By Michael Parker,2014-07-05 09:48
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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



    Absolute threshold:

    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

     Webers 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

Sensory Cross-Modality

    ;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

    Bottom-up processing

    A whole is constructed from parts

Top-down processing

    Processing in which a whole is constructed from parts

Parallel Processing

    The ability to attend to many sense modalities simultaneously

Perceptual set:

    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.”

Perceptual Constancy

    Size Constancy

    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

    Color Constancy

    Perceive color consistently across different levels of lighting

The Role of Attention

    Selective attention:

    Process of selecting one sensory channel and

    ignoring or minimizing others

     Cocktail party effect


Inattentional blindness:

    Failure to detect stimuli that are in plain sight when our attention is focused elsewhere

Subliminal Perception

    ; 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

    with pigments.

    ; 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 cant see.

Nearsighted and Farsighted Eyes

    Nearsightedness (myopia)

    ; Results when light is focused

    in front of the retina due to cornea being too steep or eyes too long.

    Farsightedness (hyperopia)

    ; 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

Dark Adaptation

    Dark adaptation:

    Time in dark before rods regain maximum light sensitivity

Visual Perception

    Visual Perception: Gestalt PrinciplesRules 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

    dissimilar objects.

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 whats 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

    Trichromatic theory:

    Proposes that we base our color vision on three primary colorsblue, green, and red

    Opponent-process theory:

    ; Proposes that we perceive colors in terms of three pairs of opponent colors; either

    red or green, blue or yellow, or black or white

    ; Afterimages

    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

Relative Size

    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 thats closer blocks our view of an object behind it infer which one is


    Linear Perspective

    We can trace most lines in a scene to a point where they meetthe 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 its 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

    Motion blindness:

    A disorder in which patients cant seamlessly string still images processed by their brains into the perception of ongoing motion

    Visual agnosia:

    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)

Common Sounds

    Sound: Mechanical Vibration

    The Ear

    ;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

The Ear

    ;Process creates pressure in the inner ear, where the cochlea converts vibration into

    neural activity

    ;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

Pitch Perception

    ; Specific place along the basilar membrane hair cells matches a tone with a

    specific pitch

    ; 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 tonesplace theory

;Low tonesfrequency 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

    Taste buds:

    ; 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

Somatosensory System

    ;Responds to stimuli applied to skin, temperature, and injury

    ;We sense these with specialized nerve endings in the skin (mechanoreceptors) and free

;nerve endings

    Somatosensory Pathways

    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

    somatosensory cortex.

    ; Pain perception can be reduced by a stoic mind-set as well as cultural and

    genetic factors.

    ; Idea that pain is blocked or gated from consciousness by neural mechanisms in

    spinal cord

    ; 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 arent designed optimally to capitalize on humans

    sensory and perceptual capacities.

    ; The field of human factors optimizes technology to better suit our sensory and

    perceptual capabilities.

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