Download Introducing Psychology

Sensation and Perception
Chapter 6
Copyright © 2010 Pearson Education Canada
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Chapter Outline
• Our Sensational Senses
• Vision
• Hearing
• Other Senses
• Perceptual Powers: Origins and Influences
• Puzzles of Perception
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Sensation & Perception
• 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
– Process by which the brain organizes and interprets
sensory information
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Separate Sensations?
• Sense receptors
– 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
• Dendrites of sensory
neurons responsible for
smell, pressure, pain, &
temperature
• Specialized cells for vision,
hearing, taste
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Separate Sensations?
• Doctrine of specific nerve energies
– Principle that different sensory modalities exist because
signals received by the sense organs stimulate different
nerve pathways leading to different areas of the brain
– If possible, allows for sensory substitution
– Sensory crossover also occurs in synesthesia where
stimulation of one sense consistently evokes a sensation
in another
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Measuring the Senses
• Psychophysics
– Field concerned with how the physical
properties of stimuli are related to our
psychological experience of them
– Commonly relies on measuring absolute
threshold, difference threshold, and applying
signal-detection theory
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Measuring the Senses
• Absolute threshold
– The smallest quantity of physical energy that can be
reliably detected by an observer (50% of the time)
– Senses are sharp, but only tuned into narrow band of
physical energies
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Measuring the Senses
• Difference threshold
– The smallest difference in stimulation that can reliably be
detected by an observer when two stimuli are compared
– Also called just noticeable difference (JND)
• Signal detection theory
– Divides the detection of
sensory signals into a
sensory process and a
decision process
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Sensory Adaptation & Deprivation
• Sensory adaptation
– Reduction or disappearance of sensory responsiveness
when stimulation is unchanging or repetitious
– Useful as spares us from responding to unimportant
information
• Sensory deprivation
– The absence of normal levels of sensory stimulation
– Varied responses somewhat dependant on expectations
& interpretations (e.g., hallucinations)
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Sensing Without Perceiving
• Selective attention
– Focusing of attention on selected aspects of the
environment and blocking out the others
• Inattentional blindness
– Failure to consciously perceive something
you are looking at because you are not
attending to it
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Vision
• Light stimuli (waves) have physical characteristics
that affect three psychological dimensions of our
visual world:
1. Hue
– Dimension of visual
experience
specified by colour
names
– Related to the
wavelength of light
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Vision
2. Brightness
– Dimension of visual experience related to the amount
of light emitted from or reflected by an object
– Related to amplitude of wavelength
3. Saturation
– Dimension of visual experience related to the
complexity of light waves
– Vividness or purity of colour
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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: Widens or dilates
to let in more light
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Visual Receptors
• 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
colour vision
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The Retina
• We experience chemical changes in rods & cones
when our eyes adjust fully to dim illumination
(called dark adaptation)
• Retinal processing also involves ganglion cells
– Neurons in the retina that gather information from
receptor cells (by way of intermediary bipolar cells)
– Axons form the optic nerve which leaves the eye at the
optic disk (location of blind spot)
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Structures of the Retina
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Vision is Not Like a Camera
• Visual processing is an active process & involves
many types of cells in different brain regions
– Cortical cells respond to lines of specific orientations,
others respond to properties of shapes & arrangements
(e.g., spirals, faces)
• Feature detector cells
– Cells in the visual cortex that are sensitive to specific
features of the environment
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How We See Colour
• Trichromatic theory
– Proposes three basic types of cones, each sensitive to a
certain range of wavelengths (red, blue, green)
– Interaction assumed to produce all the different
experiences of hue
• Opponent-process theory
– Assumes that the visual system treats pairs of colours as
opposing or antagonistic
– Occurs in the ganglion cells, and neurons in thalamus &
visual cortex
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Negative Afterimages
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Constructing the Visual World
• We rely on various Gestalt principles to organize
visual input
• Figure: item of interest
that stands out from
the rest of the
environment
• Ground: environment
or background
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Gestalt Principles
1. Proximity: things near each other tend to be grouped
together
2. Closure: the brain fills in gaps to perceive complete forms
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Gestalt Principles
3. Similarity: things that
are alike are perceived
together
4. Continuity: lines & patterns tend to be perceived as
continuing in time or space
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Binocular Cues
• Binocular cues provide visual cues to depth
or distance requiring two eyes
– Convergence: the 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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Monocular Cues
• Monocular cues are visual cues to depth or
distance that can be used by one eye alone
– Light and shadow, interposition, motion
parallax, relative size, relative clarity, texture
gradients, linear perspective
• See Pages 210-211 in your text for descriptions
and images
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Visual Constancies
• Another important perceptual skill is
perceptual constancy
– The accurate perception of objects as stable or
unchanged despite changes in the sensory
patterns they produce
– Best-studied are shape, location, size,
brightness, and colour constancies
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Visual Illusions
• Our systems are sometimes
fooled when making sense
of the world
• Perceptual illusions give us
information about perceptual
strategies used by brain,
and how misleading
messages are interpreted
• Many classic visual illusions
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Visual Illusions
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Visual Illusions
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Hearing
• Audition refers to our sense of hearing
• Three physical characteristics of sound waves that
alter psychological experience of sound:
a) Loudness: intensity/amplitude of pressure wave (dB)
b) Pitch: frequency of pressure waves (Hz); height or
depth of tone
c) Timbre: complexity of the pressure wave;
distinguishing quality of sound
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An Ear on the World
• Cochlea
– Snail-shaped, fluid-filled organ in the inner ear,
containing the structure where the receptors for hearing
are located
• Organ of Corti
– Structure in the cochlea containing the hair cells that are
the auditory receptors
• Basilar membrane
– Rubbery membrane that stretches across the interior of
the cochlea in which the hair cells are embedded
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Structures of the Ear
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Constructing the Auditory World
• Patterns of sound also organized to construct
meaningful patterns
• Gestalt principles can also relate to sound
perception
– e.g., Cdn researcher Bregman & “auditory scenes”
• Sound localization – relies on loudness and
intensity of stimuli to tell us where a sound is
coming from
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Taste (Gustation)
• Papillae
– Knoblike elevations on the tongue
– Contains the taste buds (taste receptor cells)
– 5 main tastes: salty, sour, bitter, sweet, umami
• Genetic differences
in amount and
sensitivity of taste
buds
• Culture, learning, & food attractiveness influence preferences
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Smell (Olfaction)
• Receptors in
each nasal
cavity respond
to chemical
molecules in air
– Trigger
reactions in
olfactory bulb &
higher brain
regions
– Detect around
10,000 smells
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Skin Sensations
• Basic skin senses:
– Touch (pressure), warmth, cold, pain
– Certain spots on skin especially sensitive to 4
basic sensations
• Pain differs from other skin senses
– When stimulus producing pain is removed, the
sensation may continue (e.g., chronic pain)
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Theories of Pain
• Gate-control theory
of pain
– The experience of
pain depends in part
on whether pain
impulses get past a
neurological “gate”
in the spinal cord
and reach the brain
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Theories of Pain
• Neuromatrix theory
of pain
– Matrix of neurons in
the brain is capable
of generating pain
(& other sensations)
in the absence of
signals from sensory
nerves
– Accounts for
phantom pain
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The Environment Within
• Kinesthesis
– Sense of body position and movement of body
parts (also called kinesthesia)
• Equilibrium
– Sense of balance
– Influenced by semicircular canals: sense organs
in the inner ear the contribute to equilibrium by
responding to rotation of the head
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Perceptual Powers
• Is perception hard-wired or influenced by learning?
• Inborn abilities:
– Infants born with
basic sensory
abilities which
rapidly develop
– Depth perception
& visual cliff
experiments
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Perceptual Powers
• Critical periods:
– Crucial windows of time
during which a person
must have certain
experiences or perception
will be impaired
– Classic studies with kittens
in controlled environments
(visual perception)
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Psychological & Cultural Influences
• Perception is also influenced by:
1. Needs: more likely to perceive something when we
need or have an interest in it
2. Beliefs: what we believe can affect what we perceive
3. Emotions: can influence interpretations of sensory
information (especially pain & fear)
4. Expectations: previous experiences influence what we
perceive (e.g., perceptual set)
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Puzzles of Perception
• Perceiving without awareness (subliminal
perception)
– Visual stimuli can affect behaviour even when you are
unaware that you saw it (priming)
– Nonconscious processes influence perception, memory,
thinking, decision-making
– Subliminal persuasion attempts (e.g., theatre study)
often don’t consider person’s motivation (placebo
effects)
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Puzzles of Perception
• Extrasensory perception (ESP)
– Claims that some can send & receive messages
about the world without relying on the usual
sensory channels (limited empirical support)
• Parapsychology
– Study of purported psychic phenomena such as
ESP & mental telepathy
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End of Chapter 6
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