WHAT IS PERCEPTION?

Perception refers to the way the world looks. sounds. feels. tastes, or smells. In other words,
perception can be defined as whatever is experienced by a person.

The sensory-in put. patterns provide only the raw material for experience. For example, when
we perceive the visual riches of an art museum, people's faces, television, or a conversation,
active processes work on the sensorv input to transform it into what we experience. Thus,
perception -our experience of the world---arises from sensory input plus the ways we process
the sensory information

The word “perception” comes from the Latin words perceptio, percipio, and means
“receiving, collecting, action of taking possession, and apprehension with the mind or
senses.”

SENSATION AND PERCEPTION:

Sensation refers to the initial detection of energy from the physical world. The study of
sensation generally deals with the structure and processes of the sensory mechanism and the
stimuli that affect those mechanism.

Perception, on the otherhand, involves higher-order cognition in the interpretation of the

sensory information.

Basically, sensation refers to the initial detection of stimuli; perception to an interpretation of

the things we sense.

When we read a book, listen to our iPod, get a massage, smell cologne, or taste sushi, we
experience far more than the immediate sensory stimulation. Sensory events are processed
within the context of our knowledge of the world, on culture, expectations, and even who we
are with at the time. These give meaning to simple sensory experiences—that is perception.

WILLIAM JAMES ON PERCEPTION:

Many years ago, the famous American psychologist William James put it this way: "Part of
what we perceive comes through the senses from the object before us; another part ... always
comes, ... out of our own head." The "out of our own head" part of this quotation refers to the
active processing of sensory input that makes our experience of the world what it is
 TYPES OF PERCEPTION:

A. FORM PERCEPTION:

Gestalt concepts of perception:

● Figure and Ground: The most important things in form perception is the the
recognition of a figure on a ground. Our visual system is designed to impose
organization on the richly complicated visual world (Geisler & Super, 2000; Palmer,
2003)

The figure has a distinct shape with clearly defined edges. In contrast, the ground is the
region that is “left over,” forming the background. As gestalt psychologists pointed out, the
figure has a definite shape, whereas the ground simply continues behind the figure.

Hebb in his book ‘The organization of behavior’ pointed out that the primitive unit of a figure
is its simplest aspect. By this he means that a bounded area, the figure will be seen as a unit,
standing out from the background, even before the figure is recognized as a figure, before it
has identity.

CONTOURS IN VISUAL PERCEPTION: We can separate forms from the general ground
in our visual perception only because we can perceive contours. (From Coren. 1972; based on
Kanizsa, 1955). Contour are formed whenever a marked difference occurs in the brightness
or color of the background. Contours give shape to the objects in our visual world because
they mark one object off from another or they mark an object off from the general ground.

While differences in energy levels of light across the retina are involved in the formation of
most contours in everyday experience, it has been found that contours can sometimes be seen
without any energy difference at all on the two sides of the contour (Kanizsa, 1976; Coren,
1972). These are the so-called subjective contours (illusory contours)

DIFFERENCE BETN FIG AND GRND: RUBIN: The figure has form, while the ground is
relatively formless, or if ground has form it is due to some other figuration upon it and not to
the contour separating it from the figure. The ground seems to extend continuously behind
the figure and not to be interrupted by the figure. The figure has some of the character of a
thing, whereas the ground appears like unformed material. The figure tends to appear in front,
the ground behind. The figure is more impressive, better remembered, and more apt to
suggest meaning.
AMBIGUOUS FIG-GRND RELN:

In an ambiguous figure–ground relationship, the figure and the ground reverse from time to
time, so that the figure becomes the ground and then becomes the figure again

EXPLANATION OF REVERSAL: The explanation for these figure–ground reversals seems

to have the following two components:

1. The neurons in the visual cortex become adapted to one figure, such as the “faces”
version of Figure, we are more likely to see the alternative or “vase” version
2. Furthermore, people try to solve the visual paradox by alternating between two
reasonable solutions (Gregory, 2004a; Long & Toppino, 2004; Toppino & Long,
2005).

● Gestalt: Organization in form perception: When several objects are present in the
visual field, we tend to perceive them as organized into patterns or groupings. Such
organization was studied intensively in the early part of this century by the Gestalt
psychologists

Gestalt psvchologists said that "the whole is more than the sum of its parts." This
simply means that what is perceived has its own new properties, properties that
emerge from the organization which takes place.

LAWS OF PERCEPTUAL ORGANIZATION:

● The law of Proximity, or nearness: The law of proximity says that items which are
close together in space or time tend to be perceived as belonging together or forming
an organized group.
● The law of Similarity: The similar objects tend to be organized together
● The law of good figure or the law of pragnanz: The law of good figure says that there
is a tendency to organize things to make a balanced or symmetrical figure that
includes all the parts. In this case, such a balanced figure can be achieved only by
using all the dots and rings to perceive a six-pointed star
 ● The law of Continuation: The tendency to perceive a line that starts in one wav as
continuing in the same wav
● The law of Closure: The law of closure makes our perceived world of form more
complete than the sensory stimulation that is presented. The law of closure refers to
perceptual processes that organize the perceived world by filling in gaps in
stimulation
● The law of Common fate: Objects that move simultaneously in the same direction are
seen as a group. They possess a sort of similarity in their sameness of motion.

B. TYPE: DEPTH PERCEPTION:CONCEPT: Scientists were interested to know how we

perceive three-dimensional world with two-dimensional retina. They observe that we can
make use of information, or cues, in the sensory input to "generate" the three-dimensional
world that we see.

DEPTH PERCEPTION: CUES: There are the following two types of cues we use in depth
perception:

● The monocular ("one-eyed") cues for depth perception: the cues received by each
eye separately.

These cues are the ones used by painters to give us a three-dimensional experience from a flat
painting. Different monocular cues are mentioned below:

● Linear Perspective: The distances separating the images of far objects appear to be
smaller. Imagine that you are standing between railroad tracks and looking off into the
distance. The ties would seem to gradually become smaller, and the tracks would
seem to run closer and closer together until they appeared to meet at the horizon
● Clearness: Aerial perspective: In general, the more clearly, we see an object, the
nearer it seems. A distant mountain appears farther away on a hazy day than it does
on a clear dav because haze in the atmosphere blurs fine details and we can see only
the larger features. Ordinarily, if we can see the details, we perceive an object as
relatively close; if we can see only its outline, we perceive it as relatively far away
● Interposition: Another monocular cue is interposition, which occurs when one object
obstructs our view of another. When one object is completely visible while another is
partly covered by it, the first object is perceived as neare
● Shadows: The pattern of shadows or highlights in an object is very important in
giving an impression of depth
 ● Gradients of Texture: A gradient is a continuous change in something-a change
without abrupt transitions. In some situations, we can use the continuous gradation of
texture in the visual field as a cue for depth (Gibson, 1950). The regions closest to the
observer have a coarse texture and many details; as the distance increases, the texture
becomes finer and ' finer. This continuous gradation of texture gives the eye and brain
information that can be used to produce an experience, or perception, of depth.
● Movement: When we move our head, we will observe that the objects in our visual
field move relative to us and to one another. If we watch closely, we will find that
objects nearer to us than the spot at which we are looking-the fixation point-move in
a direction opposite to the direction in which our head is moving. On the other hand,
objects more distant than the fixation point move in the same direction as our head
moves. Thus, the direction of movement of objects when we turn our heads can be a
cue for the relative distance of objects. Furthermore, the amount of movement is less
for far objects than it is for near ones. Of course. as is the case with all depth cues, we
do not usually think about this information; we use it automatically.

● The binocular ("two-eyed") cues: The cues received from both eves working
together: We look out at the world with both eyes simultaneously, and we are thus
able to add binocular cues for· depth perception to the monocular ones. By far the
most important binocular cue comes from the fact that the two eves-the
retinas-receive slightly different, or disparate, views of the world. Therefore, this cue
is known as retinal disparity; It is the difference in the images falling on the rctinas of
the two eves.
A. RETINAL DISPARITY: The fovea in the center of the retina is much more
sensitive than is the rest of the retina . When we look at an object, we fixate
our eyes-point them, in a manner of speaking--so that the image of the object
falls mostly on each fovea.
B. STEREOSCOPIC VISION: Stereoscopic vision or Stereopsis (from stereo
meaning solidity, and opsis meaning vision or sight) is the process in visual
perception leading to perception of stereoscopic depth. In turn, stereoscopic
depth is the sensation of depth perception that emerges from the fusion of the
two slightly different projections of the world on the two retinas.

**But since the two eyes are separated from each other by about 65 millimeters, they get
slightly different views of the object, and the two images are not the same Moreover, and this
is the main point, the images are more dissimilar when the object is close than when it is far
in the distance. In other words, within limits, the closer an object is, the greater is the retinal
disparity. The correspondence between distance and the amount of disparity is the reason
retinal disparity can be used as a depth cue.

C. MOTION PARALLAX: Motion parallax is one of the cues used in depth

perception in which near objects seem to move faster than objects that are
further away. Motion parallax occurs when objects that are at different
distances from us appear to move at rates that are different while we are
moving.

C. TYPE: MOVEMENT PERCEPTION:

a. APPARENT AND REAL MOTION: When perceived motion occurs without any
energy movement across the receptor surface. This type of motion is called apparent
motion. Furthermore. the perception of the actual physical movement of objects in the
world- real motion-is like all perception: it involves active processing of the sensory
stimulation.
b. CONSTANCY OF REAL MOTION PERCEPTION: We need movement constancy
in order to adapt to events in the visual world. Perceived velocity depends on the rate
at which an object moves relative to its background, not on the absolute velocity of
the image across the retina. Since the relationship between an object and its
background stays relatively constant with distance-as one changes, the other does,
too-perceived velocity also remains fairly constant.
c. THE BRAIN COMPUTER & REAL MOTION PERCEPTION: There are cells in the
brain that are vigorously excited by movement. In the simple case of movement
across a stationary retina. These "movement-detecting" cells probablv provide the
basis for our perception of real motion. But retinal images also move when we move
our eyes, head, and body. Somehow we must be able to tell whether the retinal image
moved because we moved or because something "out there'' moved. We would have a
very hard time adapting to the world if we could not tell which was which.

The concept of a "brain comparator" has been postulated to explain how it is possible
for us to differentiate between the real motion of an object and motion caused by our
own movement. The brain Comparator is a system which compares information about
muscle movements with information about movements of the retinal image.

Movement commands to the eye muscles go both to the eve muscles themselves and
to the brain comparator ; in this wav, the comparator has information that a movement
is about to occur before it actually occurs. When the eye movement occurs and the
 retinal image moves. The movement signals from the retina are fed into the
comparator, where they are matched against the information the comparator already
has about eye movements. The brain comparator "evaluates" the moving retinal image
as due to eye movements and cancels the perception of movement.

On the other hand, if the comparator has no information about eye movements, as
when an image moves over a stationary eye, the perception of movement is not
cancelled

d. APPARENT MOTION: Apparent motion is movement perceived in the absence of

physical movement of an image across the retina. In other words, with the eyes, head,
and body steady, and with no physical movement of an object, motion is still
perceived.

APPRENT MOTION: TYPES:

1. Stroboscopics motion: Stroboscopic motion, the kind seen in movies and on

television, is a common example of apparent motion. A movie projector
simply throws Successive pictures of a moving scene onto a screen. when you
examine the separate frames. you see that each is a still picture slightly
different from the preceding one. When the frames are presented at the right
speed. You perceive continuous, smooth motion.

Many psychologists who study perception now believe that stroboscopic

motion results from information processing by the brain that is similar to that
which occurs when real motion is perceived. In movies, for instance, the brain
receives information from different parts of the retina, just as it does when
physical movement causes stimulation to move across the retina.

An object is first seen in one location, and then, very soon after, appears at a
slightly different part of the retina, just as it would if it were actually moving.
The brain "interprets" this information as movement, showing once again the
role of sensorv-input processing in the perception of the world.

2. Autokinetic effect: The autokinetic effect is another example of apparent

motion. If a person stares at, or fixates on, a small stationary spot of light in a
completely dark room, the spot will eventually appear to move. Such apparent
 motion can be large and dramatic, and it can be influenced by suggestion.
Movements of the eyes have an influence on the autokinetic effect, but they do
not seem to account for it
3. Induced movement: Induced movement occurs if a stationary spot or object is
perceived as moving when its frame or background moves. For example, the
moon is often perceived as "racing" through a thin laver of clouds. The
movement of the framework of clouds "induces" movement in the relatively
stationary moon.

PERCEPTUAL CONSTANCY? The stability of the environment as we perceive it is

termed perceptual constancy.

● Size Constancy: The size of the representation, or "image," of an object on the retina
of the eye depends upon the distance of the object from the eye; the farther away it is,
the smaller the representation.

An object of known size, like a man or an auto, is always judged to be same size, even
though the retinal image may vary.

Contributing to this constancy is a great deal of additional information we have about

the circumstances: You know something about the distance of the friend from us; we
perceive the changes that take place in other objects as we approach our friend; and
we know how large our friend is supposed to be-the friend's assumed size. Therefore,
distance and background information maintaining size constancy .

The importance of distance and background information in maintaining size

constancy was shown in a classic experiment by A. H. Holway and E. G. Boring in
the 1940s (Holway & Boring, 1941).

They used ambiguous stimuli-disks of light-which could have no real assumed size,
and they changed the amount of distance and background information available to the
subjects in the experiment. They found that size constancy decreased as the distance
and background information available to the subjects decreased. In other words, the
subjects perceived the size of a disk of light more in accordance with the size of the
retinal representation when they lacked information about distance and background.

One interpretation of this result might be that people somehow automatically use
information about distance and background to "correct" the size of their retinal
 representations, thus keeping their perceptions relatively constant. Another
interpretation is that no "correction" is . According to this interpretation (Gibson,
1950). perceptual size constancy results when an object and its background change
together in such a way that the relationship between them stays the same.

Our knowledge of the size of a familiar object-the assumed size-sometimes be an

important factor in size constancy, especially under conditions in which other
information is not available or is ambiguous. But, under everyday conditions of
perception, conditions in which distance and background information are available
and unambiguous, the assumed size of familiar objects is not an important factor in
maintaining size constancy(Fillenbaum et al., 1965)

EUCLIDS LAW IN SIZE CONSTANCY: a=A/D

● a= retinal area
● A=object
● D= Distance

**The retinal area subtended by an object varies inversely with its distance.

EMMERTS LAW: The judged size of the image is proportional to the distance

● Shape Constancy: Shape constancy means familiar object keeps its perceived shape
despite major changes in retinal stimulation due to changes in its orientation. For
instance, we perceive the door as a rectangle even if we are receiving different
sensory images due to changes in its orientation.
● Colour Constancy: Colour Constancy is when the perceived color of objects does not
vary much with changes in the illumination, even though these changes cause huge
changes in the spectral light entering the eye
● Brightness constancy: Visual objects also appear constant in their degree of whiteness,
grayness. or blackness, even though the amount of physical energy reflected from
them mav change enormously. Our experience of brightness stays relatively constant
despite great changes in the amount of physical energy reaching o eyes. For example,
objects or surfaces that appear white in a bright light are still perceived as white in
dim illumination. Similarly, what looks black to us in dim light still looks black in
intense light. Coal looks black even in very bright sunlight, while snow continues to
look white even at night.

We have brightness constancy because in most situation. When the illumination

changes, it changes over the whole field: The physical energy ratio between an object
and its surround stays constant. For example, if I turn up the lights in my room. the
cover of the book on my desk looks just as bright as it did before because the ratio of
the illumination falling on the book cover and that falling on its surround has not
changed. In other words. unchanged-brightness ratios give constant brightness
experiences, or brightness constancy.
 ROLE OF MOTIVATION IN PERCEPTION:

In the late 1940s and through the 1950s, many psychologists turned their attention to the idea
that motives and needs influence perception. This viewpoint was called the "new look" in
perception. Although many of the "new look" experiments were flawed and some of the
specific theoretical ideas of the "new look" have been sharply criticized, the general idea that
individual differences in motives and needs affect perception persists. In other words, we may
attend to and organize sensory inputs in ways that match our needs. For example, people who
are hungry or thirsty, are likely to pay attention to events in the environment which will
satisfy these needs

Projective tests, such as the well-known Rorschach inkblot test , capitalize on the influences
of motivation on perception. The inkblots or pictures used in projective tests are ambiguous;
they can be perceived in any number of ways. The idea is that people's motives will, to some
extent, affect the ways in which they organize and perceive the test stimuli.

ROLE OF LEARNING IN PERCEPTION:

PERCEPTUAL LEARNING: Based on past experiences or any special training we have had,
each of us has learned to emphasize some sensory inputs and to ignore others. Eleanor
Gibson has defined perceptual learning as "an increase in the ability to extract information
from the environment as a result of experience or practice with the stimulation coming from
it" (Gibson,1969).

Gibson gives many examples that show how perception can be molded by learning. She cites
the competence of people trained in various occupations to make perceptual distinctions that
untrained people cannot make. Skill, or artistry, in many professions is based upon the ability
to make these subtle distinctions. Experience is the best teacher for these perceptual skills;
usually, thev cannot be learned from books.

Gibson also points out; the remarkable feats of blind people are often matters of perceptual
learning. It is not that their sensitivity to nonvisual stimulation is greater than that of sighted
people. Instead, blind people learn to extract from the environment information not ordinarily
used by sighted people. For instance, many blind people move around in the world, avoiding
obstacles with surprising ease. Blind people learn to perceive the sound echoes of their
footfalls and cane tappings that bounce back from objects in their paths. Some blind people
even learn to distinguish among various shapes and textures of surfaces by perceiving the
differences in their sound echoes.
DESIGN AND COGNITION:

COGNITION: Cognition, or mental activity, describes the acquisition, storage,

transformation, and use of knowledge. (Attention, Perception, Memory, Problem Solving,
Decision Making, Reasoning, Imagery)

APPLICATION OF GESTALT: Developed in the 20th Century in Europe: human beings

tend to organize whatever they perceive.