What is
this picture? As you search for meaning in this picture your brain
strives to make sense of the seemingly meaningless spots. If,
after a good effort, you still see no meaning in the picture read the answer
below. Once you "see" the solution it
will never again be meaningless to you.
So What's Going On?
This experiment shows that
past experience can affect your perception of such properties as form or
depth. Consider what happens when you view this illustration. At first
most people cannot tell what this picture depicts, but with continued inspection
or a hint, the fragments suddenly are perceptually reorganized and recognized,
in this case, as a Dalmatian dog. A recognizable image emerges that had
no perceptual reality before. Hence, there is some sort of perceptual change
among the neurons in your brain. This also leads to a change in the
way in which you perceive the shape and depth of the scene. Perhaps most
importantly, the figure now looks like the object it was supposed to represent
- it now has the shape and depth relations of a Dalmatian dog.
Sometimes being told that a
Dalmatian hides in this scene can provide the visual system with enough
of a hint to recognize the dog. This is a case in which a high-level brain
area underlying language comprehension tells a lower-level area, in this
case the cortical areas dedicated to visual scene analysis, what might
be going on.
If this dog was animated then
it would be immediately apparent. Common motion of a group of otherwise
unrecognizable blobs is a very powerful cue for your visual system. It
enables your visual system to realize that it's dealing with a single object.
This effect is termed grouping. It is important that an animal can do this
well, otherwise it might not easily spot a predator, prey or other
food, such as apples. Animals must be able to separate the figure from
the ground. What we call camouflage is an attempt to deceive these processes.
A stalking cat moves cautiously and freezes from time to time to avoid
giving motion clues to its prey. It has even been suggested that our good
color vision evolved to enable our primate ancestors to spot colored fruit
against a confusing background of green leaves. What gives us so much visual
pleasure may originate as a device to spot our food and to break camouflage.
In most illustrations,
we tend to perceive a figure that stands out from the background. In printed
material, the figure is usually darker than its background. Figures
also tend to be smaller and more regular than backgrounds. Sometimes these
principles do not hold, and we have difficulty distinguishing figures from
their backgrounds. However, this difficulty disappears when our brain somehow
organizes these difficult visual images into a meaningful and recognizable
pattern. When this is done, only the figure and background can be seen,
and whatever was seen before is gone forever! Once you understand
what is being presented, your perception changes, and you will be fixed
on the "correct" interpretation forever.
Since these types of
figure/ground figures do not lead to immediate identification, the mental
recognition of the "correct" figure must be perceptual in character.
After all, the image does not change on your retina. Thus we can assume
that some mental process that precedes or accompanies the moment of recognition
entails a perceptual reorganization.
Second Experiment.
Now that you have recognized
the Dalmatian dog, try perceiving the image in its original meaningless
way. You will find it almost impossible to do.
Once you have recognized
the Dalmatian dog, it becomes almost impossible to see the picture in its
original meaningless interpretation. The picture becomes permanently
meaningful. This is in contrast to a truly bistable or ambiguous
figure that has two equally likely interpretations. The bistable or ambiguous
figure will "flip" between two states perennially, because your brain cannot
decide which one is more meaningfully biased over the other one.
In the case of
the Dalmatian dog, however, once your brain perceives the "correct" image
and ascribes meaning to the picture, your brain will not be able to perceive
a meaningless image again, because the meaningless interpretation is no
longer equally biased with that of your past experience with Dalmatian
dogs.
During all the
time you were staring at the picture, the image on your retina did not
change. Rather, your brain worked to construct a correct interpretation
of the image, trying out different interpretations, until your brain "recognized"
something. This emphasizes that perception is an active process of
constructing a scene description.
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