chapter 6
Sensation and Perception
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Overview
Our sensational senses
Vision
Hearing
Other senses
Perceptual powers
Puzzles of perception
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Definitions
Sensation
The detection of physical energy emitted or reflected by
physical objects
Occurs when energy in the external environment or the
body stimulates receptors in the sense organs
Perception
The process by which the brain organizes and interprets
sensory information
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Ambiguous figure
Colored surface can
be either the outside
front surface or the
inside back surface.
But not simultaneously both
The brain can
interpret the
ambiguous cues in
two different ways.
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Riddle of separate
sensations
Sense
receptors
Specialized cells that
convert physical
energy into electrical
energy that can be
transmitted as nerve
impulses to the brain
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Sensation and perception
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Specific nerve energies
Different sensory modalities exist
because signals received by the sense
organs stimulate different nerve
pathways leading to different areas of
the brain.
Synesthesia
A condition in which stimulation of one sense also
evokes another
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Absolute threshold
The smallest quantity of physical
energy that can be reliably
detected by an observer
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Absolute thresholds
Vision
A single candle flame from 30 miles on a clear night
Hearing
The tick of a watch from 20 feet in total quiet
Smell
One drop of perfume in a 6-room apartment
Touch
The wing of a bee on the cheek, dropped from 1 cm
Taste
One teaspoon of sugar in 2 gallons of water
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Difference threshold
The smallest difference in stimulation
that can be reliably detected by an
observer when two stimuli are
compared
Also called the Just Noticeable
Difference (JND)
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Signal-detection theory
A psychophysical theory that divides the
detection of a sensory signal into a
sensory process and a decision process
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Sensory adaptation and
deprivation
Adaptation
The reduction or disappearance of sensory
responsiveness when stimulation is unchanging or
repetitious
Prevents us from having to respond continuously to
unimportant information
Deprivation
The absence of normal levels of sensory stimulation
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Sensory overload
Over-stimulation of the senses
Can use selective attention to reduce
sensory overload
Selective attention: the focusing of
attention on selected aspects of the
environment and the blocking out of others
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Vision
What we see
An eye on the world
Why the visual system is not a camera
How we see colors
Constructing the visual world
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What we see
Hue
Visual experience specified by color names and related
to the wavelength of light
Brightness
Visual experience related to the amount of light emitted
from or reflected by an object
Saturation
Visual experience related to the complexity of light
waves
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What we see
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An eye on the world
Cornea
Protects eye and bends light
toward lens
Lens
Focuses on objects by changing
shape
Iris
Controls amount of light that gets
into eye
Pupil
Aperture through which light
reaches the retina
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An eye on the world
Retina
Neural tissue lining the back
of the eyeball’s interior
containing the receptors for
vision
Rods
Visual receptors that respond
to dim light
Cones
Visual receptors involved in
color vision
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Structures of the retina
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Your turn
You have a hard time locating your red car at
night, in the poorly lit mall parking lot. Why?
1. Your rods are less sensitive to color in dim light.
2. Your cones, which detect color, do not function well in dim
light.
3. Your ganglion cells receive insufficient overall stimulation to
function.
4. Your rods, which detect color, do not function well in dim light.
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Your turn
You have a hard time locating your red car at
night, in the poorly lit mall parking lot. Why?
1. Your rods are less sensitive to color in dim light.
2. Your cones, which detect color, do not function well in
dim light.
3. Your ganglion cells receive insufficient overall stimulation to
function.
4. Your rods, which detect color, do not function well in dim light.
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The visual system is not
a camera
Much visual processing is done in the
brain
Some cortical cells respond to lines in specific orientations
(e.g., horizontal).
Other cortical cells respond to other shapes (e.g., bullseyes, spirals, faces).
Feature detectors
Cells in the visual cortex that are sensitive to specific
features of the environment
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Huble and Wiesel’s
experiment
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Trichromatic theory
Young (1802) and
von Helmholtz (1852)
both proposed that
the eye detects 3
primary colors
Red, blue, and green
All other colors
derived by
combination
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Opponent-process
theory
A competing theory of color vision,
which assumes that the visual system
treats pairs of colors as opposing or
antagonistic
Opponent-process cells are inhibited
by a color, and have a burst of activity
when it is removed.
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Form perception
Gestalt principles describe the brain’s
organization of sensory building blocks into
meaningful units and patterns.
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Gestalt principles
Proximity
Things close to one another are grouped together
Closure
The brain tends to fill in gaps to perceive complete forms
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Gestalt principles
Similarity
Things that are alike are perceived together
Continuity
Seeing continuity in lines that could be interpreted as either
continuous or abruptly shifting in direction.
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Your turn
Which Gestalt
principle is illustrated
by the fact that we
see columns of dots
rather than rows in
this diagram?
1.
2.
3.
4.
Similarity
Proximity
Closure
Continuity
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Your turn
Which Gestalt
principle is illustrated
by the fact that we
see columns of dots
rather than rows in
this diagram?
1.
2.
3.
4.
Similarity
Proximity
Closure
Continuity
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Depth and distance
perception
Binocular cues: visual cues that require
the use of both eyes
Convergence
Turning inward of the eyes, which occurs when they focus
on a nearby object
Retinal disparity
The slight difference in lateral separation between two
objects as seen by the right and left eyes
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Depth and distance
perception
Monocular cues: visual cues that can be
used by one eye
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Visual constancies
The accurate perception of objects as
stable or unchanged despite changes
in the sensory patterns they produce
Shape constancy
Location constancy
Size constancy
Brightness constancy
Color constancy
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The Müller-Lyer illusion
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Fooling the eye
The cats in (a) are the same size.
The diagonal lines in (b) are parallel.
You can create a “floating fingertip frankfurter” by
holding hands as shown, 5–10 inches in front of face.
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What we hear
Loudness
The dimension of auditory experience related to the intensity of a
pressure wave
Pitch
The dimension of auditory experience related to the frequency of a
pressure wave
Timbre
The dimension of auditory experience related to the complexity of
a pressure wave
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An ear on the world
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Auditory localization
Sounds from different
directions are not
identical as they arrive at
left and right ears.
Loudness
Timing
Phase
The brain calculates a
sound’s location by using
these differences.
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Other senses
Taste: savory sensations
Smell: the sense of scents
Senses of the skin
The mystery of pain
The environment within
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Taste: savory sensations
Taste buds
Nests of taste-receptor cells
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Five tastes
Five basic tastes
Salty, sour, bitter, sweet, umami
Different people have different tastes
based on:
Genetics
Culture
Learning
Food attractiveness
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Smell: the sense of scents
Airborne chemical molecules enter the nose
and circulate through the nasal cavity.
Vapors can also enter through the mouth and pass into nasal
cavity.
Receptors on the roof of the nasal cavity
detect these molecules.
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Sensitivity to touch
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Gate-control theory of
pain
Experience of pain
depends in part on
whether the pain
gets past a
neurological
“gate” in the
spinal cord.
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Gate-control theory revised
The matrix of
neurons in the
brain is capable of
generating pain
(and other
sensations) in the
absence of signals
from sensory
nerves.
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The environment within
Kinesthesis
The sense of body position and movement of body parts
Equilibrium
The sense of balance
Semicircular canals
Sense organs in the inner ear, which contribute to
equilibrium by responding to rotation of the head
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The visual cliff
Glass surface, with
checkerboard underneath
at different heights
Visual illusion of a cliff
Baby can’t fall
Mom stands across the
gap.
Babies show increased
attention over deep side at
age 2 months, but aren’t
afraid until about the age
they can crawl.
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Critical period
If infants miss out on
experiences during a
crucial period of time,
perception will be
impaired.
When adults who have
been blind since birth have
vision restored, they may
not see well.
Other senses such as
hearing may be influenced
similarly.
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Psychological and cultural
influences
We are more likely to perceive something when we
need it.
What we believe can affect what we perceive.
Emotions, such as fear, can influence perceptions of
sensory information.
Expectations based on previous experiences can
influence perception.
Perceptual set: a habitual way of perceiving, based on
expectations
All are influenced by culture.
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Perception vs. persuasion
Although subliminal priming can influence
judgments and preferences, research
doesn’t support its success in major levels
of persuasion.
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Extrasensory perception
The ability to perceive something without
ordinary sensory information
Has not been scientifically demonstrated