PharmD Program / Fourth Year
SENSATIONS AND PERCEPTIONS
Dr. Souada Elhdere
PharmD Faculty of Pharmacy/ Libyan International Medical University
Intended learning outcomes
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By the end of this session you will be able to:
1- Distinguish between sensation and perception;
2- Outline some factors which determine perception.
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Introduction
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Today we will focus on the field of psychology concerned with the
nature of information obtained through the senses and the way in
which we interpret such information. Information from the three-
dimensional real world is received through our senses in two
dimensions and processed to provide a basis for our interaction
with the environment.
The interpretation of this information within the brain results in
three-dimensional perception. This perception of depth depends
on the brain’s use of a number of clues.
Sensation and perception are an important topics. Because our
behavior is so much a reflection of how we react to and interpret
stimuli from the world around us.
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Simple and complex questions related with our day
to day experiences such as:
What processes enable us to see and hear?
How we know whether sugar or lemon is sweeter?
How we distinguish one person from another?
We can get answers to the above questions from our
knowledge of sensation and perception.
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Sensation and perception are the starting
points for all other psychological processes.
They supply the data we use for learning and
remembering for thinking and problem solving,
for communicating with others, for experiencing
emotions, and for being aware of ourselves.
Without sensation and perception we would
not form thoughts or feelings.
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Brain storming activity: read the following
case and brainstorm the questions below it.
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Nada is at her parent’s home for the Eid vacation. It is a
semester break. She is exhausted from campus life,
intensive academic work and especially from the
tasteless lunches at the campus cafeteria. But these
thoughts were soon interrupted when she saw her
mother carrying rice with asban (one of her favorite
dishes), on a tray and placed it at the center of the table.
All family members were sitting and they were talking
and laughing.. The smell of the asban reached Nada and
soon she felt her stomach growl from hunger. The sight
and voice of her family members around the table along
with the smell and taste of the asban made Nada feel
more comfortable and forget the tiresome college life.
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Brainstorming questions
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How different her feeling be if any one of
Nada’s senses were not functioning?
What would happen to Nada had she not
listened to the conversion of her family
members?
What would happen to Nada had she not feel
her stomach growl or smell the dinner, or
taste the food?
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Basic terms and concepts related to
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sensation and perception
To have a better understanding of the subject matter of
sensation and perception, we need to define related
basic terms.
1- Stimulus:
It is a source of physical energy that produces a response
in the sense organs. The energy could be sound waves,
light waves, and heat pressure to which an organism is
capable of responding. A sensation is a response to that
energy by a sensory system. Stimulus and sensation have
cause and effect relationship.
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The quality of a stimulus refers to the kind of
sensation it produces.
Example: Color----- visual stimulation
Musical pitch------auditory stimulation
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The quantity of a stimulus refers to the amount
of stimulus present.
Example: brightness, loudness
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Stimuli vary in both type and intensity. Different types
of stimuli activate different sense organs.
Example: A light stimulus that activates our sense of
sight and allows us to see the color of a tree is called
type. A sound stimulus that permits us to hear the
sound of a musical instrument is called type.
How high a light stimulus needs to be before it is
capable of being detected is intensity. How much
perfume a person must put on before others notice it
is termed as intensity.
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2. Response:
It is any reaction of an organism to or in the presence
of a stimulus. The reaction could be muscular or
glandular.
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3. Sensation
It is the process by which an organism’s sense
organs respond to a stimulus. It is the process
whereby stimulation of receptor cells (in the
eyes, ears, nose, mouth, and surface of the skin)
sends nerve impulses to the brain. After
reaching the brain they are registered as a
touch, a sound, a taste, and a splash of color.
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4.Transduction:
It is the sequence of operation by which
physical energy (example, sound waves, light) is
transformed into patterns of neural impulse
that give rise to sensory experience.
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5. Perception:
It is the process whereby the brain interprets
sensations, giving information order and meaning.
It takes into account experiences stored in our
memory, the context in which the sensation occurs
and our internal state (our emotions and
motivations). It is the process of forming hypotheses
about what the senses tell us.
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Example: Hearing sounds and seeing colors are
sensory processes; whereas, listening sweet
music and detecting depth in a two dimensional
picture are perceptual processes. Without
sensation of some kind perception could not
occur.
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factors that affect our perception
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There are several factors that affect our perception. Some of these are:
a. Context and expectation
In an experiment by Bruner and Minturn (1955, cited by Baron),
participants were shown sequences either of letters or of numbers,
for example:
C D E F G H or
8 9 10 11 12
When perceived with a figure/number I3 that could be either B or 13, those
who had seen the sequence or letters tended to perceive it as B, while those
who had seen the numbers perceived it as 13.
The context in which it was seen produced expectation and induced a
particular set.
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b. Motivation
Studies have shown the effects of motivation upon
the way in which things are perceived. Solley and
Haigh(1956, cited in Baron), for instance, asked
children aged four to eight to draw pictures of Santa
Claus during the month running up to Christmas. As
Christmas approached, Santa Claus became larger,
nearer, more elaborate, a more decorated costume
and a bigger bag of presents. After Christmas, Santa
shrank and his present bag all but disappeared.
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c. Emotion and perception
In a study by McGinnis (1949, cited in Baron),
participants were presented with either neutral
stimulus such as table apple chair or ‘taboo’ words.
Each of these words was presented very briefly, then
for increasing length of time. At the same time a
measure of emotional response (Galvanic Skin
Response) was taken. It was found that the taboo
words had a higher recognition threshold and were
also accompanied by greater GSR.
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d. Values, culture and personality
There is evidence that suggests that an individual’s
value system may induce a set. Post man (1948,cited in
Baron), rated participants on the Allport-Vernnon scale
of values. The scale divides values into six categories.
These are theoretical, social, economic, aesthetic,
political and religious. The result showed that, words,
which are related to highly rated value categories,
were found to be more easily perceived than lower-
rated values. Cultural prejudices have an effect upon
perception. 19/11/2019
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6. Absolute threshold:
It is the smallest intensity of a stimulus that
must be present for it to be detected. For a
stimulus to be detected by our sense organs it
must become strong enough.
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The following research findings on absolute threshold are taken
from the works of Galanter (1962) as cited in (Feldman, 1996)
Sight: a candle flame can be seen 30 miles away on a
dark, clear night.
Hearing: the ticking of a watch can be heard 20 feet away
under quiet conditions.
Taste: A teaspoon of sugar can be detected in nine liters
of water
Smell: A drop of perfume can be detected when one drop
is present in a three-room apartment.
Touch: The falling of a bee’s wing from a distance of one
centimeter can be felt on a cheek.
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7. Difference threshold:
it is the smallest detectable difference between two
stimuli. A noticeable difference depends on the
value of the initial intensity of the stimulus.
Example: When the moon is seen in the late
afternoon, it appears relatively dim. When it is seen
in the dark, it seems quite bright.
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8. Sensory adaptation:
It is an adjustment in sensory capacity following
long period of exposure to stimuli. It is the
tendency of receptor cells in the sense organs
to respond less and less to a constant stimulus.
Adaptation occurs as a result of prolonged
exposure to stimuli, a change in the attitude
and expectation of the individual.
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Example: Repeated hearing of a musical sound in a
bar makes a person to adjust as if it were softer.
When you enter into the dormitory with a distinct
odor, the smell is very noticeable at first, but soon it
seems to fade.
One explanation for decline in sensitivity to sensory
stimuli is the inability of the sensory nerve receptors
to constantly carry messages to the brain. They stop
reacting to constant stimulation.
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The sense of smell and touch adapt quickly.
Pain adaptation is slower. However, sensory
adaptation occurs with all the senses.
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9. Attention:
Attention is a general term referring to the selective
aspects of perception which function so that any instant
an organism focuses on certain features of the
environment to the exclusion of other features.
A factor of importance in the study of perception is
attention. Human beings are constantly encountered
with stimuli from the environment in which they live; but
they use only a very small portion of this information.
Selective attention enables them to sort out and process
this information.
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Factors which determine whether or not we pay
attention to a stimulus are:
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1. Intensity: a bright color will attract us more than a dull one.
2. Size: a large thing is more likely to catch our attention than
something small.
3. Duration of repetition: a quickly running stimulus will not
catch our attention as easily as one, which persists or is repeated.
4. Emotional content: a stimulus, which creates emotional
feeling, attracts our attention more than a neutral one.
5. Suddenness : sudden stimulus is likely to catch
our attention more easily than one we have been expecting.
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Summary
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We distinguished between sensation and perception;
and we defined Basic terms and concepts related to
sensation and perception, These terms are ( stimulus,
response , sensation, transduction, perception,
absolute threshold, difference threshold, sensory
adaption, attention).
We defined factors affect our perception, these factors
are ( content and expectation, motivation, emotion
and perception, values culture and personality).
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