Aspects of Perception

The Gestalt laws may play a primary
role, but learning certainly plays a secondary, and important, role.

Let‘s say that a simple melody is played
on the piano in the presence of Tina, a two-week-old infant. Assume that Tina
has had little or no experience with hearing music. Does she now actually
perceive a melody in somewhat the same way that

you perceive it? Or does she
just hear a lot of disconnected tones? You can put yourself in Tina‘s position
to some extent by imagining yourself listening to the music of another country,
one that uses a tonal scale and patterns of harmony that are unfamiliar to you.
When you first hear a song, it may seem to have little or no pattern. However,
hearing it two or three times will help you to perceive the pattern. To the
extent that you, or Tina, can hear any pattern at all on the first
presentation, it is probably due to the Gestalt laws. The sharpening of
perception on repeated presentations can be attributed to learning.

One way to explain this sharpening of
perception is to suggest that patterns of stimulation set off chain reactions
in neurons located in the association areas of the brain‘s cortex. Each time a
given stimulus is presented, the same set of neurons fire. The research of the
Canadian psychologist Donald O. Hebb suggests that repeated firings form a cell
assembly, a stable group of neurons that are used over and over by the brain to
create a representation of the external pattern. A pattern can, of course, be
quite complex. If this is so, a given cell assembly may represent only a
portion of a pattern. Hebb called a set of cell assemblies grouped together to
form a larger pattern a phase sequence.

The existence of cell assemblies helps
account for a memory of patterns and perceptual objects. When you hear a melody
or recognize something you have seen before, it is quite possibly because an
established cell assembly is firing.

Learning also plays
a role in perception because we are conscious beings who attach labels to
perceptual objects. This brings us to the cognitive hypothesis in perception,
the hypothesis that we not only perceive, but know what we are perceiving. Cognitive
learning, learning in which consciousness plays an important role, is an
important aspect of the perceptual process.

An illusion is a false perception, a
perception that does not fit an objective description of a stimulus situation.
An illusion is usually associated with a particular sense. Consequently, there
are optical illusions, auditory illusions, and so forth. Illusions tend to be
remarkably stable. They affect most normal observers in the same way. For
example, for almost all of us the Moon is perceived to be larger when low and
near the horizon than when it is high and overhead.

It is important to distinguish the
concept of an illusion from a delusion and a hallucination. A delusion is a
false belief. If Ray, a schizophrenic mental patient, believes that he has an
eye with X-ray vision on the back of his head, this is a delusion. A hallucination
is a perception created by the individual. It has no relationship to reality at
all. If Ray sees and hears an invisible companion that nobody else can see or
hear, this is a hallucination. Illusions are thought to be normal and
experienced by most of us. Delusions and hallucinations are thought to be
abnormal and experienced in an idiosyncratic fashion.