Theories and Foundational Questions 95Moderate Modularity. Moderate modularity is defined
by a list of features made explicit by Fodor (1983) in his
Modularity of Mind.To the two criteria given above, Fodor
adds several others: that modules are informationally encap-
sulated, that modular processes are unconscious, that modu-
lar processing is very fast and obligatory, that modules have
shallow outputs, that modules emerge in a characteristic on-
togenetic sequence, and that following insult modules exhibit
characteristic disruption.
Among cognitive psychologists, claims for modularity
tend to be measured against Fodor’s expanded list. Unsur-
prisingly, when the expanded list of criterial features is
adopted, agreement on modularity is harder to reach. Much
of the controversy involves encapsulation. By this test, a
dedicated biological device that is uniquely sensitive to an
eccentric form of stimulation will be considered to be a mod-
ular component only if under normal conditions of its opera-
tion its processes run their course uninfluenced by factors that
are extraneous to the module. Neither concurrent activity in
other modules nor reference to stored knowledge of past
events or anticipations of future events affects the module.
The module is an impenetrable encapsulated system (Fodor,
1983; Pylyshyn, 1984).
Two kinds of problems recur in assessments of encapsula-
tion. First, it is universally accepted that performance of al-
most any task may be affected by a host of cognitive factors.
Accordingly, the claim for encapsulation says that however
these cognitive factors influence performance, they do not do
so by influencing the computations of the module. Conse-
quently, an experimental demonstration that performance is
affected by cognitive factors or by the output of parallel com-
putations does not necessarily negate modularity unless it can
be shown that the effects are located in the computations that
are endogenous to the putative module. This latter assertion
is hard to establish (e.g., Pylyshyn, 1999).
Second, there is the problem of the practice effect. That is,
performance of a task that seems unlikely to be supported by
a dedicated biological device or to be dependent on access to
special stimulation will exhibit many of the features of mod-
ularity when the task is highly practiced. For example, per-
formance may become very fast, mandatory, and inaccessible
to conscious monitoring. Consequently, evidence that the
process underlying performance exhibits these features does
not necessarily implicate modularity.
Strong Modularity. Strong modularity adds to the com-
posite list just given the added requirement that the candidate
module exhibit a distinctive style of processing. Although no
one has advanced this claim explicitly, it is implicit in the
writings of modularists that modules work by implementing
the same process. As two examples, in Marr’s (1982) ap-
proach all the modules are noncognitive computational de-
vices, and in Fodor’s (1983) canonical analysis of modularity
all of the modules are inferential engines. Because the modu-
larity stance does not seem tied to views of process, a stance
on modularity does not exert strong constraints on the char-
acterization of the perceptual process. Thus an ecological
realist might also adopt modularity, holding that the modules
are independent devices for detection (pickup) of information
in spatiotemporal optical structure.
Although the postulation of modularity is compatible with
a variety of positions regarding perceptual process, an excep-
tion to the rule must be made for cognitive constructivism.
On the face of it, modularity and cognitive constructivism
cannot be linked except in the weak sense of modularity (the
first construal). The cognitive constructivist takes the percep-
tual process to be a cognitive process that ranges freely over
the knowledge domain. The principal arguments for the
claim that the perceptual process is a form of “hypotheses
testing” or “intelligent problem solving” very often take the
form of demonstrations that perception is cognitively pene-
trable (e.g., Rock, 1997). Certainly this is the way that the
cognitive constructivist wishes to be understood.On Illusion and VeridicalityGenerally, perception is a reliable guide to action. Occasion-
ally, however, perception misrepresents and action predicated
on the implications of perception fails. Perceptual misrepre-
sentations arise under a variety of conditions: (a) The normal
link between the environmental state of affairs and optical
input is severed: For example, the spatial arrangement of
points on the retina and the spatial arrangement of points
comprising an environmental object are normally in align-
ment. A straight stick will have a correspondingly straight
retinal contour associated with it. However, if the stick is half
immersed in water, the different refractive indices of water
and air will result in a “bent” retinal contour. Under these
circumstances the straight stick will look bent. (b) The nor-
mal pattern of neuronal activation engendered by exposure to
a distal arrangement is modified: For example, continuous
visual inspection of a line tilted in the frontal plane will mod-
ify the pattern of activity of neuronal orientation detectors.
The resultant perceptual effect is an alteration of perceived
orientation; a test line tilted in the same direction as the in-
spection line will look upright, and an upright line will look
tilted in the direction opposite to the tilt of the inspection line.
(c) Rules of perceptual inference are overgeneralized; that
is, the rules are applied under conditions for which they are
inappropriate. A widely held view (e.g., Gregory, 1970, 1997)