Sensation and Perception
Chapter 3
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Sensation vs. Perception

Sensation


The experience of sensory stimulation
Perception

The process of creating meaningful patterns
from raw sensory information
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Nature of Sensation
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Basic Process

Receptor cells


Specialized cells that respond to a particular
type of energy
Doctrine of specific nerve energies
One-to-one relationship between stimulation
of a specific nerve and the resulting sensory
experience
 For example, applying pressure with your
finger to your eye results in a visual
experience

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Sensory Thresholds

Absolute threshold

The minimum amount of energy that can be
detected 50% of the time
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Absolute Thresholds





Taste: 1 gram (.0356 ounce) of table salt in 500
liters (529 quarts) of water
Smell: 1 drop of perfume diffused throughout a
three-room apartment
Touch: the wing of a bee falling on your cheek
from a height of 1cm (.39 inch)
Hearing: the tick of a watch from 6 meters (20
feet) in very quiet conditions
Vision: a candle flame seen from 50km (30
miles) on a clear, dark night
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Sensory Thresholds

Sensory adaptation


An adjustment of the senses to the level of
stimulation they are receiving
Difference threshold
The smallest change in stimulation that can
be detected 50% of the time
 Also called the just noticeable difference

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Sensory Thresholds

Weber’s Law
States that the difference threshold is a
constant proportion of the specific stimulus
 Senses vary in their sensitivity to changes in
stimulation

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Subliminal Perception
The notion that we may respond to stimuli
that are below our level of awareness
 Research shows that the effect only
occurs in controlled laboratory studies
 Research outside the laboratory shows no
significant effect of subliminal information

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Extrasensory Perception

Refers to extraordinary perception such as
Clairvoyance – awareness of an unknown
object or event
 Telepathy – knowledge of someone else’s
thoughts or feelings
 Precognition – foreknowledge of future events


Research has been unable to conclusively
demonstrate the existence of ESP
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Vision
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Visual System

Cornea


Pupil


Transparent protective
coating over the front
of the eye
Small opening in the
iris through which light
enters the eye
Iris

Colored part of the eye
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Visual System

Lens


Retina


Focuses light onto the
retina
Lining of the eye
containing receptor
cells that are sensitive
to light
Fovea

Center of the visual
field
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Receptor Cells
Cells in the retina that are sensitive to light
 Visual receptors are called rods and cones

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Receptor Cells

Rods





About 120 million rods
Respond to light and
dark
Very sensitive to light
Provide our night
vision
Cones




About 8 million cones
Respond to color as
well as light and dark
Work best in bright
light
Found mainly in the
fovea
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Receptor Cells

Bipolar cells


Ganglion cells


Receive input from
receptor cells
Receive input from
bipolar cells
Blind spot

Area where axons of
ganglion cells leave
the eye
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Adaptation

Dark adaptation


Light adaptation


Increased sensitivity of rods and cones in
darkness
Decreased sensitivity of rods and cones in
bright light
Afterimage

Sense experience that occurs after a visual
stimulus has been removed
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
From Eye to Brain

Optic nerve



Made up of axons of
ganglion cells
carries neural
messages from each
eye to brain
Optic chiasm

Point where part of
each optic nerve
crosses to the other
side of the brain
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Color Vision

Properties of color
Hue – refers to colors such as red and green
 Saturation – refers to the vividness of a hue
 Brightness – the nearness of a color to white

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Theories of Color Vision

Additive color mixing
Mixing of lights of different hues
 Lights, T.V., computer monitors (RGB)


Subtractive color mixing

Mixing pigments, e.g., paints
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Theories of Color Vision

Trichromatic theory

Three different types of cones
 Red
 Green
 Blue-violet
Experience of color is the result of mixing of
the signals from these receptors
 Can account for some types of colorblindness

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Forms of Colorblindness


Approximately 10% of
men and 1% of women
have some form of
colorblindness
Dichromats


People who are blind to
either red-green or blueyellow
Monochromats

People who see no color at
all, only shades of light and
dark
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Theories of Color Vision

Trichromatic theory cannot explain all
aspects of color vision
People with normal vision cannot see
“reddish-green” or “yellowish-blue”
 Color afterimages

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Theories of Color Vision

Opponent-process theory

Three pairs of color receptors
 Yellow-blue
 Red-green
 Black-white
Members of each pair work in opposition
 Can explain color afterimages


Both theories of color vision are valid
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Color Vision in Other Species
Other species see colors differently than
humans
 Most other mammals are dichromats
 Rodents tend to be monochromats, as are
owls who have only rods
 Bees can see ultraviolet light

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Hearing
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Sound

Sound waves


Changes in pressure
caused by molecules
of air moving
Frequency


Number of cycles per
second in a wave,
measured in Hertz
(Hz)
Frequency determines
pitch
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Sound

Amplitude



Overtones


Magnitude (height) of
sound wave
Determines loudness,
measured in decibels (dB)
Multiples of the basic tone
Timbre

Quality of texture of sound
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Ear


Eardrum
Middle ear


Contains three small
bones; the hammer,
anvil, and stirrup
These bones relay and
amplify the incoming
sound waves
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Ear

Oval window


Membrane between
middle ear and inner
ear
Cochlea


Part of inner ear
containing fluid that
vibrates
This causes the
basilar membrane to
vibrate
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Ear

Basilar membrane


Membrane in the
cochlea which
contains receptor
cells, called hair cells
Auditory nerve


Connection from ear to
brain
Provides information
to both sides of brain
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Theories of Hearing

Place theory


Frequency theory


Pitch is determined by location of vibration
along the basilar membrane
Pitch is determined by frequency hair cells
produce action potentials
Volley Principle

Pattern of sequential firing determines pitch
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Hearing Disorders
About 28 million people have some form of
hearing damage in the U.S.
 Can be caused by

Injury
 Infections
 Explosions
 Long-term exposure to loud noises

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Other Senses
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Smell

Detecting common odors



Odorant binding protein is
released and attached to
incoming molecules
These molecules then
activate receptors in the
olfactory epithelium
Axons from those receptors
project directly to the
olfactory bulb
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Smell
Women have a better sense of smell than
men
 Anosmia


Complete loss of the ability to smell
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Smell

Pheromones





Used by animals as a form of communication
Provides information about identity
Also provides information about sexual receptivity
Pheromones stimulate the vomeronasal organ
(VNO)
Information from the VNO is sent to a special
part of the olfactory bulb used for pheromonal
communication
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Taste

Four basic tastes
Sweet
 Salty
 Sour
 Bitter


Recent discovery of fifth taste

Umami
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Taste



Receptor cells are
located in taste buds
Taste buds are
located in papillae on
the tongue
Chemicals dissolve in
saliva and activate
receptors
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Other Senses
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Kinesthetic Senses

Kinesthetic senses provide information
about speed and direction of movement
Stretch receptors sense muscle stretch and
contraction
 Golgi tendon organs sense movement of
tendons

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Vestibular Senses
Vestibular senses provide information
about equilibrium and body position
 Fluid moves in two vestibular sacs
 Vestibular organs are also responsible for
motion sickness
 Motion sickness may be caused by
discrepancies between visual information
and vestibular sensation

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
The Skin Senses
Skin is the largest sense organ
 There are receptors for pressure,
temperature, and pain
 Touch appears to be important not just as
a source of information, but as a way to
bond with others

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Pain
Serves as a warning about injury or other
problem
 Large individual differences in pain
perception
 Gate control theory


Neurological “gate” in spinal cord which
controls transmission of pain to brain
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Pain

Biopsychosocial theory


Holds that pain involves not just physical stimulus, but
psychological and social factors as well
Placebo effect


Shows that when a person believes a medication
reduces pain, their pain is often reduced even though
no medication was given
Pain relief is likely the result of endorphin release
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Pain

Alternative approaches
Hypnosis
 Self-hypnosis
 Accupuncture

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Perception
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Perceptual Organization

Figure-ground


We perceive a
foreground object
(figure) against a
background (ground)
Animals may look like
the background they
inhabit as a way of
destroying figureground distinction
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Perceptual Organization

Other principles of
organization




Proximity
Similarity
Closure
Continuity
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Perceptual Organization

Perceptual Constancy





Our tendency to
perceive objects as
stable and unchanging
despite changing
sensory information
Size constancy
Shape constancy
Brightness constancy
Color constancy
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Perception of Distance and
Depth

Monocular cues –
those that require
only one eye





Aerial perspective
Texture gradient
Linear perspective
Motion parallax
Superposition
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Perception of Distance and Depth

Binocular cues – those that require both
eyes
Retinal disparity
 Convergence

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Localizing Sounds


We use both monaural
and binaural cues
Loudness


Louder sounds are
perceived as being closer
Time of arrival


Sounds will arrive at one
ear sooner than the other
This helps determine
direction of the sound
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Perception of Movement

Apparent movement


Autokinetic illusion


Perceived motion of a single object
Stroboscopic motion


Illusion that still objects are moving
Created by a rapid series of still pictures
Phi phenomenon

Apparent motion created by lights flashing in
sequence
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Visual Illusions


Occur because of
misleading cues in
the stimulus
Gives rise to false
perceptions
Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall
Individual Differences and
Culture in Perception

Motivation

Our desires or needs shape our current
perceptions
Values
 Expectations
 Cognitive Style
 Experience and Culture
 Personality

Psychology: An Introduction
Charles A. Morris & Albert A. Maisto
© 2005 Prentice Hall