Shomari Haynes
An explanation for the consequence known as the Ponzo Effect can
be given considering
concepts associated with the Gestalt theory of perception.
Firstly, consider that in order for an object to
be perceived visually, a figure and background distinction must
be established and secondly, the gestalt
principle of proximity that objects seen closer together will be
seen as going together. With this in mind,
the two central red lines (figure), imposed on different
backgrounds, are being seen in contexts that are
different since the bottom line makes an image with
significantly more white space around it(the
bottom half of the illusion). The line at the top has less white
space on either side and is bordered
closely by the black lines; at this point in the image, the
lines are converging and the length of the line at
the top is given more significance because of its juxtaposition
to other lines of a different orientation.
When the two lines tending to vertical are removed, the red
lines appear to have the same
length. If the two black lines are set perpendicular to the red
lines, again the red lines appear to be of
the same length. These basic tests I think demonstrate that it
is not only the presence but the
orientation of the vertical lines which cause the Ponzo Effect.
The presence of the two black lines, alter
the background upon which the red lines appear, in essence
altering the images creating two different
groupings or gestalts.
Taking the framework for empirical tests from lecture 6 on the
perception of object size, the
frequency of occurrence of lines being the same length in the
presented between two non-parallel,
convergent lines can be measured where one should expect to see
that the effect presented in the
illusion is hardly found in nature or probabilistically low. In
other words, it more likely that in the real
world the top line will really be longer than the bottom line
when the 4 lines have that orientation.
Again, the significance of each red line is changed in relation
to its surroundings (background) by
the orientation of the black lines converging to the top of the
figure. The top line is thought to be longer
and thus seen as longer. With knowledge of the effect, and
practice, the two lines can even be seen as
the same length since the effect is only improbable and not
impossible as other optical illusions are.
One impact of this empirical approach is it provides the basis
for a developmental theory of
vision where after enough experience has been accumulated, the
visual system then works on given
perceptual rules of thumb to render a representation or
interpretation of the environment. It
demonstrates not only that the physical eye has evolved, but the
process of perception itself has
evolved since visual perception can be predicted based on the
probability of given occurrences in a
context. These rules may be the building blocks of what become
the phenomenological invariant
properties of vision such as Gestalt principles. At the same
time it points that what is seen is not
necessarily what is explicitly out there and the real world as
the notion that it can be seen truly as it is
left to hang in doubt.
