In the heyday of the
Behaviorist movement in
psychology, it was argued that
perception is not a proper
subject for scientific
investigation because
perceptions are subjective
states. In other disciplines of
science, it was said, the facts
are open to public observation,
whereas the contents of mind
are not in themselves directly
observable.

    It is true that no one else
can look at my perception of an
object. Suppose I experience
the illusion that vertical lines
in an illustration are curved,
although they are in fact
straight. If I report that the
lines seem curved, no one can
confirm that I have seen what I
report. But others can confirm
the perceptual phenomenon for
themselves, and they can also
report on their own perception
of the lines. Thus, while we
cannot observe peoples'
perceptions per se, we can
confirm or disconfirm their
generality and infer whether or
not they actually occur. In
philosopher John Searle's
words, perception, like other
kinds of mental states, has a
"first person ontology": its
reality is subjective, but that
doesn't make it any less real or
entitle us to cast it aside as a
subject unsuitable for
scientific investigation,
particularly in light of the fact
that conscious and non-
conscious mental events are
caused by brain events.