Gareth Evans (1982)
argues that perception is belief-independent and in order to substantiate this
claim he cites the well known example of the Müller-Lyer optical
illusion. He points out that despite any justified beliefs we may have about
the actual lengths of the lines: "[i]t will continue to appear to us
as though, say, one line is longer than the other even when we are quite sure
that it is not." Kelly (1998) endorses Evan's anti-intellectualist view
that beliefs have no impact on our perceptions:
"Because perceptions are not subject to the
canonical norms of rationality, then - because they are not, in other words,
"rationally revisable" - they do not stand within the web of
inferential relations that constitutes our beliefs, and ought not to be explained
in terms of them."
For Kelly this web of
inferential relations enables us to form beliefs, to make judgements and to
infer conclusions. Despite the fact that there is no evidence to challenge this conclusion, it remains a commonplace amongst philosophers to talk of
"perceptual judgements" as if they are independent of
"canonical norms of rationality." Evans is clear on this point. For
him, judgement is connected with reasons and reasons are conceptual. If we
are to avoid explaining perception by reference to "inferential
relations" and "canonical norms of rationality" —of reasons—
then something less extravagant than judgement is required.
We already have a
candidate in Brook's theory of perception as a capacity to represent the
things with which the perceiver is engaged. In order to explore this
conjecture it will be helpful to examine some frequently overlooked but
nonetheless revealing anthropological research.
In one of the largest
studies of its kind, Segal et al (1966) oversaw a global survey of cross
cultural variations in susceptibility to optical illusions. The researchers
found significant variance between differing communities and age groups. For
example, some groups reported no difference between the lengths of the lines of
the Müller-Lyer diagram. An earlier study by Hudson (1960), of culturally
isolated South African children, encountered very similar findings. Both
studies attributed the results to a lack of habitual exposure to pictures
amongst the communities studied, and Hudson dubbed this: "pictorial
illiteracy." In fact, even children well schooled in language and
arithmetic skills (but lacking pictorial literacy) were not susceptible to what
is commonly described as the "pictorial illusion of depth" and were
therefore unsusceptible to the simulated spatial depth that many optical
illusions exploit.
McCauley and Henrich
(2006) write:
"For those who experience it, the illusion may
persist, but susceptibility to the Müller-Lyer illusion is neither uniform nor
universal. Moreover, a plausible argument can be made that through most of our
species’ history most human beings were probably not susceptible to the
illusion."
If this is true, and
corroborating evidence can be provided from the art historical record as well
as other sources (Deutscher 2010), then we have very good reason to suppose
that our skills in the use of depictions are significantly implicated in the
perplexities of such optical illusions. So, the conflicting responses we
have when faced with the Müller-Lyer diagram are simply explained by the fact
that we are disposed to represent the diagram in two different ways. We can
treat the lines as a simulation of spatial depth or else we can treat them as
two lines of equal length. No judgement need be imputed.
If the capacity to
derive depth-cues from perspectival images is culturally acquired and is not an
immediately available part of our genetically inherited perceptual repertoire
then we have very good reason to suppose not only that perception is belief
independent, as Evans claimed, but that perception is both non-conceptual and
non-depictive. Language and depiction are skills that have
developed through cultural evolution and both take time and practice to
acquire. The capacity to imitate the behaviour of others on the other hand—to
produce rudimentary versions of what Brook (1997) calls "Matching”
representations—is an inherited skill upon which all of our more sophisticated
communicative capacities supervene.
In Part VIII I will
explore Kelly’s claim (pace Evans) that “Perceptual content is, sometimes at
least, irreducibly articulated in terms of dispositions by the perceiver to act
upon the object being perceived.” In doing so, I aim to explain how this gives
strong support to the thesis that perception is fundamentally a communicative
capacity: “a disposition to act” in
representational terms “on [or with] the object being perceived.”
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