Illusion - Is Seeing Really Believing?/Illusion - Is Seeing Really Believing (1998)(Marshall Media)[Mac-PC].iso/mac/ILLUSION/SROCK_TX.CXT/00437_Text_re26t.txt

Text File | 1996-12-31 | 2KB | 56 lines

    Another theory reverses the
argument, in a manner of
speaking. It assumes that the
first step in processing is the
creation of the illusory figure.
The lightness effect occurs
secondarily. The stimulus
pattern, for example the one
seen earlier in Chapter 5, leads
initially to the perception of
the colored fragments as figures
on a white ground. That is what
we should expect from bottom-
up processing based on
principles of figure-ground
organization. To perceive the
white rectangular region,
figure-ground reversal is
necessary, and that does not
always occur if the observers
remain naiveΓÇöΓÇôthat is, if they
do not know about the
possibility. If reversal does
occur, it is probable that it does
so because it is cued by such
factors as the incompleteness
of the circular fragments,
suggesting that something is
occluding them, or by the
perfect alignment of the edges
of the rectangular gap across
the dividing space. Whatever
triggers the reversal, the fact is
that it entails the perception of
a white rectangle even though
no contours are visible except
at its corners. It is possible,
therefore, that the perceptual
system "invents" the extra
whiteness so as to "explain"
why one perceives contours
where none exist. Following
the suggested classification,
this is a nonmechanistic
theory, since the process
entails perceptual
reorganization based on the
detection of cues. The outcome
can be viewed as the preferred
solution to the problem of what
the stimulus pattern most
likely represents. Once the
illusory figure is perceived, it
is difficult to perceive the
pattern in any other way.