
principles that govern global perception. The most familiar
application of this notion involves the Gestalt principles of
grouping that govern perceived form (see chapter by Palmer
in this volume).
Gestalt theory emerged in the early decades of the century
in the writings of Wertheimer (1912), Köhler (1929, 1940),
and Koffka (1935). Although Gestalt theory fell from favor
after that period, its influence on modern thought is consid-
erable. Moreover, although ardent advocacy of the original
Gestalt theory may have come to an end with the death of
Köhler in 1967, a new appreciation for and extension of
Gestalt theory or metatheory (Epstein, 1988) has developed
among contemporary students (e.g., Kubovy & Gepshtein, in
press).
Ecological RealismThe ecological approach has also been called the theory of
direct perception: The process of perception is nothing more
than the unmediated detection of information. According to
this approach, if we describe the environment and stimulation
at the appropriate level, we will find that stimulation is
unambiguous. In other words, stimulation carries all the in-
formation needed for perception. The appropriate level of de-
scription can be discovered by understanding the successful
behavior of the whole organism in its ecological niche.
This approach appeared in embryonic form in 1950 in
Gibson’s Perception of the Visual Worldand in mature form
in Gibson’s last book (1979), in which he explicitly denied
the fundamental premises of his rivals. Despite this, a signif-
icant segment of the contemporary scientific community is
sympathetic to his views (Bruce, Green, & Georgeson, 1996;
Nakayama, 1994).Computational ConstructivismAccording to computational constructivism, the perceptual
process consists of a fixed sequence of separable processing
stages. The initial stage operates on the retinal image to gen-
erate a symbolic recoding of the image. Subsequent stages
transform the earlier outputs so that when the full sequence
has been executed the result is an environment-centered
description. Computational constructivism bears a family
resemblance to cognitive constructivism. Nevertheless, the
computationalist is distinguished in at least three respects:
(a) The canonical computationalist approach resists notions
of cognitive operations in modeling perception, preferring to
emphasize the contributions of biologically grounded mech-
anisms; (b) the computationalist approach involves stored
knowledge only in the last stage of processing; (c) the com-
putationalist aspires to a degree of explicitness in modeling
the operations at each stage sufficient to support computer
implementation.
Computational constructivism is the most recent entry
into the field. The modern origins of computational construc-
tivism are to be found in the efforts of computer scientists
to implement machine vision (see Barrow & Tenenbaum,
1986). The first mature theoretical exercise in computational
constructivism appeared in 1982 in Marr’s Vision.
The preceding may create the impression that the vision
community can be neatly segregated into four camps. In fact,
many students of perception would resist such compartmen-
talization, holding a pragmatic or eclectic stance. In the view
of the eclectic theorists, the visual system exploits a variety