Chapter 6: Perception
Selective Attention
At any moment we are conscious of a very limited amount of all that we are capable of experiencing. One
example of this selective attention is the cocktail party effect—attending to only one voice among many.
Another example is inattentional blindness, which refers to our blocking of a brief visual interruption when
focusing on other sights.
Perceptual Illusions
Visual and auditory illusions were fascinating scientists even as psychology emerged. Explaining illusions
required an understanding of how we transform sensations into meaningful perceptions, so the study of
perception became one of psychology’s first concerns. Conflict between visual and other sensory information is
usually resolved with the mind’s accepting the visual data, a tendency known as visual capture.
Perceptual Organization
From a top-down perspective, we see how we transform sensory information into meaningful perceptions when
we are aided by knowledge and expectations.
The early Gestalt psychologists were impressed with the seemingly innate way we organize fragmentary
sensory data into whole perceptions. Our minds structure the information that comes to us in several
demonstrable ways:
Form Perception
To recognize an object, we must first perceive it (see it as a figure) as distinct from its surroundings (the
ground). We must also organize the figure into a meaningful form. Several Gestalt principles—proximity,
similarity, continuity, connectedness, and closure—describe this process.
Depth Perception
Research on the visual cliff revealed that many species perceive the world in three dimensions at, or very soon
after, birth. We transform two-dimensional retinal images into three-dimensional perceptions by using binocular
cues, such as retinal disparity, and monocular cues, such as the relative sizes of objects.
Motion Perception
Our brain computes motion as objects move across or toward the retina. Large objects appear to move more
slowly than smaller objects. A quick succession of images, as in a motion picture or on a lighted sign, can also
create an illusion of movement.
Perceptual Constancy
Having perceived an object as a coherent figure and having located it in space, how then do we recognize it—
despite the varying images that it may cast on our retinas? Size, shape, and lightness constancies describe how
objects appear to have unchanging characteristics regardless of their distance, shape, or motion. These
constancies explain several of the well-known visual illusions. For example, familiarity with the size-distance
relationships in a carpentered world of rectangular shapes makes people more susceptible to the Müller-Lyer
illusion.
Perceptual Interpretation
The most direct tests of the nature-nurture issue come from experiments that modify human perceptions.
Sensory Deprivation and Restored Vision
For many species, infancy is a critical period during which experience must activate the brain’s innate visual
mechanisms. If cataract removal restores eyesight to adults who were blind from birth, they remain unable to
perceive the world normally. Generally, they can distinguish figure from ground and can perceive colors, but
they are unable to recognize shapes and forms. In controlled experiments, animals have been reared with
severely restricted visual input. When their visual exposure is returned to normal, they, too, suffer enduring
visual handicaps.
Perceptual Adaptation
Human vision is remarkably adaptable. Given glasses that shift the world slightly to the left or right, or even
turn it upside down, people manage to adapt their movements and, with practice, to move about with ease.
Perceptual Set
Clear evidence that perception is influenced by our experience—our learned assumptions and beliefs—as well as
by sensory input comes from the many demonstrations of perceptual set and context effects. The schemas we
have learned help us to interpret otherwise ambiguous stimuli, a fact that helps explain why some of us "see"
monsters, faces, and UFOs that others do not.
Perception and the Human Factor
Perceptions vary, and may not be what a designer assumes. Human factors psychologists therefore study how
people perceive and use machines, and how machines and physical environments can be better suited to that
use. Such studies have improved aircraft safety and spawned user-friendly technology.
Is There Extrasensory Perception?
Many believe in or claim to experience extrasensory perception (ESP). To believe in ESP is to believe that the
brain can perceive without sensory input. Most US scientists are skeptical, yet five British universities have
parapsychology departments.
Examples of ESP include astrological predictions and communication with the dead. Three forms of ESP,
telepathy, clairvoyance, and precognition, are deemed the most testable. However, parapsychologists have tried
to documents several forms of ESP but for several reasons, especially the lack of a reproducible ESP effect,
most research psychologists remain skeptical.