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Sensation and Perception
©2002 Prentice Hall
Sensation and Perception
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Our Sensational Senses
Vision
Hearing
Other Senses
Perceptual Powers: Origins and Influences
Puzzles of Perception
©2002 Prentice Hall
Sensation and Perception
• Sensation: 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: 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
– Cannot simultaneously
be both
• Brain can interpret the
ambiguous cues two
different ways
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Our Sensational Senses
The Riddle of Separate Sensations
Measuring the Senses
Sensory Adaptations
Sensory Overload
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The Riddle of Separate Sensations
• Sense Receptors: Specialized neurons that
convert physical energy from the environment
or the body into electrical energy that can be
transmitted as nerve impulses to the brain.
• Doctrine of 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.
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Measuring the Senses
• Absolute Threshold
– The smallest quantity of physical energy that
can be reliably detected by an observer
• Difference Threshold
– The smallest difference in stimulation that can
be reliably detected by an observer when two
stimuli are compared; also called Just
Noticeable Difference (JND).
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Absolute Sensory Thresholds
• Vision: A single candle flame from 30 miles on a
dark, clear night
• Hearing: The tick of a watch from 20 feet in total
quiet
• Smell: 1 drop of perfume in a 3-room apartment
• Touch: The wing of a bee on your cheek, dropped
from 1 cm
• Taste: 1 tsp. Sugar in 2 gal. water
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Signal Detection Theory
Stimulus is Present Stimulus is Absent
Response:
“Present”
Hit
Response:
“Absent”
Miss
False
Alarm
Correct
Rejection
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Sensory Adaptations
• Sensory Adaptation: The reduction or
disappearance of sensory responsiveness
that occurs when stimulation is unchanging
or repetitious.
• Sensory Deprivation: The absence of
normal levels of sensory stimulation.
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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: The dimension of visual experience
specified by color names and related to the
wavelength of light.
• Saturation: Vividness or purity of color; the
dimension of visual experience related to the
complexity of light waves.
• Brightness: Lightness and luminance; the
dimension of visual experience related to the
amount of light emitted from or reflected by
an object.
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An Eye on the World
• Retina: Neural tissue lining the back of the
eyeball’s interior, which contains the receptors
for vision.
• Rods: Visual receptors that respond to dim light.
• Cones: Visual receptors involved in color vision.
Most humans have 3 types of cones.
• Dark Adaptation: The process by which visual
receptors become maximally sensitive to light.
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Structures of the Human Eye
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Structures of the Retina
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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 cells in the cortex respond to other shapes
(e.g., bulls-eyes, spirals, faces)
• Feature-detectors: Cells in the visual
cortex that are sensitive to specific features
of the environment.
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How We See Colors
• Trichromatic Theory
• Opponent Process Theory
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Trichromatic Theory
• T. Young (1802) & H.
von Helmholtz (1852)
both proposed that the
eye detects 3 primary
colors
– red, blue, & green
• All other colors can be
derived by combining
these three
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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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VS
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Afterimages
Constructing the Visual World
• Form Perception
• Depth and Distance Perception
• Visual Constancies: When Seeing is
Believing
• Visual Illusions: When Seeing is Misleading
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Gestalt Principles
• Gestalt principles describe the brain’s
organization of sensory building blocks into
meaningful units and patterns.
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Proximity
Closure
Similarity
Continuity
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Depth and Distance Perception
• 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.
• Monocular Cues: Visual cues to depth or
distance that can be used by one eye alone.
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Visual Constancies
• 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
Color constancy
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Visual Illusions
• Illusions are valuable in understanding perception
because they are systematic errors.
– 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.
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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” in front of face.
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Hearing
What We Hear
An Ear on the World
Constructing the Auditory World
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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 (pronounced “TAM-bur”): The
distinguishing quality of sound; the
dimension of auditory experience related to
the complexity of the pressure wave.
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An Ear on the World
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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
• Papillae: Knoblike elevations on the
tongue, containing the taste buds (Singular:
papilla).
• Taste buds: Nests of taste-receptor cells.
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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. ©2002 Prentice Hall
Gate-Control Theory of Pain
• Experience of pain
depends (in part) on
whether the pain
impulse gets past
neurological “gate” in
the spinal cord and thus
reaches the brain.
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Neuromatrix Theory of Pain
• 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.
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The Environment Within
• Kinesthesis: The sense of body position and
movement of body parts; also called
kinesthesia.
• 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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Perceptual Powers: Origins and
Influences
Inborn Abilities and Perceptual Lessons
Psychological and Cultural Influences on
Perception
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The Visual Cliff
• Devised by Eleanor Gibson and
Richard Walk to test depth
perception
• 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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Psychological and Cultural
Influences on Perception
• Needs
• Emotions
• Expectations
– Perceptual Set: A habitual way of perceiving,
based on expectations.
• Beliefs
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Puzzles of Perception
Subliminal Perception
Extrasensory Perception: Reality or Illusion?
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Extrasensory Perception
• Extrasensory Perception (ESP):
– The ability to perceive something without
ordinary sensory information
– This has not been scientifically demonstrated
• Three types of ESP:
– Telepathy – Mind-to-mind communication
– Clairvoyance – Perception of remote events
– Precognition – Ability to see future events
©2002 Prentice Hall