Unit 4. Sensation and
Perception
College Board - “Acorn Book”
Course Description
6-8% (7-9% in past)
Unit IV. Sensaton and
Perception
Overview
 A. Thresholds
 B. Sensory Mechanisms
 C. Attention
 D. Perceptual Processes
Unit IV. Sensaton and
Perception
Unit IV. Sensaton and
Perception
A. Thresholds
 Threshold
 Absolute threshold
 Just-noticeable-difference (jnd)
 Weber’s Law
 Fechner’s Law (Psychophysical scaling)
 Subliminal perception
Unit IV. Sensaton and
Perception
Signal Detection Theory
Chart
Response
Yes
Signal
Present
Signal
Absent
Unit IV. Sensaton and
Perception
Response
No
Signal Detection Theory
Correctly identifies stimulus present
Response
Yes
Signal
Present
Signal
Absent
Unit IV. Sensaton and
Perception
HIT
Response
No
Signal Detection Theory
Fails to identify stimulus present
Signal
Present
Signal
Absent
Unit IV. Sensaton and
Perception
Response
Yes
Response
No
Hit
MISS
Signal Detection Theory
Incorrectly identifies stimulus as present when absent
Unit IV. Sensaton and
Perception
Response
Yes
Response
No
Signal
Present
Hit
Miss
Signal
Absent
FALSE
ALARM
Signal Detection Theory
Correctly identifies stimulus as absent
Unit IV. Sensaton and
Perception
Response
Yes
Response
No
Signal
Present
Hit
Miss
Signal
Absent
False Alarm
Correct
Negative
B. Sensory Mechanisms
 Vision
 The Stimulus – Light

Amplitude, wavelength, purity, saturation
 Structure of the Eye



Unit IV. Sensaton and
Perception
Lens, retina, rods & cones, fovea
Bipolar cells and ganglion cells
Optic nerve and blind spot
Figure 6.7 The eye
Myers: Psychology, Ninth Edition Copyright © 2010 by Worth
Publishers
Figure 6.8 The retina’s reaction to light
Myers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers
Table 6.1
Myers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers
Color - Color - Color
 Chromatic vs. achromatic (Colors vs. black &
white)
 Hue, brightness, saturation (Color, light-dark,
purity of color)
 Subtractive mixture vs. additive mixture
(filters vs. paints)
 Good Web Site on Color Mixing
 http://home.att.net/~RTRUSCIO/COLORSYS.htm
Unit IV. Sensaton and
Perception
Additive
 New colors are made by the combination
of different colored lights
 The three colors used are Red, Green,
and Blue
 This is used for television screens,
video, and computer monitors
Unit IV. Sensaton and
Perception
Source:
http://en.wikipedia.org/wiki/Color_mixing
A simulated
example of
additive
color mixing
Unit IV. Sensaton and
Perception
Subtractive
 New colors can be made when paints,
inks, markers, and other coloring media
are combined
 The three colors used are Magenta,
Yellow, and Cyan
 This is used in color printers
Unit IV. Sensaton and
Perception
Source:
http://en.wikipedia.org/wiki/Color_mixing
A simulated
example of
subtractive
color mixing
Unit IV. Sensaton and
Perception
http://home.att.net/~RTRUSCIO/COLORSYS.htm
 The above site provides an informative
explanation and description of color mixing
 Color Vision
 Mixing Light
 Mixing Dyes – Paints – Ink
 The Basic Three - The physics and biology
of color mixing
 Painting
 Photography
 Printing
 Other Considerations
Unit IV. Sensaton and
Perception
Color Vision
 Trichromactic theory –
 Young-Helmholtz (three color receptors –
different wavelengths)
 Color blindness (dichromats, etc.)
 Processing at receptor level
 Opponent-process theory –
 Hering, Jameson, Hurvich (three pairs of colorsensitive neurons)
 Negative afterimage
 Processing at receptive field level (thalamus)
Unit IV. Sensaton and
Perception
Color Vision:
From Weiten. Themes and Variations. 4th ed. Brooks/Cole. 1998
Unit IV. Sensaton and
Perception
Colors of the Rainbow
R O Y G
B I
V
 Color is determined by wave length
 Red is the longest wavelength of visible
light. Violet is the shortest
 Water (mist) refracts light into different
wavelengths
Unit IV. Sensaton and
Perception
Hearing
 The Stimulus – Soundwaves
 Amplitude (Loudness), Wavelength or
frequency (Pitch), Wave purity or mixture
(Timbre))
 Structure of the Ear
 Outer ear – Auditory canal
 Middle ear – Eardrum, Hammer, Anvil,
Stirrup
 Inner ear – Cochlea, Basilar Membrane
Unit IV. Sensaton and
Perception
The Ear
From Coren, Ward, & Enns. Sensation and Perception 6th ed.
John Wiley & Sons, Inc. 2004
Outer Ear
•Auditory Canal
•Eardrum
Middle Ear
•Hammer, anvil, stirrup
Inner Ear
•Cochlea
Unit IV. Sensaton and
Perception
The Inner Ear
From Coren, Ward, & Enns Sensation and Perception 6th ed. John Wiley &
Sons, Inc. 2004
Unit IV. Sensaton and
Perception
Figure 6.16 Hear here: How we transform sound waves into nerve impulses that our brain
interprets Myers: Psychology, Ninth Edition Copyright © 2010 by Worth Publishers
Taste and Smell
 Taste (Gustatory Sense)
 Stimulus – Chemicals
 Four taste receptors
 Smell (Olfactory Sense)
 Stimulus – Chemicals
 Olfactory bulbs, olfactory cilia
 Pheromones
 Taste and Smell
 Demonstrations
 Raw Apple, Raw Potato, Raw Onion
 Jelly Bellies
Unit IV. Sensaton and
Perception
Skin Senses
 Pressure
 Hot
 Cold
 Pain
 Gate
control theory in pain
perception
Unit IV. Sensaton and
Perception
WHAT IS PAIN?
 Messages about tissue damage are picked up
by nociceptors and transmitted to the spinal
cord via small myelinated fibers and very small
un-myelinated fibers.
 From the spinal cord, the impulses are carried
to the brainstem, thalamus and cerebral cortex,
and ultimately perceived as pain.
 These messages are suppressed by a system
of neurons that orginate in the gray matter of the
midbrain.
Unit IV. Sensaton and
Perception
Unit IV. Sensaton and
Perception
 This descending pathway sends messages to
the spinal cord where it suppresses the
transmission of tissue-damage signals to the
higher brain centers.
 Some of these descending pathways utilize
naturally-occurring chemicals called opioids.
Unit IV. Sensaton and
Perception
Unit IV. Sensaton and
Perception
HOW PAIN KILLERS WORK.
 At the site of injury, the body produces
prostaglandins which increase pain sensitivity.
 Some analgesics, such as aspirin, prevent the
production of prostaglandins.
 Acetaminophen is believed to block pain
impulses in the brain itself.
 Local anesthetics intercept pain signals
traveling up the nerve.
 Opiate drugs prevent the transfer of pain
signals from the spinal cord to the brain.
Unit IV. Sensaton and
Perception
Unit IV. Sensaton and
Perception
Internal Senses
 Kinesthesis
 Internal
body position
 Muscle position
 Vestibular sense
 Balance
 Semi-circular canals in ear
Unit IV. Sensaton and
Perception
C. Sensory Adaptation
 Sensory adaptation is a change in
sensitivity to a stimulus that results
from exposure to the stimulus.
 Examples include adapting to
darkness, adapting to bright
conditions, adapting to hot or cold
conditions, adapting to the
presence of odors, and many more.
Unit IV. Sensaton and
Perception
Sensory Adaptation
 Light and Dark Adaptation
Entering / Exiting a movie theatre
 One eye covered demonstration
 The eye has two types of photorecptors
 Cones (for color)
 Rods (for night vision)

Unit IV. Sensaton and
Perception
Dark Adaptation
 Move into a darkened theater and two
changes occur to increase sensitivity to
light:
 The pupils enlarge. This admits more
light onto the retina of the eye.
 Light-sensitive chemicals in the
photoreceptors increase their
concentration. This makes each
photoreceptor more sensitive to light.
Unit IV. Sensaton and
Perception
Light Adaptation
 Leaving the theater, you encounter
bright light
 Your pupils constrict immediately,
reducing the light reaching the retina
 The light-sensitive chemicals in the
photoreceptors quickly bleach out,
reducing the photoreceptors’
sensitivity to light
Unit IV. Sensaton and
Perception
Preserving Dark Adaptation
 It takes 20-30 minutes to become fully
dark adapted
 This is destroyed by exposure to light in
a few seconds
 Rods are blind to red light
 Cover light source with red lens
Read map with cones
Rods remain dark adapted
Unit IV. Sensaton and
Perception
Sound Adaptation
 Adaptation to loud noise
 Very loud sound


small muscle in the inner ear contracts
dampens sound vibrations being
conducted by the ossicles (bones) to the
chochlea
 Adaptation does not work well for
sudden loud sounds, such as gun shots
Unit IV. Sensaton and
Perception
Odor / Smell
 The sense of smell is probably the
quickest sense - as a whole - to adapt
 We can detect amazingly low
concentrations of some chemicals in the
air (e.g., perfumes) but although the
perfume is still in the air about us, we
quickly cease to detect it
Unit IV. Sensaton and
Perception
Taste
 Certain tastes may cause rather
surprising (and unexpected) anomalies
in other taste stimuli


Eating artichoke makes sour substances
taste sweet briefly
Jujuba temporarily abolishes sweet
sensitivity
 Spicy foods will also stimulate pain
receptors
Unit IV. Sensaton and
Perception
Touch – Heat – Cold
 Skin temperature receptors respond
more to rate of change in temperature
than to steady temperature
 This explains why hot bath feels hot at
first, then cooler
 This explains why pool/ocean feels
freezing at first, then comfortable cool
 Demonstration

Unit IV. Sensaton and
Perception
One Hand in Cold Water, the other in
Warm Water
Pain Adaptation
 Acute pain – tells us to get away from
the painful stimulus
 Chronic pain – tells us not to move
something while it heals
Unit IV. Sensaton and
Perception
C. Attention
 Selective Attention
 Bottleneck Theories of Selective Attention


We have a limited capacity to attend to stimuli
There is no limit to how much stimulation can
be present
 Selective Attention allows us to select what
to attend to


Unit IV. Sensaton and
Perception
Sometimes we seem to do it
Other times it seems to happen to us
Selective Attention and the
Cocktail Party Phenomenon
 Cocktail Party Phenomenon


Unit IV. Sensaton and
Perception
the ability to focus one's listening attention
on a single talker among a mixture of
conversations and background noises,
ignoring other conversations
then if someone over the other side of the
party room calls out our name suddenly,
we also notice that sound and respond to it
immediately
Selective Attention and the
Stroop Test
 Stroop Test




Unit IV. Sensaton and
Perception
Why is this task so difficult to do
reading is an automatic process
color naming is a controlled process
automatic process of reading interferes
with our ability to selectively attend to ink
color
Bottleneck or Filter Models of
Selective Attention
 Early selection
 David Broadbent (1958) proposed that physical




characteristics of messages are used to select one
message for further processing and all others are lost
Attenuation
Treisman (1964) proposed that physical characteristics
are used to select one message for full processing and
other messages are given partial processing
Late Selection
Deutsch & Deutsch (1963) proposed that all messages
get through, but that only one response can be mad
Unit IV. Sensaton and
Perception
D. Perceptual Processes
 Feature analysis
 Bottom-up processing
 Top-down processing
Unit IV. Sensaton and
Perception
Is it a circus act?
 Or a couple dancing?
 Ambiguous or
Reversible figure
 Feature analysis


Unit IV. Sensaton and
Perception
Detecting specific
elements
Assembling them in
a more complex form
Bottom-up
Processing
Recognize
Stimulus
 A progression from

Individual elements to the
whole
Combine features
 Also called data-driven
processing
Detect Specific Features
Unit IV. Sensaton and
Perception
Bottom-Up Processing
 Perception must be largely data-driven
because it must accurately reflect events
in the outside world
 The information is determined mainly be
information from the senses (not from
your expectations)
Unit IV. Sensaton and
Perception
Top-Down
Processing
 A progression from

Form perceptual hypothesis
about the nature of the
stimulus as a whole
The whole to the elements
 Also known as schema-
driven processing
Select and examine
features to
Check hypothesis
Recognize
Stimulus
Unit IV. Sensaton and
Perception
Top-Down Processing
 In many situations your knowledge or
expectations (or schemas) will influence
your perception
 In this case a schema is a pattern
formed earlier in your experiences.
Unit IV. Sensaton and
Perception
 Abstract concepts tend to be referred to as
higher level
 Concrete details are referred to as lower
level
 Top-down occurs when a higher level
concept influences your interpretation of
lower level data
 Set or expectancy demonstrate top-down
processing
 Ambiguous figures often demonstrate topdown processing
Unit IV. Sensaton and
Perception
 Visual Contrast
 Brightness contrast (gray on white
appears darker than gray on black)
 Mach Bands (Series of bands of
increasing darkness - each strip affected
by the neighboring strips)
 Lateral inhibition
Unit IV. Sensaton and
Perception
Brightness Contrast
Unit IV. Sensaton and
Perception
Principles of Perceptual
Organization:
 Figure-Ground
 Grouping (Gestalt Principles)




Unit IV. Sensaton and
Perception
Proximity (Nearness)
Similarity
Continuity
Closure
Closure
Unit IV. Sensaton and
Perception
 Perception of Depth and Distance
 Perception of Motion
 Perceptual Constancy (Size, Shape,
Brightness)
 Perceptual Illusions
 Perceptual Set
 Perceptual Adaptation
Unit IV. Sensaton and
Perception
Depth Perception
 “I could have
sworn that
mesa was a
whole lot
farther away”
Unit IV. Sensaton and
Perception
Necker cube (1)
Unit IV. Sensaton and
Perception
Necker cube (2)
Unit IV. Sensaton and
Perception
Necker cube (3)
Unit IV. Sensaton and
Perception
Necker cube (4)
Unit IV. Sensaton and
Perception
Necker cube (5)
Unit IV. Sensaton and
Perception
Handouts
 DISTRIBUTION OF RODS AND CONES
– Bernstein (Colored pencils)
 Light-Dark Sensory Adaptation
Demonstration (Eyepatch)
 Simple Compelling Demonstrations of
Retinal Disparity (“Hole in hand” etc.)
 DEMONSTRATING THAT SMELL IS AS
IMPORTANT – Beins (Jelly Bellies)
Unit IV. Sensaton and
Perception
 Monocular Depth Perception Student
Assignment
 Chart - Depth Perception Cues (Study
Guide / May be used in a variety of
assignments)
 Color Vision – Roygbiv (Demonstration)
 Pulfrich effect (Reading from Wikipedia)
Unit IV. Sensaton and
Perception
 Moon Illusion (Reading from Bad
Astronomy by Philip Plait)
 The Big Picture - Gestalt applied
 The Neuroscience of Yorick's Ghost and
Other Afterimages
 Mindsights Tables (Drawing by Shepard)
 Various Visual Illusions
Unit IV. Sensaton and
Perception
The Janus Mask
The Magic of the Wundt-Jastrow
Illusion
From: Gregory, R. I., Eye and Brain (2nd ed.) New York:
World University Library, 1973. (pp. 78-80.)