ASSIGNMENT
SUBMITTED BY :-SRISHTI GAUR
2017/604
PERCEPTION
In our interaction with the physical outside world, it is necessary to process information from it
for the purpose of making sense of the world and also making ourselves safe and reassured.This
process of sensing the outside world is completed by our perception, which, with our sensory
organs, allows us to recognize and identify the existence of all kinds of stimuli and then evaluate
and give meanings to them.
Thus, Perception may be defined as the dynamic psychological process responsible for attending
to, organising and interpreting sensory data. 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.”
PERCEPTUAL PROCESSING
Sensory systems provide the raw materials from which experiences are formed. Our sense organs
do not select what we will be aware of or how we will experience it; they merely transmit as much
information as they can through our nervous system. Yet our experiences are not simply a one-to
one reflection of what is external to our senses. Different people may experience the same sensory
information in radically different ways, because perception is an active, creative process in which
raw sensory data are organized and given meaning.
To create our perceptions, the brain carries out two different kinds of processing functions.
● THE BOTTOM-UP APPROACH
Combination and interpretation of “whole”
⇑
Breakdown/analysis of stimuli (e.g., feature detection)
⇑
Detection of individual stimulus elements
In bottom-up processing, the system takes in individual elements of the stimulus and then
combines them into a unified perception.In other words the term bottom-up (or data-driven)
essentially means that the perceiver starts with small bits of information from the environment and
combines them in various ways to form a percept. A bottom-up model of perception and pattern
recognition might describe your seeing edges, rectangular and other shapes, and certain lighted
regions and putting this information together to “conclude” you are seeing the scene outside your
window. That is, you would form a perception from only the information in the distal stimulus.
For example Your visual system operates in a bottom-up fashion as you read. Its feature detectors
analyze the elements in each letter of every word and then recombine them into your visual
perception of the letters and words.
● Top-down processing
Concept, expectation
⇑
Guides analysis (Yes? No?)
⇑
Interpretation of incoming stimuli
On the other hand, `top-down' phase concerns the mental processing that allows us to order,
interpret and make sense of the world around us.Basically in top-down (also called theory-driven
or conceptually driven) processing, the perceiver’s expectations, theories, or concepts guide the
selection and combination of the information in the pattern-recognition process. One of the key
characteristics of top-down processing concerns our need to make sense of our environment and
our search for meaning.
Top-down processing is occurring as you interpret the words and sentences constructed by the
bottom-up process. Here you make use of higher-order knowledge, including what you have
learned about the meaning of words and sentence construction. Indeed, a given sentence may
convey a different personal meaning to you than to another person if you relate its content to some
unique personal experiences. Top-down processing accounts for many psychological influences
on perception, such as the roles played by our motives, expectations, previous experiences, and
cultural learning.
PERCEPTION: THE FOCUS OF OUR ATTENTION
By shifting the focus of our attention, we may suddenly notice smells, tastes, and tactile sensations
that were outside our awareness only moments ago. One thing is certain—we cannot absorb all of
the available sensory information in our environment. Thus, we selectively attend to certain aspects
of our environment while relegating others to the background (Johnston & Dark, 1986). Selective
attention has obvious advantages, since it allows us to maximize information gained from the
object of our focus while reducing sensory interference from other irrelevant sources (Matlin &
Foley, 1992).
Attention, involves two processes of selection: (1) focusing on certain stimuli and (2) filtering out
other incoming information (Luck & Vecera, 2002). These processes have been studied
experimentally through a technique called shadowing. Shadowing experiments demonstrate that
we cannot attend completely to more than one thing at a time. But we can shift our attention rapidly
back and forth between the two messages, drawing on our general knowledge to fill in the gaps
(Bonnel & Hafter, 1998; Sperling, 1984).
Inattentional Blindness
In the visual realm, scientists have coined the term inattentional blindness to refer to the failure of
unattended stimuli to register in consciousness (Mack, 2003). We can look right at something
without “seeing” it if we are attending to something else. In one study, several experienced pilots
training on flight simulators were so intent on watching the landing instruments, such as the
airspeed indicator on the plane’s windshield, that they directed their plane onto a runway
containing another aircraft (Haines, 1991). Inattentional blindness is surely relevant to findings
that cell phone conversations significantly reduce driving performance in experimental studies
(e.g., Golden et al., 2003).
Environmental and Personal Factors in Attention
Attention is strongly affected by both the nature of the stimulus and by personal factors. Stimulus
characteristics that attract our attention include intensity, novelty, movement, contrast, and
repetition. Advertisers use these properties in their commercials and packaging. Internal factors,
such as our motives and interests, act as powerful filters and influence which stimuli in our
environment we will notice. For example, when we are hungry, we are especially sensitive to food
related cues. A botanist walking through a park is especially attentive to the plants; a landscape
architect attends primarily to the layout of the park.
People are especially attentive to stimuli that might represent a threat to their well-being, a
tendency that would clearly have biological survival value (Izard, 1989; Oehman et al., 2001). A
study by Christine and Ranald Hansen (1988) illustrates this tendency. They presented slides
showing groups of nine people. In half of the pictures, all of the people looked either angry or
happy. In the other half, there was one discrepant face, either an angry face in a happy crowd or a
happy face in an angry crowd. Participants were asked to judge as quickly as possible whether
there was a discrepant face in the crowd, then press “yes” or “no” buttons attached to electrical
timers. The dependent variable was the length of time required to make this judgment, measured
in milliseconds (thousandths of a second).
The results,, showed that participants were much faster at detecting a single angry face in an
otherwise happy crowd than at finding a happy face in an angry crowd. It was as if the angry face,
which the experimenters assumed to have threat value, jumped out of the crowd when the stimuli
were scanned. Attentional processes are thus based both on innate biological factors and on past
experiences that make certain stimuli important or meaningful to us.
PERCEPTUAL ORGANIZATION
The process by which we structure the input from our sensory receptors is called perceptual
organization. Aspects of perceptual organization were first studied systematically in the early
1900s by Gestalt psychologists—German psychologists intrigued by certain innate tendencies of
the human mind to impose order and structure on the physical world and to perceive sensory
patterns as well-organized wholes, rather than as separate, isolated parts (Gestalt means “whole”
in German). These scientists outlined several principles that influence the way we organize basic
sensory input into whole patterns (gestalts). We could say that the Gestalt psychologists changed
our perceptions about the nature of perception.
The Gestalt theorists emphasized the importance of figure-ground relations, our tendency to
organize stimuli into a central or foreground figure and a background. In vision, the central figure
is usually in front of or on top of what we perceive as background. It has a distinct shape and is
more striking in our perceptions and memory than the background. We perceive borders or
contours wherever there is a distinct change in the color or brightness of a visual scene, but we
interpret these contours as part of the figure rather than background.
One stimulus, two perceptions. This reversible figure illustrates alternating figure-ground
relations. It can be seen as a vase or as two people facing one another. Whichever percept exists
at the moment is seen as figure against background.
In addition to figure-ground relations, the Gestalt psychologists were interested in how separate
stimuli come to be perceived as parts of larger wholes. They suggested that people group and
interpret stimuli in accordance with four Gestalt laws of perceptual organization: similarity,
proximity, closure, and continuity.
Gestalt perceptual laws. Among the Gestalt principles of perceptual organization are the laws of
(a) similarity, (b) proximity, (c) closure, and (d) continuity. Each principle causes us to organize
stimuli into wholes that are greater than the sums of their parts.
The Gestalt law of similarity, which says that when parts of a configuration are perceived as
similar, they will be perceived as belonging together. The law of proximity says that elements that
are near each other are likely to be perceived as part of the same configuration. Thus, most
A spiral that isn’t. Fraser’s spiral illustrates the Gestalt law of continuity. If you follow any part
of the “spiral” with a pencil, you will find that it is not a spiral at all but a series of concentric
circles. The “spiral” is created by your nervous system because that perception is more
consistent with continuity of the individual elements.
people perceive as three sets of two lines rather than six separate lines. The law of closure, which
states that people tend to close the open edges of a figure or fill in gaps in an incomplete figure, so
that their identification of the form (in this case, a circle) is more complete than what is actually
there. Finally, the law of continuity holds that people link individual elements together so they
form a continuous line or pattern that makes sense. Or consider Fraser’s spiral, as shown which is
not really a spiral at all! .We perceive the concentric circles as a spiral because, to our nervous
system, a spiral gives better continuity between individual elements than does a set of circles. The
spiral is created by us, not by the stimulus.
PERCEPTION AS HYPOTHESIS TESTING
Recognizing a stimulus implies that we have a perceptual schema—a mental representation or
image containing the critical and distinctive features of a person, object, event, or other
perceptual phenomenon. Schemas provide mental templates that allow us to classify and identify
sensory input in a top down fashion.
Perception is, in this sense, an attempt to make sense of stimulus input, to search for the best
interpretation of sensory information we can arrive at based on our knowledge and
experience.Richard L. Gregory (1966, 2005) suggested that each of our perceptions is essentially
a hypothesis about the nature of the object or, more generally, the meaning of the sensory
information. The perceptual system actively searches its gigantic library of internal schemas for
the interpretation that best fits the sensory data.
Staring at this Necker cube for a while; the front of the cube will suddenly become the back, and
it will appear as if you’re viewing the cube from a different angle.
In some instances, sensory information fits two different internal representations, and there is not
enough information to permanently rule out one of them in favor of the other. For example,
examine the Necker cube, as shown above. If you stare at the cube for a while, you will find that
it changes before your very eyes as your nervous system tries out a new perceptual hypothesis.
PERCEPTUAL SETS
We have seen how the perceptual process selects incoming stimuli and organises them into
meaningful patterns. It has also been shown that this processing is influenced by learning,
motivation and personality -factors which give rise to expectations. These expectations, in turn,
make us more ready to respond to certain stimuli in certain ways and less ready to respond to
others. This readiness to respond is called the individual's perceptual set - a readiness to perceive
stimuli in a particular way.
A perceptual set is an individual's predisposition to respond to events in a particular manner. A
perceptual set is also known as a mental set. As we tend to perceive what we expect to perceive,
this can also be called our perceptual expectations. We must accept the fact that two people can
observe the `same' thing but perceive it in quite different ways. Many organisational problems,
and particularly communication problems are created by failure to appreciate this feature of the
perceptual process. For example, top management of an organisation may perceive that junior
employees are overreacting to trivial issues and may dismiss their complaints lightly. On the other
hand, the junior employees may perceive that their grievances are genuine and that the top
management are simply not taking them seriously. In a situation like this, it makes little sense to
ask whose perceptions are correct. The starting point for resolving issues such as this must lie with
the recognition that different people hold different, but equally legitimate, views of the same set
of circumstances.
We each have a perceptual world that is selective and partial which concentrates on features of
particular interest and importance to us. The individual's perceptual world is their personal internal
image, map or picture of their social, physical and organisational environment. Through the
processes of learning, motivation and personality development, we each have different
expectations and different degrees of readiness to respond to objects, people and events in different
ways.
It may be noted here that our perceptions, that is the meanings that we attach to the information
available to us, shape our actions. Behaviour in an organisation context can usually be understood
once we understand the way in which the individual perceives that context. Cultural factors also
play a significant role in determining how we interpret available information and experience.
Perceptual learning and development take place in the context of socio-cultural environment. It
therefore, expected that the socio-cultural background of the individual will influence his/her
perceptions. Accordingly, the nature of perceptual organisations will vary.
Therefore, it is clear that to understand an individual's behaviour, we need to know something of
the elements in their perceptual world and the pattern of information and other cultural influences
that have shaped that world. To change an individual's behaviour, therefore, we first have to
consider changing their perceptions through the information and experiences available to them.
PERCEPTUAL CONSTANCIES
When a closed door suddenly swings open, it casts a different image on our retina, but we still
perceive it as a door. Our perceptual hypothesis remains the same. Were it not for perceptual
constancies, which allow us to recognize familiar stimuli under varying conditions, we would have
to literally rediscover what something is each time it appeared under different conditions.
In vision, several constancies are important.
● Shape Constancy
The principle of shape constancy refers to the fact that the perceived shape of an object does not
alter as the image the object casts on the retina changes. For example, all of us know that coins are
round; yet we rarely see them that way. Flip a coin into the air: although you continue to perceive
the coin as being round, the image that actually falls onto your retina constantly shifts from a circle
to various forms of an ellipse.
The principle of shape constancy allows us to recognize this object as a rectangular door,
despite the fact that the image cast on the retina changes as the door opens or closes.
● Size Constancy
The principle of size constancy relates to the fact that the perceived size of an object remains the
same when the distance is varied, even though the size of the image the object casts on the retina
changes greatly. For example, seeing a friend walking toward you, though still several blocks
away. Distant objects—including cars, trees, and people—cast tiny images on your retina. Yet we
perceive them as being of normal size. Two factors seem to account for this tendency: size–
distance invariance and relative size.
The principle of size–distance invariance suggests that when estimating the size of an object, we
take into account both the size of the image it casts on our retina and the apparent distance of the
object.
Size constancy based on distance cues causes us to perceive the person in the background as
being of normal size. When the same stimulus is seen in the absence of the distance cues, size
constancy breaks down. The two person no longer look similar in size, nor do the photographic
images of the man in the shirt.
● Brightness Constancy
The principle of brightness constancy refers to the fact that we perceive objects as constant in
brightness and color, even when they are viewed under different lighting conditions. Thus, we will
perceive a sweater as dark green whether indoors or outdoors in bright sunlight. Brightness
constancy apparently prevails because objects and their surroundings are usually lighted by the
same illumination source, so changes in lighting conditions occur simultaneously for both the
object and its immediate surroundings.
In broad daylight the shirt will appear to be much brighter than the pants. But if the sun is
covered by thick clouds, even though the pants and shirt have less light to reflect than previously,
the shirt will still appear to be just as much brighter than the pants as before
PERCEPTION OF DEPTH, DISTANCE AND MOVEMENT
The ability to adapt to a spatial world requires that we make fine distinctions involving distances
and the movement of objects within the environment. Humans are capable of great precision in
making such judgments.
Depth and distance perception
One of the more intriguing aspects of visual perception is our ability to perceive depth. The retina
receives information in only two dimensions (length and width), but the brain translates these cues
into three-dimensional perceptions. It does this by using both monocular depth cues, which require
only one eye, and binocular depth cues, which require both eyes.
Monocular cues to depth or distance include the following:
1. Size cues: The larger the image of an object on the retina, the larger the object is judged to be;
in addition, if an object is larger than other objects, it is often perceived as closer.
2. Linear perspective: Parallel lines appear to converge in the distance; the greater this effect, the
farther away an object appears to be.
3. Texture gradient: The texture of a surface appears smoother as distance increases.
4. Atmospheric perspective: The farther away objects are, the less distinctly they are seen—smog,
dust, haze get in the way.
5. Overlap (or interposition): If one object overlaps another, it is seen as being closer than the one
it covers.
6. Height cues (aerial perspective): Below the horizon, objects lower down in our field of vision
are perceived as closer; above the horizon, objects higher up are seen as closer.
7. Motion parallax: When we travel in a vehicle, objects far away appear to move in the same
direction as the observer, whereas close objects move in the opposite direction. Objects at different
distances appear to move at different velocities.
We also rely heavily on binocular cues—depth information based on the coordinated efforts of
both eyes.
Binocular cues for depth perception stem from two primary sources:
1. Convergence: In order to see close objects, our eyes turn toward one another; the greater this
movement, the closer such objects appear to be.
2. Retinal disparity (binocular parallax): Our two eyes observe objects from slightly different
positions in space; the difference between these two images is interpreted by our brain to provide
another cue to depth.
These lists of monocular and binocular cues are by no means exhaustive. By using the wealth of
information provided by these and other cues (Schiffman, 1990), we can usually perceive depth
and distance with great accuracy.
Perception of movement
The perception of movement is a complex process, sometimes requiring the brain to integrate
information from several different senses.
The primary cue for perceiving motion is the movement of the stimulus across the retina (Sekuler
et al., 2002). Under optimal conditions, a retinal image need move only about one fifth the diameter
of a single cone for us to detect movement (Nakayama & Tyler, 1981). The relative movement of
an object against a structured background is also a movement cue (Gibson, 1979). For example, if
you fixate on a bird in flight, the relative motion of the bird against its background is a strong cue
for perceived speed of movement.
The illusion of smooth motion can be produced if we arrange for the sequential appearance of two
or more stimuli. Gestalt psychologist Max Wertheimer (1912) demonstrated this in his studies of
stroboscopic movement, illusory movement produced when a light is briefly flashed in darkness
and then, a few milliseconds later, another light is flashed nearby. If the timing is just right, the
first light seems to move from one place to the other in a manner indistinguishable from real
movement.
Stroboscopic movement is also the principle behind motion pictures, which consist of a series of
still photographs, or frames, that are projected on a screen in rapid succession with dark intervals
in between. The rate at which the frames are projected is critical to our perception of smooth
movement. Early movies, such as the silent films of the 1920s, projected the stills at only 16 frames
per second, and the movements appeared fast and jerky. Today the usual speed is 24 frames per
second, which more perfectly produces an illusion of smooth movement. Television presents at 30
images per second.
ILLUSIONS: FALSE PERCEPTUAL HYPOTHESES
Our analysis of perceptual schemas, hypotheses, sets, and constancies allows us to understand
some interesting perceptual experiences known as illusions, compelling but incorrect perceptions.
Such perceptions can be understood as erroneous perceptual hypotheses about the nature of a
stimulus. Illusions are not only intriguing and sometimes delightful visual experiences, but they
also provide important information about how our perceptual processes work under normal
conditions (Gregory, 2005).
Ironically, most visual illusions can be attributed to perceptual constancies that ordinarily help us
perceive more accurately (Frisby, 1980). For example, size constancy results in part from our
ability to use distance cues to judge the size of objects. But as we saw in the discussion of the
moon illusion, distance cues can sometimes fool us. In the Ponzo illusion, shown , the depth cues
of linear perspective (the tracks converging) and height of the horizontal plane provide distance
cues that make the upper bar appear farther away than the lower bar. Because it seems farther
away, the perceptual system concludes that the bar in the background must be larger than the bar
in the foreground, despite the fact that the two bars cast retinal images of the same size.
Two examples of the Ponzo illusion. Which lines in (a) and (b) are longer? Measure them and
see. The distance cues provided by the converging railroad tracks and the walls affect size
perception and disrupt size constancy.
Distance cues can be manipulated to create other size illusions. To illustrate this, Adelbert Ames
constructed a special room. Viewed through a peephole with one eye, the room’s scene presents a
startling size reversal. Our perceptual system assumes that the room has a normal rectangular shape
because, in fact, most rooms do. Monocular depth cues do not allow us to see that, in reality, the
left corner of the room is twice as far away as the right corner. As a result, size constancy breaks
down, and we base our judgment of size on the sizes of the retinal images cast by the two people..
A size illusion. The Ames Room produces a striking size illusion because it is designed to appear
rectangular. The room, however, is actually trapezoidal, and the figure on the left is actually
much farther away from the viewer than the one on the right and thus appears smaller. We
perceive the boy as if he were the purple figure, making him appear very large.
The study of perceptual constancies shows that our perceptual hypotheses are strongly influenced
by the context, or surroundings, in which a stimulus occurs. The figure below shows some
examples of how context can produce illusory perceptions.
The long lines are actually parallel, but the small lines make them appear crooked.
The Müller-Lyer illusion. Which line, a or b, is longer? Compare them with a ruler.
Some of the most intriguing perceptual distortions are produced when monocular depth cues are
manipulated to produce a figure or scene whose individual parts make sense but whose overall
organization is “impossible” in terms of our existing perceptual schemas. Figure below this shows
three impossible figures. In each case, our brain extracts information about depth from the
individual features of the objects, but when this information is put together and matched with our
existing schemas, the percept that results simply doesn’t make sense. The “devil’s tuning fork,”
for example, could not exist in our universe. It is a two-dimensional image containing paradoxical
depth cues. Our brain, however, automatically interprets it as a three-dimensional object and
matches it with its internal schema of a fork—a bad fit indeed. The never-ending staircase provides
another compelling example of an impossible scene that seems perfectly reasonable when we focus
only on its individual elements.
Things that couldn’t be. Monocular depth cues are cleverly manipulated to produce an
impossible triangle, a never-ending staircase, and the “devil’s tuning fork.”
REFERENCES
● Atkinson, R. L., Atkinson, R. C., Smith, E. E., Bem, D. J. & Hilgard, E. R. (2013).
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● Baron, R. & Misra. G. (2013). Psychology. Pearson.
● Chadha, N.K. & Seth, S. (2014). The Psychological Realm: An Introduction. Pinnacle
Learning, New Delhi
● Ciccarelli, S. K., & Meyer, G. E. (2010). Psychology: South Asian Edition. New Delhi:
Pearson Education
● Passer, M.W. & Smith, R.E. (2010). Psychology: The science of mind and behaviour. New
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