Illusion - Is Seeing Really Believing?/Illusion - Is Seeing Really Believing (1998)(Marshall Media)[Mac-PC].iso/pc/illusion/rock_txt.cxt/00234_Text_ref22t.txt

Text File | 1997-02-04 | 2KB | 57 lines

    Other things being equal, we
also tend to group together
units that are similar to one
another. Similarity can be of
color, of lightness, or of size.
The similarity of the shapes of
the units to one another is
more problematic. Apparently,
small line segments of one
orientation tend to be
perceived as a group when
embedded in other line
segements of a different
orientation. However, arrays of
T-shaped units, composed of
horizontal and vertical line
segments, are not readily
perceived as a segregated array
when embedded in arrays of L-
shaped units, which are
composed of similarly oriented
segments. Differences in
orientation seem to be of great
importance in the grouping of
arrays of units, as well as in
forming boundaries segregating
otherwise similar unit arrays. A
well-known test for color
vision is based on segregation
as a function of color
similarity. If one is colorblind,
a grouping by color similarity
will not occur. In experiments
using this technique, it has
been found that similarity of
line orientation of the units or
of parts of the units will lead to
segregation, but that,
generally, similarity of form
where line orientation remains
the same will not lead to
segregation.

    Similarity is a principle that
is clearly important in
camouflage, such as in
countershading in fish. A fish
is typically dark on its dorsal
surface so that, when viewed
from above, it blends with the
dark appearance of water
below; when viewed from
below, its light ventral surface
blends with the light color of
the waterΓÇÖs surface and the sky
above.