One of the fascinating questions of
perception is this one:Why do we perceive a world of rounded shapes, of near
and far things, of depth instead of a flat world with one surface? A
second, related question is: How is this accomplished?
Depth perception is made possible by
various cues, signals or stimuli that provide an observer with
information. Depth perception is made possible by cues arising from binocular
vision and monocular vision.
Binocular vision is vision with two eyes.
The principal cue for depth perception associated with binocular vision is retinal
disparity. The pupils of the eyes are about three inches
apart. This gives the right eye a somewhat different view of a scene than the
one obtained with the left eye. Notice that although you sense two images, you
only perceive one. (This is another example of the difference between sensation
and perception.) This is sometimes called the zipper function of the brain, the
capacity of the visual portion of the cortex to integrate two images into a
meaningful whole. The whole image, in part because of retinal disparity,
appears to be three-dimensional.
Monocular vision is vision with one eye.
If a person is deprived of binocular vision, then he or she can still perceive
depth with the assistance of monocular cues. (Although the loss of the use of
an eye impairs depth perception, it does not destroy it completely.) Monocular
cues are available to one eye. These are the kinds of cues that give a
landscape painting depth. Although you normally look at such a painting with
both eyes open, in this case depth perception is not arising because of retinal
disparity. Close one eye and look at the painting. The perception of depth will
remain.
A first monocular cue is linear
perspective, the tendency of parallel lines to seem to converge as they
approach the horizon. Linear perspective was referred to earlier in connection
with the Moon illusion. A second monocular cue is interposition, a cue created
when one object blocks some portion of another object. If a person is standing
in front of a tree, and the tree is partly blocked, it is easy to see that the
tree is behind, not in front of, the person.
A third monocular cue is shadows.
Shadows are differences in illumination gradients. These tend to help us see
rounded surfaces as convex or concave. A fourth monocular cue is texture
gradient. A texture gradient is perceived when we can see less detail in far
away objects than those that are closer to us. Such a gradient appears
spontaneously when we look at a field strewn with rocks. A fifth monocular cue is motion
parallax, the tendency when moving forward fairly rapidly to perceive
differential speeds in objects that are passing by and in those that are being
approached. For example, in a traveling car, nearby telephone poles approach
rapidly and then flash by. Look down the road. The telephone poles seem to be approaching slowly. If you can see telephone poles
very far away, they seem to be almost stationary.
All of these monocular cues work together
to enhance depth perception. Telepathy belongs to a larger category of
phenomena called extrasensory perception. Extrasensory perception, or ESP, is
the capacity to be aware of external events without the use of one of the
conventional senses such as vision or hearing. ESP is referred to as the sixth
sense, there are at least seven readily identified senses. ESP should more
accurately be called the eighth sense.
There are three kinds of extrasensory
perception: (1) precognition, (2) telepathy, and (3) clairvoyance. Precognition
is the power to know what will happen in the future. Living almost five hundred
years ago, the French physician and astrologer Nostradamus is one of the more
famous individuals in history purported to have had precognitive powers.
Telepathy is the power to send and
receive mental messages. The ability to read the minds of people who can‘t read
yours is also considered to be a telepathic power. A spy with this ability
would have a useful psychological tool.
Clairvoyance is the power to have
visions and ―see something out of the range of normal vision. (The word clairvoyance
has French roots meaning ―clear seeing.) Some clairvoyants are asserted to be
able to give medical readings and visualize an illness in another person in the
same way that an X-ray machine can. A person who can combine the two powers of
precognition and clairvoyance is thought to be able to both predict and
visualize future events. The term seer implies an ability to combine
these powers. Although not a form of ESP, there is another power often
associated with it. This is psychokinesis or PK. Psychokinesis is the power to
move objects using only energy transmitted by the mind.
All four of the phenomena mentioned
above are combined into a general class of mental abilities called psi powers,
powers of the mind that are thought to transcend the conventional laws of
physics and our ordinary understanding of natural science. Psi powers are
sometimes also called ―wild talents.
It is not possible
at this time to make a simple statement saying that psychology either accepts
psi abilities as real or rejects them as false. It can be asserted that
many psychologists—perhaps most—are unwilling to accept the reality of these
phenomena. They don‘t believe that the data are sufficiently convincing. The
reality of psi powers is still open to question. (Adapted: Psychology: A Self-Teaching Guide Frank J. Bruno).
(Sumber: Catatan Materi Kuliah Reading: English for Psychology of Student)
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