Sensation and Perception
Chapter 6
Our Sensational Senses
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Defining sensation and perception
The riddle of separate senses
Measuring the senses
Sensory adaptation
Sensory overload
Defining Sensation and Perception
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Sensation
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The detection of physical energy emitted or
reflected by physical objects.
It occurs when energy in the external
environment or the body stimulates receptors
in the sense organs.
Perception
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The process by which the brain organizes and
interprets sensory information.
Ambiguous Figure
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Colored surface can
be either the outside
front surface or the
inside back surface
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Cannot
simultaneously be
both
Brain can interpret
the ambiguous cues
two different ways
The Riddle of Separate Sensations
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Sense receptors
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Specialized cells that
convert physical
energy in the
environment or the
body to electrical
energy that can be
transmitted as nerve
impulses to the
brain.
Sensation & Perception Processes
Doctrine of Specific Nerve Energies
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Different sensory modalities exist because
signals received by the sense organs
stimulate different nerve pathways leading
to different areas of the brain.
Synthesia
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A condition in which stimulation of one sense
also evokes another.
Measuring Senses
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Absolute threshold
Difference threshold
Signal-detection theory
Absolute Threshold
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The smallest quantity of physical energy that can
be reliably detected by an observer.
Absolute Sensory Thresholds
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Vision:
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Hearing:
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1 drop of perfume in a 6-room apartment
Touch:
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The tick of a watch from 20 feet in total quiet
Smell:
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A single candle flame from 30 miles on a dark, clear
night
The wing of a bee on your cheek, dropped from 1 cm
Taste:
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1 tsp. Sugar in 2 gal. water
Difference Threshold
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The smallest difference in stimulation that
can be reliably detected by an observer
when two stimuli are compared;
Also called Just Noticeable Difference
(JND).
Signal-Detection Theory
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A psychophysical theory that divides the detection of
a sensory signal into a sensory process and a decision
process.
Stimulus is
Present
Response: Hit
“Present”
Response: Miss
“Absent”
Stimulus is
Absent
False Alarm
Correct
Rejection
Sensory Adaptation and Deprivation
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Adaptation
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The reduction or disappearance of sensory
responsiveness when stimulation is
unchanging or repetitious.
Prevents us from having to continuously
respond to unimportant information.
Deprivation
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The absence of normal levels of sensory
stimulation.
Sensory Overload
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Overstimulation of the senses.
Can use selective attention to reduce
sensory overload.
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Selective attention
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The focusing of attention on selected aspects of
the environment and the blocking out of others.
Vision
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What we see
An eye on the world
Why the visual system is not a camera
How we see colours
Constructing the visual world
What We See
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Hue
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Brightness
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Visual experience specified by colour names
and related to the wavelength of light.
Lightness and luminance; the visual experience
related to the amount of light emitted from or
reflected by an object.
Saturation
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Vividness or purity of colour; the visual
experience related to the complexity of light
waves.
What We See
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Hue
Brightness
Saturation
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Cornea
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Lens
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Focuses on objects by
changing shape.
Iris
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Protects eye and bends
light toward lens.
Controls amount of light
that gets into eye.
Pupil
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Widens or dilates to let
in more light.
An Eye on the World
An Eye on the World
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Retina
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Rods
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Neural tissue lining the back of the eyeball’s
interior, which contains the receptors for vision.
Visual receptors that respond to dim light.
Cones
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Visual receptors involved in colour vision. Most
humans have 3 types of cones.
The Structures of the Retina
Why the Visual System is not a Camera
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Much visual processing is done in the
brain.
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Some cortical cells respond to lines in
specific orientations (e.g. horizontal).
Other cells in the cortex respond to other
shapes (e.g., bulls-eyes, spirals, faces).
Feature-detectors
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Cells in the visual cortex that are sensitive to
specific features of the environment.
Hubel & Wiesel’s Experiment
How We See Colours
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Trichromatic theory
Opponent process theory
Trichromatic Theory
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Young (1802) & von
Helmholtz (1852)
both proposed that the
eye detects 3 primary
colours:
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red, blue, & green
All other colours can
be derived by
combining these
three.
Opponent-Process Theory
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A competing theory of
colour vision, which
assumes that the visual
system treats pairs of
colours as opposing or
antagonistic.
Opponent-Process
cells are inhibited by a
colour, and have a
burst of activity when
it is removed.
Afterimages
Test of Colour Deficiency
Constructing the Visual World
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Form perception
Depth and distance perception
Visual constancies: When seeing is
believing
Visual illusions: When seeing is misleading
Form Perception
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Gestalt principles describe the brain’s
organization of sensory building blocks
into meaningful units and patterns.
Figure and Ground
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Proximity
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Similarity
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Seeing columns of
orange and red dots in
B.
Continuity
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Seeing 3 pair of lines in
A.
Seeing lines that connect
1 to 2 and 3 to 4 in C.
Closure
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Seeing a horse in D.
Depth and Distance Perception
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Binocular Cues:
Visual cues to depth or distance 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 left eye and the right eye.
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Depth and Distance Perception
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Monocular Cues:
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Visual cues to depth or distance that can be
used by one eye alone.
The Ames Room
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A specially-built room
that makes people seem
to change size as they
move around in it
The room is not a
rectangle, as viewers
assume it is
A single peephole
prevents using binocular
depth cues
Visual Constancies
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The accurate perception of objects as stable
or unchanged despite changes in the
sensory patterns they produce.
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Shape constancy
Location constancy
Size constancy
Brightness constancy
Colour constancy
Shape Constancy
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Even though these images cast shadows of
different shapes, we still see the quarter as round
Visual
Illusions
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Illusions are valuable in understanding perception
because they are systematic errors.
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Illusions provide hints about perceptual strategies.
In the Muller-Lyer illusion (above) we tend to
perceive the line on the right as slightly longer than
the one on the left.
The Ponzo Illusion
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Linear perspective
provides context
Side lines seem to
converge
Top line seems farther
away
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But the retinal
images of the red
lines are equal!
Fooling the Eye
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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” in front of face.
Hearing
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What we hear
An ear on the world
Constructing the auditory world
What We Hear
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Loudness
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Pitch
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The dimension of auditory experience related to
the intensity of a pressure wave.
The dimension of auditory experience related to
the frequency of a pressure wave.
Timbre (pronounced “TAM-bur”)
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The distinguishing quality of sound; the
dimension of auditory experience related to the
complexity of the pressure wave.
An Ear on the World
Auditory Localization
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Sounds from different
directions are not identical
as they arrive at left and
right ears
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Loudness
Timing
Phase
The brain calculates a
sound’s location by using
these differences.
Other Senses
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Taste: savoury sensations
Smell: The sense of scents
Senses of the skin
The mystery of pain
The environment within
Taste: Savoury Sensations
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Papillae
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Knoblike elevations on the tongue, containing the
taste buds (Singular: papilla).
Taste buds
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Nests of taste-receptor cells.
Taste Buds
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Photograph of tongue
surface (top),
magnified 75 times.
10,000 taste buds line
the tongue and
mouth.
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Taste receptors are
down inside the
“bud”
Children have more
taste buds than adults.
Four Tastes
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Four basic tastes
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Salty, sour, bitter and sweet.
Different people have different tastes based
on:
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Genetics
Culture
Learning
Food attractiveness
Smell: The Sense of Scents
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Airborne chemical molecules enter the nose and
circulate through the nasal cavity.
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Vapors can also enter through the mouth and pass into
nasal cavity.
Receptors on the roof of the nasal cavity detect these
molecules.
Olfactory System
Sensitivity to Touch
Gate-Control Theory of Pain
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Experience of pain
depends (in part) on
whether the pain
impulse gets past
neurological “gate” in
the spinal cord and
thus reaches the brain.
Neuromatrix Theory of Pain
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Theory that the
matrix of neurons in
the brain is capable of
generating pain (and
other sensations) in
the absence of signals
from sensory nerves.
The Environment Within
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Kinesthesis
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Equilibrium
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The sense of body position and movement of
body parts; also called kinesthesia.
The sense of balance.
Semicircular Canals
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Sense organs in the inner ear, which
contribute to equilibrium by responding to
rotation of the head.
Perceptual Powers: Origins and
Influences
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Inborn abilities
Critical periods
Psychological and cultural Influences on
perception
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Glass surface, with
checkerboard underneath at
different heights
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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 (Gibson &
Walk, 1960)
The Visual
Cliff
The Visual Cliff
Critical Periods
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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 has
hearing may be influenced
similarly.
Psychological and Cultural Influences
on Perception
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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 our previous experiences
influence how we perceive the world.
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Perceptual Set
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A habitual way of perceiving, based on expectations.
All are influenced by our culture.
Perceptual Set
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What you see in the centre figures depends on the
order in which you look at the figures:
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If you scan from the left, see an old woman
If you scan from the right, see a woman’s figure
Context Effects
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The same physical
stimulus can be
interpreted differently
We use other cues in
the situation to
resolve ambiguities
Is this the letter B or
the number 13?
Puzzles of Perception
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Subliminal Perception
Extrasensory Perception: Reality or
Illusion?
Subliminal Perception
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Perceiving without awareness
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visual stimuli can affect your behaviour even
when you are unaware that you saw it
nonconscious processing also occurs in
memory, thinking, and decision making
these effects are often small, however, and
difficult to demonstrate and work best with
simple stimuli
Subliminal Perception
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Perception versus Persuasion
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there is no empirical research to support
popular notions that subliminal persuasion
has any effect on a person’s behaviour
persuasion works best when messages, in the
form of advertising or self-help tapes, are
presented above-threshold, or at a
supraliminal level
Extrasensory Perception
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Extrasensory Perception (ESP):
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The ability to perceive something without
ordinary sensory information
This has not been scientifically demonstrated
Three types of ESP:
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Telepathy – Mind-to-mind communication
Clairvoyance – Perception of remote events
Precognition – Ability to see future events
Parapsychology
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The study of purported psychic phenomena
such as ESP and mental telepathy.
Persinger suggests that psychic phenomena
are related to signs of temporal lobe
epilepsy in otherwise neurologically
normal individuals.
Most ESP studies produce negative
findings and are not easily replicated.
Parapsychology
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J. B. Rhine conducted many experiments on ESP
using stimuli such as these.
Rhine believed that his evidence supported the
existence of ESP, but his findings were flawed.