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Sensation and Perception

Sensation

Sensation is the primary experience of knowing the world around us. To know, recognize and evaluate the
objects of the world, we need to obtain information about them. This information is gathered through
information gathering system that includes receiving of information through receptor mechanisms in the sense
organs. These mechanisms convert the physical energy of the stimulus into neural energy which is conveyed
through sensory peripheral nervous system to the sensory areas in the brain and thus we have the first-hand
knowledge about the stimulus present in the environment.

This entire channel of process stretching from reception leading to transmission of impulses to the sensory area
of the brain is what we call sensory process and sensing of object is sensation.

We may also define sensation as the lower cognitive process which provides mere awareness of stimulus present
in the environment.

The process of sensation is very simple: Any object present in the environment impinges on the sense organs
that respond to it by producing nerve impulses followed by communicating the same to the corresponding
sensory areas in the brain.

Types of sensation
Sensations are based on different sensory organs and the sense related with it as described below:

1. Visual sensation
Light, the stimulus for visual experience, is considered to be waves of radiant energy emanating from a
source which is seen by us. The sensory organ related to visual sensation is eye.

2. Auditory sensation
Whether it is a piece of music of barking of a dog or a voice of a lady, they just produce sound waves which
are just the stimulus for hearing (audition). The sensory organ responsible for hearing is called ear.

3. Olfactory sensation
Stimuli for olfaction are various chemicals that are carried by air. Smelling is done by our nose.

4. Gustatory sensation
Stimulus for taste is substance soluble in saliva. We taste different things through our tongue. Sensitivity to
different taste stimuli varies from place to place on tongue. While any substance can be detected at almost
any place on the tongue except at the centre of the tongue. Located at the back of the tongue are the taste
buds that are particularly sensitive to bitter substances. Taste buds at the sides of tongue are particularly
sensitive to sour while those at tip of the tongue are especially sensitive to sweet.

5. Tactile sensation(sense of pressure, pain, warmth, and cold)

 Stimulus for pain- any object that causes injury to skin.
 Stimulus for pressure- any object that depresses skin.
 Stimulus for warmth- any object that is warmer than skin itself
 Stimulus for cold- any object that is colder than skin itself.
Sensation of all these is done through our skin, the largest sensory organ or surface of our human body.

Some of the other sensations except the standard five sensations are:

1. Kinesthetic sensation
It is the sensation of movement of body parts and its relative position to other parts. Ability of the person to
do different activities by closing the eyes is due to kinaesthetic sensation.

2. Vestibular sensation
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It is the sensation that tells us which side is up and which side is down. It tells us about the changes in speed
of movement and its rotations.

3. Sixth sense
Sixth sense is something we call the gut instinct. At times we sense things that are neither seen, heard, felt,
tasted, nor smelled. We simply feel like something is happening and it happens.

Attention

We are surrounded by many stimuli but it is just not possible to react to all stimuli of environment at any given
moment. Attention is defined as concentration of consciousness upon one object rather than upon another.
Attention is a selective process in that we respond selectively in terms of our need, states, interests, attitudes.

Perception

We need to know what sensation is in order to understand perception. Sensation is our first awareness of some
outside stimulus. An outside stimulus activates sensory receptors which in turn produces electrical signals that
are transformed by the brain into meaningless bits of information.

While perception is the experience we have after our brain assembles and combines thousands of individual
meaningless sensations into meaningful pattern or image. However, our perceptions are rarely exact replicas of
the original stimuli; rather it is usually changed, biased, colored or distorted by our unique set of experiences.
Thus, perceptions are our personal interpretations of the real world.

Simply perception may be defined as the process by which sensory input is so interpreted as to make it
meaningful. Charles G Morris, 1979 define perception as all the processes involved in creating meaningful
patterns out of a jumble of sensory impressions fall under the general category of perception.

Edmund Fastino and G.S. Renolds, 1975 explain that perception is the organizing process by which we interpret
our sensory input.

The mechanism through which the organism converts a sense impression to perception by adding
meaning to it is called the process of perception. Thus, sensation is first step in the process of
perception. Perception, in fact starts with sensation. Though, without sensation, there cannot be
perception, all sensation may not lead to perception because perception is a selective process.

It is neither possible nor necessary to perceive everything. Our sense organs translate physical
energy from the environment into electrical impulses processed by the brain. For example, light, in
the form of electromagnetic radiation, causes receptor cells in our eyes to activate and send signals
to the brain. But we do not understand these signals as pure energy. The process of perception
allows us to interpret them as objects, events, people, and situations. Perception involves following
processes:

a) Receptor process
b) Symbolic process
c) Affective process

a) Receptor process – The first process in perception is the receptor process. A stimulus in the
environment stimulates one or the several sense organs. For example, a rose may stimulate
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three different receptor cells. It may stimulate the visual receptors, olfactory receptors and the
tactual sensations.
b) Symbolic process – Sensory stimulation arouses certain neural activities which have their traces
in the nervous system. They are known as neural traces. These traces act as symbols or
substitutes for the original stimulus or experiences. They are called images.
When we perceive something, then the symbolic images about that object in the brain becomes
active. The symbolic images are associated with the object in the external environment. It helps
us in interpretation of the object. For perception, both present sensation and past experiences in
the form of images are necessary.

C) Affective process – The stimulus in the environment may often have affective component
attached to it. We may like or dislike an object. A stimulus may be pleasant or unpleasant to us. A
stimulus may produce happiness or sadness in us. Or, a stimulus may produce indifferent/neutral
feeling in us.

The basic processes involved in perception make it a complex process. It is not merely an integration
of different sensations. But, even though, it is a complex process, the basic processes are still the
sensation and the past experiences.

Factors influencing perception

Following are the factors that influence perception. These factors can reside in the perceiver, in the object or
target being perceived or in the context of the situation in which perception is made.

1. Factors related to perceiver

a. Motivation
Motives tend to influence perception in the direction of stimuli related to the motive involved like if we
drive down a road while feeling hungry, we probably notice almost every sign of food advertisement.
Sanford, 1936 deprived research participants of food for various length of time up to four hours and
then showed them ambiguous pictures. He found out that the longer the participants had been deprived
of food, more likely they were to interpret the pictures as being something to do with food.

Gilchrist and Nesberb, 1952, asked people to rate pictures for brightness, and found that longer they
had gone without food, brighter the food pictures were rated.

b. Emotion
Following study shows effects of emotion on perception. Soltey and High, 1958, asked children to
draw pictures of Santa Claus in the month leading up the Christmas and month afterwards. The
children’s representation became larger and included more presents as Christmas approached but
shrank and included less detail after the season. This study implied that emotional states such as
anticipation and excitement could also influence perceptual processes.

c. Expectation
In 1955, Bruner and Minturn showed how expectation could influence perception. They began by
showing people either letters or alphabets one at a time. Then they showed them as ambiguous figure
which could be read either as B or 13. The research participants who had seen numbers unequivocally
judged the figure to be as 13 while those who had seen letter previously saw it as B. the gap in the
figure was enlarged by those who believed it to be a 13 but those who believed it to be B did not
include any gap.

A similar study was done by Bugelski and Alampey in 1961 in which the participants in research were
shown either a series of animal pictures or a set of unrelated images like furniture, vehicles, and so on.
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When they were shown an ambiguous batman figure, people were significantly more like a bat than a
man if they had experienced the prior exposure to animal pictures.

d. Culture
Burnes and Goodman have pointed out that cultural groups may differ from one another in their
perceptual behavior because of the fundamental differences in their way of perceiving social situations

e. Attitude
Attitudes do effect perception. In an experiment done by Sheriff and Sheriff in 1956, the perception
was greatly influenced by both inter and intra group attitudes.

2. Factors related to target

a. Size
b. Contrast
c. Repetition
d. Intensity
e. Motion
f. Novelty or familiarity

3. Factors related to situation

a. Time
b. Location
c. Climate
d. State of mind

Perceptual organization

Perceptual organization is the task performed by the perceptual system to determine what edges and other
stimuli go through to form an object (Peterson and Rhodes, 2003)

In early 1990s, there was a debate between structuralist and Gestalt psychologists. Structuralist believed that we
add together hundreds of basic elements to form complex perceptions. But gestalt psychologists believed that
our brain follows a set of rules that specify how individual elements are to be organized into a meaningful
pattern or perception. They believed perceptions do not result from adding sensations. Rather it results from our
brain’s ability to organize sensations according to a set of rules as much as our brain follows a set of rules for
arranging words into sentences.
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1. Figure-ground perception
One of the basic rules in organization is picking out the object from its background. When we look at a
complex scene or listen to a noisy environment, our perceptual apparatus automatically emphasizes certain
features, objects or sounds; all other stimuli in that environment become background. We tend to divide the
world around us into two parts; figure which has a definite shape and location in space and ground which
has no space seems to be continuing behind the figure and has no definite location. In reversible pictures
like the one with an old woman and a young lady, the figure and ground interchange with each other. When
we see young lady, it becomes the figure and the old woman becomes the ground; and when we see the old
woman, it becomes the figure and the young lady becomes the ground.

Considering the reversible figure like Rubin’s face-vase figure, psychologists have studied properties of
figure-ground and they are:
 Figure is more thing like and more memorable than the ground.
 Figure is seen as being in front of the ground
 Ground seems to extend behind the figure.
 Outline separating the figure from the ground appears to belong to the figure.

Following are some of the factors that determine what becomes figure or ground in a picture:
 Lower region of a display tends to be seen as figure.
 Smaller area is more likely to be seen as figure.
 Part of display with meaning is likely to be seen as figure.

2. Principles of grouping/Gestalt’s Laws of grouping

We organize our perception by grouping elements based on the laws as follows:

a. Law of similarity
Similar things appear to be grouped together

In the first pattern of circles, either we perceive them as the horizontal or vertical rows of circles. But in
the second pattern, we perceive it as the vertical column of black circles and white circles. The law of
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similarity causes circles of same color to be grouped together. Similarly, similarity can also occur
because of similarity of shape, size, or orientation.

b. Law of proximity
Things that are near to each other appears to be grouped together. Instead of perceiving as 6 lines, we
perceive it as 3 pairs of lines

c. Law of closure
In organizing stimuli we tend to fill in any missing parts of a figure and see the figure as complete

d. Law of continuity
In organizing stimuli, we tend to favour smooth or continuous paths when interpreting a series of points
or lines

e. Law of simplicity
Stimuli are grouped in the simplest way possible

f. Law of common fate

Elements seen moving together at a same speed at the same direction are perceived as belonging
together
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Errors in perception

1. Illusions
2. Delusions
3. Hallucinations

Illusion

An illusion is a false perception in that it differs from actual physical state of the perceived object (Crooks and
Stein, 1991).

An illusion is a perceptual experience in which we perceive an image or being so strangely distorted that in
reality, it cannot and does not exist. Illusions may be individual or universal. When illusions are limited to
specific person, then it is termed as individual illusion like everyone does not perceive rope as snake in the dark.
On the other hand, there are illusions which are experienced by most of the individuals and such illusions are
called universal illusions.

Illusions that occur because the stimulus contains misleading cues that give rise to inaccurate or impossible
perceptions are called perceptual illusions. Some of the types of illusions are:
a. Muller-lyer illusion (size illusion)

Though both the lines are equal in length, the first line with arrow head appears shorter than the second
line with feather head.

b. Horizontal-vertical illusion (size illusion)

The vertical line always seem longer than the horizontal line though both are same.

c. Ponzo illusion (size illusion)

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Upper and lower of horizontal lines are of same length but upper one appears longer. Converging lines
convey linear perspective, a key to depth cue that makes us perceive the upper line farther in distance
from us. If two lines cast equally long retinal image but one seems farther, the farther one is assumed to
be longer.

d. Moon illusion (shape illusion)

When full moon is near the horizon, it appears as much as 50% larger than when it is high in the sky.
Another theory of moon illusion states that the moon appears smaller when it is surrounded by larger
objects. Thus, when the moon is elevated, the large expanse of sky surroundings makes it appear
smaller. However, when the moon is on the horizon, less sky surrounds it so it appears larger (Braid et.
al., 1990).

e. The Ames room (shape illusion)

The Ames room causes two people of equal size to appear very different in size (Ittleson, 1952). The
reason for this is that the room has a peculiar shape and we look from a fixed peep hole. If we view the
Ames room, from a fixed hole, the room appears rectangular and matches our previous experience with
rooms. However, the Ames room is usually shaped in an odd way that causes the left corner twice as
far away than the right corner.

f. Ebbinghaus illusion/contrast illusion (size illusion)

Two centre circles are of same size but right circle appears to be smaller in comparison to the left
circle.

g. Delbocuf illusion (size illusion)

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The center circles of equal size seem to be smaller in the right picture while the one on left seems
larger.

h. Wundt illusion (size illusion)

Two horizontal lines are both straight but they look as if they are bowed inwards. It is because of
crooked lines on the background.

i. Eherenstein illusion/symmetry illusion (size illusion)

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In this illusion, the sides of a square placed inside a pattern of concentric circles take an apparent curve
shape however the shape is perfect with perfectly straight sides. Angles at which circular lines interact,
the square distort it.

j. Orbison illusion/symmetry illusion (size illusion)

The small circular line seems to be oval egg shaped even though it is perfectly a circle because of the
background.
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k. Sander’s illusion (shape illusion)

l. Poggendorf illusion (shape illusion)

Delusions:
Delusions are irrational beliefs, held with a high level of conviction that are highly resistant to change even
when the delusional person is exposed to forms of proof that contradict the belief.

Following are most common types of delusions

 Grandeur delusion Feeling that he/she is the god.
 Nihilistic delusion Feeling that he/she doesn’t exist in this world and only the soul or ghost is roaming
around that cannot be seen by others.
 Delusion of persecution Feeling that someone is planning against him/her and is trying to kill him/her.
 Delusion of referenceFeeling that someone is watching him/her and talking about him/her i.e. referring
 Hypochondriacal delusion Feeling that he/she has the non-existing disease like blood turning into water,
brain being rotten, etc.
 Self-condemnatory delusion Feeling guilty for whatever is mishappening in this world is because of
him/her

Following are causes of delusions

1. Drug intoxication
2. Dementia
3. Tumour
4. Excess of cortisol
5. Psychotic disorder
6. Injury to brain

Hallucination

Hallucinations are perceptions that occur in a wakeful state and seem real but are created by brain. These
perceptions occur without external stimulation of the relevant sensory organ.

1. Visual hallucination related to eyes and vision. It is seeing things that is not present like god, ghosts,
people who are already dead, etc.

2. Auditory hallucination related to ear and hearing. It is hearing things like voice of god or satan, or
hearing the voice of people from other world.

3. Tactile hallucination feeling of being touched by someone, or hot and cold, etc.

4. Olfactory hallucination sensation of odour i.e. good or bad depending on the mental state of the
individual.

5. Gustatory hallucination Sensation of taste of different things at times without eating anything.

Causes of Hallucination

1. Brain tumor
2. Dementia
3. High fever
4. Sleep deprivation
5. Severe fatigue
6. Consumption of large quantity of alcohol or during withdrawal.