Chapter 4: Sensation and Perception
; Two Sides of the Coin: Sensation and Perception
; Seeing: The Visual System
; Hearing: The Auditory System
; Smell and Taste: The Sensual Sense
; Body Senses
Two Sides of the Coin: Sensation and Perception
Sensation: Our Senses as Detectives
; Transduction: The process of converting an external energy or substance into
electrical activity within neurons (e.g., action potential)
; Sense receptor: Specialized cell responsible for converting external stimuli into
neural activity for a specific sensory system
; Sensory adaptation: (habituation)Activation is greatest when a stimulus is first
Lowest level of a stimulus needed for the nervous system to detect a change 50 percent of the time
Just noticeable difference:
The smallest change in the intensity of a stimulus that we can detect
• Weber’s Law: Stronger the stimulus, the bigger the change needed for a change
in stimulus intensity to be noticeable
Signal Detection Theory
;Theory regarding how stimuli are detected under different conditions ；Signal-to-noise ratio: It becomes harder to detect a signal as background noise increases.
；Response biases: Tendencies to make one type of guess over another when we’re in doubt about whether a weak signal is present or absent under noisy conditions
;Phosphenes: Vivid sensations of light caused by pressure on your eyes ;The rubber hand illusion
;The McGurk effect
; A condition in which people experience cross-modal sensations (e.g., hearing
sounds when see colors)
; Doctrine of specific nerve energies: There are many distinct stimulus energies
(light, sound, touch), but the sensation we experience is determined by the nature
of the sense receptor, not the stimulus.
Perception: When Our Senses Meet Our Brains
A whole is constructed from parts
Processing in which a whole is constructed from parts
The ability to attend to many sense modalities simultaneously
Set formed when expectations influence perceptions; an example of top-down processing Reading the caption “saxophone player” beneath this ambiguous figure tends to produce a different perception than reading the caption “woman.”
Perceive objects as the same size no matter how far away they are from us Shape Constancy
Perceive the shape of a rigid object as constant despite differences in the viewing angle
Perceive color consistently across different levels of lighting
The Role of Attention
Process of selecting one sensory channel and
ignoring or minimizing others
Cocktail party effect •
Failure to detect stimuli that are in plain sight when our attention is focused elsewhere
; Processing of sensory information that occurs below the level of conscious
The Visual System
Light: The Energy of Life
; Hue: Color of light
; Intensity: Brightness
; Additive (mixing light) and subtractive (mixing pigments) color mixing
; The visible spectrum is a subset of the electromagnetic spectrum (ultraviolet -
~400 nanometers to infrared - ~700 nanometers)
The Eye: How We Represent the Visual Realm
; Lens in the eye accommodates to focus on images both near and far by changing
from “fat” to “flat.”
; Lens optimally focuses light on the retina. Retina contains rods and cones filled
; Additional cells in the retina transmit information about light to ganglion cells, and
the axons of these cells combine to form the optic nerve.
; The place where optic nerve connects to the retina is a blind spot, a part of the
visual field that we can’t see.
Nearsighted and Farsighted Eyes
; Results when light is focused
in front of the retina due to cornea being too steep or eyes too long.
; Results when light is focused behind the retina when cornea too flat
or eyes too short.
; Worsens with age.
Rods and Cones
• Allow us to see in color
• Sensitive to detail
• Require more light than rods
• Enable us to see basic shapes and forms
• Allow us to see in low levels of light
Time in dark before rods regain maximum light sensitivity
Visual Perception: Gestalt Principles，Rules governing how we perceive objects as wholes within their overall context
Gestalt Principles: Proximity
Objects physically close to each other tend to be perceived as unified wholes.
Gestalt Principles: Similarity
All things being equal, we see similar objects as comprising a whole, much more so than
Gestalt Principles: Continuity
We still perceive objects as wholes, even if other objects block part of them.
Gestalt Principles: Closure
When partial visual information is present, brains fills in what’s missing.
Gestalt Principles: Symmetry
Perceive objects that are symmetrically arranged as wholes more often than those that
Gestalt Principles: Figure-Ground
Visual Perception: Motion
The brain judges how things in our world are constantly changing by comparing visual
frames, like those in a movie.
Visual Perception: Color
Proposes that we base our color vision on three primary colors—blue, green, and red
; Proposes that we perceive colors in terms of three pairs of opponent colors; either
red or green, blue or yellow, or black or white
Depth perception: Ability to judge distance and three-dimensional relations
; Monocular depth cues:
Stimuli that enable us to judge depth using only one eye
； Relative size
； Texture gradient
； Linear perspective
； Height in plane
； Light and shadow
； Motion parallax
All things being equal, more distant objects look smaller than closer objects. Texture Gradient
The texture of objects becomes less apparent as objects move farther away. Interposition
One object that’s closer blocks our view of an object behind it – infer which one is
We can trace most lines in a scene to a point where they meet—the vanishing point. Lines
in parallel never meet, but they appear to do so at great distances Height in Plane
In a scene, distant objects tend to appear higher, and nearer objects lower Light and Shadow
Objects cast shadows that give us a sense of their three-dimensional form Motion Parallax
Ability to judge the distance of moving objects from their speed
We can also be fooled into seeing motion when it’s not there.
Visual Perception: Depth
; Binocular depth cues:
Stimuli that enable us to judge depth using both eyes
； Binocular disparity: Left and right eyes transmit different information for
near objects but see distant objects similarly.
； Binocular convergence: Look at nearby objects use eye muscles to turn
eyes inward (convergence). Brains aware of how much eyes are
converging - use this information to estimate distance.
Visual Perception: Depth
Depth Perception Appears in Infancy
; We can judge depth as soon as we learn to crawl
； Visual cliff: Infants between 6 and 14 months of age hesitate to crawl
over the glass.
When Perception Deceives Us
When We Can’t See or Perceive Visually
The inability to see; the presence of vision
less than or equal to 20/200. Can result in heightened touch, reorganization of visual cortex
A disorder in which patients can’t seamlessly string still images processed by their brains into the perception of ongoing motion
A deficit in perceiving objects. Results from damage to higher visual cortical areas.
A phenomenon in which blind people still make correct guesses about the visual appearance of things around them. Results from damage to area V1.
Hearing: The Auditory System
Sound: Mechanical Vibration
; Audition (our sense of hearing) is the sense we rely on most after sight
; Sound: vibration traveling through a medium (usually air)
; Pitch corresponds to the frequency of the sound wave.
； High frequency = higher pitch
； Lower frequency = lower pitch
； Measured in hertz (Hz)
Sound: Mechanical Vibration
Amplitude of a sound wave corresponds to loudness.
• Loud noise = increased amplitude
• Measured in decibels (dB)
Sound: Mechanical Vibration
;The outer, middle, and inner ear do different jobs to tranduce sound into neural activity ;The outer ear (pinna and ear canal) tunnels sound waves onto the eardrum, causing the
three small bones in the middle ear to vibrate
;On the other side of the eardrum, the ossicles (hammer, anvil, stirrup) vibrate and
transmit sound to the inner ear
;Process creates pressure in the inner ear, where the cochlea converts vibration into
;Organ of Corti: Tissue containing the hair cells necessary for hearing
;Basilar membrane: Membrane supporting the organ of Corti and hair cells in the cochlea
;Organ or Corti and basilar membrane convert auditory information into action potentials
; Specific place along the basilar membrane hair cells matches a tone with a
; Rate at which neurons fire the action potential reproduces the pitch
; Sets of neurons stagger their responses to follow a pitch. When fire at their
highest rate, slightly out of sync with each other, to reach overall rates up to 5,000
;Different tones excite different areas of the basilar membrane and primary auditory cortex
;High tones—place theory
;Low tones—frequency theory, volley theory
When We Can’t Hear
Smell and Taste: The Sensual Senses
Sense Receptors for Smell
Olfactory receptors in our noses are sensitive to hundreds of different airborne molecules.
Sense Receptors for Taste
; Sense receptors in the tongue that respond to sweet, salty, sour, bitter, umami,
and perhaps fat
; Bumps on the tongue containing numerous taste buds
Five Basic Tastes
Salty, Umami, Sweet, Sour, Bitter
Our Body Senses: Touch, Body Position, and Balance
Three Different Body Senses
Somatosensory system: Responds to light touch, deep pressure, hot and cold temperature, and tissue damage
Proprioception: Muscle position sense: muscles contain sense receptors that detect stretch and others that detect force (helps calculate body location) Vestibular sense: Sense of balance and equilibrium
;Responds to stimuli applied to skin, temperature, and injury
;We sense these with specialized nerve endings in the skin (mechanoreceptors) and free
Skin contains many specialized and free nerve endings that detect mechanical pressure, temperature, and pain.
The Sense of Touch
; Large emotional component to pain not present with touch.
; Pain information activates parts of the limbic system in addition to the
; Pain perception can be reduced by a “stoic” mind-set as well as cultural and
; Idea that pain is blocked or gated from consciousness by neural mechanisms in
; Disorders of pain perception, called pain insensitivities, are associated with an
increased risk of injury.
Body Position and Balance
Ergonomics: Human Engineering
; Many everyday objects aren’t designed optimally to capitalize on humans’
sensory and perceptual capacities.
; The field of human factors optimizes technology to better suit our sensory and