Illusion - Is Seeing Really Believing?/Illusion - Is Seeing Really Believing (1998)(Marshall Media)[Mac-PC].iso/pc/illusion/rock_txt.cxt/00097_Text_res06t.txt

Text File | 1997-02-04 | 2KB | 52 lines

Failure of Constancy

In many instances in daily life,
objects located at very great
distances appear extremely
small. Consider, for example,
the striking smallness of
houses viewed from a plane
traveling at an altitude of
20,000 feet or the size of people
on the street when viewed from
a skyscraper. Students of
perception have used such
expressions as "the falling off
of constancy" and
"underconstancy" in
describing these instances.

    The logic behind this
terminology is straightforward.
Constancy can be no better
than the sensory information
on which it is based. Because
our sensory capacities are
limited, we are not always able
to achieve full constancy. With
respect to size constancy, for
example, one might say that
the maximum distance that can
be detected perceptually is on
the order of hundreds or, at
most, thousands of yards. We
can thus hardly expect that the
distance to, say, the moon,
which is 250,000 miles away,
will be perceived accurately.
Instead we should expect the
moon over the horizon to
appear to be about the size of a
house or other terrestrial
object of the same visual angle
on the horizon. Since the moon
is roughly 2000 miles in
diameter, one might say that we
have here a considerable
departure from constancy. But
it is important to note that the
failure does not lie with the
perceptual apparatus
responsible for constancy but
with the information available
to it.