PSY382-HandeKaynak,PhD
2/21/17
Sensation
Chapter 1:
Introduction to Sensation and Perception Perception
•  A mental process
•  The organization,
identification, and
interpretation of sensory
information.
•  A higher brain function
about interpreting events
and objects in the world.
•  is shaped by learning,
memory, expectation, and
attention.
•  A neurophysiological process
•  The detection of the
elementary properties of a
stimulus by a sensory organ.
Sensation and Perception
•  Sensation à detection (there is something
over there)
•  Perception/Recognition à identification
•  Cognition à elaboration
There is something red thereàsensation
That is an appleàperception
That is a rotten appleàcognition
There is no precise borders among these
processes. Unlike, they all depend on
each other. There is a continuity.
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PSY382-HandeKaynak,PhD
2/21/17
Stimuli (Steps 1 and 2)
•  Stimulus
–  Environmental stimulus are all objects in
the environment are available to the
observer.
The perceptual process.
–  Observer selectively attends to objects.
–  Stimulus impinges on receptors resulting in
internal representation.
Figure 1-1 p5
Stimuli (Steps 1 and 2) - continued
•  Principle of transformation
–  Everything a person perceives is based not
on direct contact with stimuli but on
representations of stimuli that are formed
on the receptors and on activity in the
person’s nervous system.
–  distinction between the environmental
stimulus (Step 1) and the stimulus on the
receptors (Step 2). transformation from
“tree” to “image of the tree on the retina”
Figure 1-2 p6
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PSY382-HandeKaynak,PhD
2/21/17
Receptor Processes/Transduction (Step 3)
Receptor Processes/Transduction (Step 3)
–  transduction.
•  The process
–  Sensory receptors are cells specialized to
respond to environmental energy.
•  Visual receptors respond to light, touch
receptors to pressure transmitted through the
skin, and smell and taste receptors to
chemicals entering the nose and mouth.
–  Receptors transform light energy to
electrical energy. This is transduction.
–  Transduction occurs which changes
environmental energy to nerve impulses
–  E.g. touching the “withdrawal” button on an
ATM. The pressure exerted by your finger
is transduced into electrical energy.
•  Transduction is crucial for perception,
because without it, information about the
representation of the tree formed on the
retina would not reach the brain and
perception would not occur.
Neural Processing (Step 4)
•  The process
–  Electrical signals from the receptors, through
the retina, to the brain, and then within the
brain.
–  Electrical signals from each sense arrive at the
primary receiving area.
•  Occipital lobe (for vision)
•  Temporal lobe (for hearing)
•  Parietal lobe (for the skin senses)
The frontal lobe receives signals from all of the senses.
Figure 1-3 p6
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PSY382-HandeKaynak,PhD
2/21/17
Behavioral Responses (Step 5-7)
•  Experience and Action
–  The electrical signals are transformed into
conscious experience. The person
perceives the tree (Step 5) and recognizes
it (Step 6).
–  Perception occurs as a conscious
experience. (conscious awareness of the
tree)
–  Recognition occurs when an object is
placed in a category giving it meaning.
Figure 1-4 p7
Behavioral Responses (Step 5-7)
–  The distinction between Perception and Recognition: the
case of Dr. P., a patient described by neurologist Oliver
Sacks (1985).
Action occurs when the perceiver
initiates motor activity in response to
recognition.
•  Visual form agnosia—an inability to recognize
objects—that was caused by a brain tumor. He
perceived the parts of objects but couldn’t identify
the whole object. When Sacks showed him a
glove, Dr. P. described it as “a continuous surface
unfolded on itself. He could perceive the object
and recognize parts of it, but he couldn’t
recognize the object as a whole.
Figure 1-5 p8
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PSY382-HandeKaynak,PhD
2/21/17
Open your eyes rapidly to briefly expose the picture.
Decide what the picture is!
look at the drawing, then close your eyes.
Figure 1-6 p9
Figure 1-6 p9
Knowledge Did you see a “rat” or a “man”?
Looking at the more ratlike picture increased the
chances that you would see this one as a rat. But if you
had first seen the man version, you would have been
more likely to perceive this figure as a man.
•  Knowledge is any information the perceiver brings to a
situation.
•  This demonstration, which is called the rat–man
demonstration, shows how recently acquired knowledge
(“that pattern is a rat”) can influence perception.
•  Bottom-up processing
–  Processing based on incoming stimuli from the
environment
–  Also called data-based processing
•  Top-down processing
–  Processing based on the perceiver s previous knowledge
(cognitive factors)
Man version of the rat–man stimulus
Figure 1-6 p9
–  Also called knowledge-based processing
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PSY382-HandeKaynak,PhD
2/21/17
Perception is determined by an interaction between bottom-up
processing, which starts with the image on the receptors,
and top-down processing, which brings the observer’s knowledge
into play.
Knowledge The interaction between bottom-up & top-down processing
• E.g. a pharmacist reads what to you might look like an
unreadable scribble on your doctor’s prescription.
• The pharmacist might use her knowledge of the names of
drugs, and perhaps past experience with this particular doctor’s
writing.
• The message is: A person’s past experience is usually involved
in perception of real-world scenes. It is very rare that top-down
processing is probably not involved (involving very simple
stimuli). For example, perceiving a single flash of easily visible
light is probably not affected by a person’s prior experience.
Figure 1-7 p9
What comes to your mind? Simplified perceptual process
Behavioral responses – Step 5-7
Step 3 and 4
Step 1 and 2
Figure 1-8 p10
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PSY382-HandeKaynak,PhD
2/21/17
how well you could see the lines
Approaches to the Study of Perception Perception has been studied using two approaches at
different stages in the system:
1.Psychophysical approach
Psychophysical
(measuring the stimulus-perception relationship.)
(Psychophysics)
The stimulus-perception
relationship
E.g. an experiment in which subjects were tested to see how well they could
see the fine lines in stimuli like the ones in Figure 1.9 that were presented at
different orientations.
Horizontal and vertical lines (stimuli) resulted in better detail vision (the
behavioral response) than slanted lines. This better detail vision for verticals or
horizontals compared to slanted lines is called the oblique effect (Appelle,
1972).
Figure 1-9 p10
Approaches to the Study of Perception Are they similar or different?
2.a.Physiological approach - the stimulusphysiology relationship
2.b.Physiological approach - the
physiology and perception relationship
•  This approach is used to understand the
physiology behind the oblique effect.
•  An example for the stimulus–physiology
relationship for the oblique effect à the
researchers (1998) presented lines with
different orientations to ferrets.
Psychophysical approach
(measuring the stimulus-perception relationship.)
Figure 1-9 p10
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PSY382-HandeKaynak,PhD
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Approaches to the Study of Perception •  An example for the perception–physiology
relationship for the oblique effect à
human subjects’ brain activity was measured in
a brain scanner while they carried out a task
that involved detecting lines with different
orientations (2004).
They used a technique
called optical brain
imaging that
measured activity over
a large area of the
ferret’s visual cortex,
researchers found that
horizontal or vertical
orientations caused
larger brain
responses
(physiological
responses) than
slanted orientations.
Measure the relationship between human
subjects’ brain responses (physiology) and
their ability to judge the orientation of bars
(perception).
Figure 1-11 p11
measuring how a
neuron responds
to different colors
(relationship PH1)
the relationship between human subjects’
brain responses (physiology) and their
ability to judge the orientation of bars
(perception).
or
the relationship
between a person’s
brain activity and that
person’s perception of
colors (relationship
PH2)
Figure 1-12 p11
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PSY382-HandeKaynak,PhD
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Approaches to the Study of Perception continued •  These stages are interconnected and
communicate with one another.
Measuring Perception
•  Absolute threshold - smallest amount of
energy needed to detect a stimulus
–  E.g. 1 tea spoon sugar in 8 lt water (taste)
•  Cognitive influences on perception.
“knowledge” inside the person’s head in the perceptual cycle. E.g. How has knowledge affected the s>mulus–percep>on rela>onship? Like in the rat-­‐man demonstra>on example… –  At night, a candle light away 50 km. (vision)
Measuring Perception
–  Method of limits (Fechner’s classical
psychophysical methods)
Stimuli with different line widths are
presented one at a time, and the subject
indicates the grating’s orientation until the
lines are so close together (the grating will
appear to be a homogeneous
gray field) that the subject can no longer
indicate the orientation.
The threshold is lower (finer
lines can be detected) when
the gratings are horizontal
or vertical rather than
slanted/oblique.
•  Stimuli of different intensities presented
in ascending and descending order
•  Observer responds to whether she
perceived the stimulus
•  Cross-over point is the threshold
Figure 1-13 p12
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PSY382-HandeKaynak,PhD
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an experiment that measures
a person’s threshold for
hearing a tone.
Measuring Thresholds –  Method of adjustment
the experimenter begins
by presenting a tone with
an intensity of 103, and
the observer indicates by
a “yes” response that he
hears the tone.
–  The observer (not the experimenter)
adjusts the stimulus intensity continuously
until he or she can just barely detect the
stimulus.
•  E.g. the observer might be told to turn a knob to
decrease the intensity of a sound until the
sound can no longer be heard.
change from “yes”
to “no,” indicated by the
dashed line, is the
crossover point.
–  This just barely audible intensity is taken as
the threshold.
–  Repeated trials averaged for threshold!
Figure 1-15 p13
Measuring Thresholds - continued
–  Method of constant stimuli
•  Five to nine stimuli of different intensities
are presented in random order.
The threshold for seeing a light is
measured by the method of constant
stimuli. The threshold—the intensity at
which the light is seen on half of its
presentations—is 180 in this experiment.
–  E.g. for seeing a light, intensities of 150, 160, 170,
180, 190, and 200 are presented one at a time. On
each trial, the observer says “yes” or “no” to indicate
whether he or she sees the light.
•  Multiple trials are presented
•  Threshold is the intensity that results in
detection in 50% of trials.
Figure 1-16 p14
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PSY382-HandeKaynak,PhD
Estimating Magnitude 2/21/17
In terms of the brightness of a light, doubling the intensity does
not necessarily double the perceived brightness.
On the other hand, doubling the strength of a shock more than
doubles the perceived magnitude of the shock.
•  How do we measure above-threshold perceptions?
•  Magnitude estimation (scaling)
–  Stimuli are above threshold.
–  Observer is given a ‘standard’ stimulus (like a
light of moderate intensity) and a value for its
intensity (a value of 10).
–  Observer compares the standard stimulus to test
stimuli by assigning numbers relative to the
standard.
•  E.g. If the light appears twice as bright as the standard, it gets a
rating of 20; half as bright, a 5; and so on.
Figure 1-17 p15
Estimating Magnitude - continued
–  Response compression
As intensity increases, the perceived magnitude
increases more slowly than the intensity. (like in
the brightness of a light example)
•  Imagine you are inside reading a book, when you
turn to look out the window at a sidewalk bathed in
intense sunlight. Your eyes may be receiving
thousands of times more light from the sidewalk
than from the page of your book, but because of
response compression, the sidewalk does not
appear thousands of times brighter than the page.
Estimating Magnitude - continued
–  Response expansion
As intensity increases, the perceived magnitude
increases more quickly than the intensity. (like
electric shock)
•  Small increases in shock intensity cause large
increases in pain. This rapid increase in pain
associated with response expansion serves to
warn us of impending danger, and we therefore
tend to withdraw even from weak shocks.
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PSY382-HandeKaynak,PhD
Beyond Thresholds and Magnitudes •  Phenomenological method involves
describe what they are perceiving or to
indicate when a perception occurs.
–  describing the basic properties. For example, a
person might be asked to name the color of a light
or to indicate whether a particular taste is bitter or
sweet.
The phenomenological method is often used when
testing the perception of people with brain damage.
Thus, Dr. P. with visual form agnosia.
2/21/17
Beyond Thresholds and Magnitudes •  Searching for stimuli
–  Visual search - observers look for one stimulus
in a set of many stimuli as quickly as possible.
•  E.g. searching for a friend’s face in a crowd.
sometimes it is easy (if you know your friend is
wearing a bright red hat and no one else is), and
sometimes it is difficult (if there are lots of people and
your friend doesn’t stand out).
•  Reaction time (RT) - time from presentation of
stimulus to observer s response is measured
Threshold Measurements Can Be Influenced
by How a Person Chooses to Respond •  There are differences in response criteria
among participants
–  Liberal responder – responds ‘yes’ if there
is the slightest possibility of experiencing
the stimulus
They picked 5 different
light intensities,
presented them in
random order, and ask
Julie and Regina to say
yes if they see the
light
and no if they don t
see it.
Julie gives many more yes
responses than Regina.
Julie’s threshold is lower than
Regina’s????
Figure 1-18 p16
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PSY382-HandeKaynak,PhD
2/21/17
Threshold Measurements Can Be Influenced
by How a Person Chooses to Respond •  Julie decides that she wants to be sure she doesn’t miss any presenta6ons of the light. She therefore decides to say “yes” if there is even the slightest possibility that she sees the light. •  However, Regina responds more conserva6vely because she wants to be totally sure that she sees the light before saying “yes.” She is not willing to report that she sees the light unless it is clearly visible. •  But is Julie really more sensi6ve to the light than Regina, or does she just appear to be more sensi6ve because she is a more liberal responder? Threshold Measurements Can Be Influenced
by How a Person Chooses to Respond •  Response criterion is a persons individual
response bias.
•  It could be that their actual sensitivity to the
lights is exactly same, but Julie’s response
criterion is low (she says “yes” if there is the
slightest chance a light is present)
•  People may have different response criteria,
so one should take individual’s response
criteria into account.
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