Transcript General Psychology

General Psychology
Chapter 3
Sensation and Perception
Sensation and Perception
 Sensation – process of detecting external
stimuli and changing those stimuli into
nervous system activity
 Perception – cognitive process that
involves the selection, organization, and
interpretation of stimuli
Concepts Related to Sensory
Processes
 Sensory threshold – minimum intensity of
a stimulus that will cause the sense organs
to operate
 Psychophysics – study of relationships
between the physical attributes of stimuli
and psychological experiences they produce
Figure 3.1: Examples of absolute threshold values for the five senses (i.e., these stimuli will
be detected 50 percent of the time).
Concepts Related to Sensory
Processes
 Absolute threshold – physical intensity of
a stimulus that a person reports detecting
50% of the time
 Used to see whether a person’s senses are
operating properly
Concepts Related to Sensory
Processes
• Signal detection theory – states that stimulus
detection is a decision-making process of
determining whether a signal exists against a
background of noise
Thresholds
 Difference threshold – smallest difference
between stimulus attributes that can be
detected
 Just noticeable difference (jnd) – amount
of change in a stimulus that makes it just
noticeably different from what it was
Sensory Adaptation
 Occurs when our sensory experience
decreases with continued exposure to a
stimulus
 Dark adaptation – process in which the visual
receptors become more sensitive to light as we
spend time in the dark
 Light adaptation – process by which our eyes
become more sensitive to dark when we spend
time in the light
Figure 3.8: The dark adaptation curve.
Light:
Stimulus for Vision
 Light – wave of electromagnetic energy
 Wave amplitude – intensity or brightness of light
 Wavelength – distance between any point in a wave
and the corresponding point on next cycle (e.g., peak
to peak), measured in nanometers (nm)
 Determines the color or hue we perceive
 Wave purity – refers to characteristic of saturation
Figure 3.2: Representations of light waves differing in wavelength and wave amplitude.
Figure 3.3: The visible spectrum, in which wavelengths of approximately 380-760
nanometers are visible to the human eye and are perceived as various hues.
Figure 3.4: Relationships between physical characteristics of light and our psychological
experience of that light.
Figure 3.5: The major structures of the human eye.
The Eye:
Receptor for Vision
 Cornea – outer shell of eye
 Protects structures at front of eye
 First point where light rays are bent
 Pupil – opening through which light enters eye
 Iris – colored part of the eye that expands or
contracts, depending on light intensity
 Ciliary muscles – expand or contract to
change shape of the lens to bring image into
focus (accommodation)
Figure 3.6: The major features of the human retina.
The Eye:
Receptor for Vision

The eye is filled with two fluids:
1. Aqueous humor – provides nourishment to
the cornea and other structures at the front of
the eye
2. Vitreous humor – fills the interior of the eye,
behind the lens, where it functions to keep the
eyeball spherical
Vision
 Begins to take place at the retina, where
light energy is transduced to neural energy
Rods
Cones
Photosensitive cells that
are most active in low
levels of illumination
and do not respond
differently to different
wavelengths of light
Photosensitive cells that
operate best at high
levels of illumination
and are responsible for
color vision
The Eye, Con’t.
 Optic Nerve – formed of fibers from
ganglion cells; leaves the eye and starts back
toward other parts of the brain
 Fovea – small area of retina with the best
visual acuity. It is packed with cones cells
(no rods!).
 Blind spot – where nerve impulses from
rods and cones leave the eye
Figure 3.7: This figure provides two ways to locate your blind spot.
Visual Pathway
 Left visual field – everything off to your
left ends up in right occipital lobe
 Right visual field – everything off to your
right ends up in left occipital lobe
 Optic chiasma – sorting of which fibers of
the optic nerve get directed where largely
occurs here
Figure 3.9: Cross Laterality.
Color Vision
 Trichromatic theory – First proposed by
Thomas Young and revised by Herman von
Helmholtz
 The eye contains 3 distinct receptors for color
 Each responds best to one of 3 primary colors of
light: red, blue, and green
 By the careful combination of all 3, all other colors
can be produced
Figure 3.10: The relative sensitivities of three types of cones to lights of differing
wavelengths.
Color Vision
 Opponent-process theory – Ewald Hering
proposed this theory in 1870
 Three pairs of visual mechanisms that respond
to different wavelengths of light
 Blue-yellow processor
 Red-green processor
 Black-white difference/brightness processor
 Each is capable of responding to either of the
two hues that give it its name, but not both
Color Blindness
 In dichromatism, there is a lack of one type
of cone (supporting Young-Helmholtz’s
theory)
 However, color vision defects higher in the
visual pathway support the opponentprocess theory
 Both theories are probably correct, each in
its own way
Gender Differences
in Perception of Color?

Reliable, stable differences in color
preferences:
1. Women prefer “cool colors,” while men
prefer bright, strong colors
2. Women are more likely to have a favorite
color
3. Women can name more colors
4. Color matters more to women.
Sound:
Stimulus for Hearing
 Sound – series of pressures of air (or some
other medium) beating against the ear
 Amplitude – intensity that determines the
psychological experience we call loudness
 Zero point on decibel scale (perceived loudness) is
lowest intensity of sound that can be detected –
absolute threshold
Figure 3.11: Sound waves are manifested as changes in air pressure are produced as the
tines of the tuning fork vibrate back and forth.
Sound, Con’t.
 Frequency – number of waves exerted for
every second of Unit of sound is called
hertz (Hz) {20-20,000 Hz}
 Pitch – how high or low a tone is
(determined by wavelength)
 Purity – timbre is character of sound that
reflects degree of purity
 White noise is a random mixture of sound
frequencies
Figure 3.12: Loudness values in decibel units for various sounds.
Figure 3.13: A summary of the ways in which the physical characteristics of light and sound
waves affect our psychological experiences of vision and hearing.
Ear:
Receptor for Hearing
 Cochlea – major structure of inner ear
 Receptor cells (transducers for hearing) are
here
 When fluid inside cochlea moves, basiliar
membrane is bent up & down, which
stimulates receptors (hair cells)
 Neural impulses travel on auditory nerve
toward temporal lobe
Figure 3.14: The major structures of the human ear.
Chemical Senses
 Taste = gustation
 Four psychological qualities: sweet, salty, sour,
and bitter
 Taste buds – receptor cells for taste on tongue
 We have about 10,000 taste buds
Figure 3.15: Enlarged view of a taste bud, the receptor for gustation.
Chemical Sense, Con’t.
 Smell = Olfaction
 Pheromones – chemicals that many animals
emit that produce distinctive odors that are used
as a method of communication between
organisms
 VNO (vomeronasal organ) – primary organ
used in detection of pheromones. Involved in
mating, territoriality, and aggressiveness in
animals.
Figure 3.16: The olfactory system, showing its proximity to the brain and
transducers for smell — the hair cells.
The Skin-Cutaneous Senses
 A square inch of skin contains nearly 20
million cells
 Some skin receptor cells have free nerve
endings, while others have encapsulated
nerve endings
 Our ability to discriminate among types of
cutaneous sensation is due to a unique
combination of responses the receptor cells
have to various types of stimulation
Figure 3.17: A patch of hairy skin, showing the layers of skin and several nerve cells.
Figure 3.18: A demonstration that our sense of what is hot can be constructed from
sensations of what is warm and cold.
Position Senses
 Vestibular Sense
 Tells us about balance,
where we are in relation to
gravity and about
acceleration or deceleration
 Receptors are located on
either side of the head, near
the inner ear (5 chambers)
 Over-stimulation may result
in motion sickness
 Kinesthetic sense
 Tells us about the position
of various parts of our
bodies and what our
muscles and joints are
doing
 Receptors are located
primarily in our joints, but
some information comes
from muscles and tendons
 Information from these
receptors travels via the
spinal cord
 They provide examples of
reflex reactions
A Special Sense:
Pain
Theories of pain:
1. Gate control mechanism (high in spinal cord)
that opens to let pain messages race to brain or
closes to block messages
2. Cognitive behavioral – pain is influenced by
attitudes, expectations and behaviors
Pain Management
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Drug therapy
Hypnosis & cognitive self-control
Acupuncture
Placebo – a substance a person thinks will
be helpful in treatment
 Counterirritation – stimulating an area of
the body near the location of the pain
Paying Attention:
A Process of Selection
 Salient detail – one that captures our
attention
 Remembered better than peripheral details
(which are part of the perceptual background)
 Stimulus factors make some details more
compelling than others
 Personal factors – characteristics of a
perceiver that influence which stimuli get
attended to
Stimulus Factors
 Contrast – extent to which a stimulus is
physically different from the other stimuli
around it
 Most important factor in perceptual selectivity
 The more intense a stimulus is, the more likely
we are to attend to it
 Motion is another dimension for which contrast
is important
 Repetition can also influence attention
Personal Factors in Processing
 Bottom-Up
Processing
 Attend to a
stimulus,
organize and
identify it, and
then store it in
memory
 Top-Down
Processing
 Motivation,
mental set, and
past experience
influence
perceptual
sensitivity
Figure 3.19: How we perceive the world is determined at least in part by our
mental set, or our expectations about the world.
Gestalt Psychology
 A gestalt forms when one sees the overall
scheme of things: the whole, totality or
configuration.
 Gestalt Psychology – basic principle is
figure-ground relationship
 Of all the stimuli in your environment, those
you attend to and group together are “figures”
 All other stimuli become “ground”
Figure 3.20: (A) A classic reversible figure-ground pattern.
Grouping Stimuli
with Bottom-Up Processing
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Proximity
Similarity
Continuity
Common fate
Closure
Figure 3.21: Four Gestalt psychology examples of grouping.
Figure 3.22: An example of subjective contour.
Grouping Stimuli
with Top-Down Processing
 Perceiving stimuli because we want to,
expect to, or have experienced them
together in the past
 How we ultimately organize our
experiences depends on both types of
processing
Figure 3.23: An example of top-down processing.
Perceiving Depth & Distance
 Ocular cues are built into our visual system
and tell us about depth and distance
 Retinal disparity – each eye gets a
somewhat different view of a 3-dimensional
object
 Convergence – eyes turning in, toward
each other, when something is viewed up
close
Figure 3.24: When looking at a three-dimensional object, such as a pen, the right eye sees a
slightly different image than does the left eye — a phenomenon called retinal disparity.
Monocular Cues
 Physical cues to depth and distance are
those we get from the structure of our
environment
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Linear Perspective
Interposition
Relative Size
Texture gradient
Patterns of Shading
Motion Parallax
Figure 3.25: At the level of the retina, we experience different images; yet we know we are
looking at the same door because of shape constancy.
Constancy of Visual Perception
 Perceptual constancies help us organize
and interpret the stimulus input we get from
our senses. They allow us to see stimuli as
constant, regardless of changing conditions.
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Size constancy
Shape constancy
Brightness constancy
Color constancy
When Constancy Fails…
 Illusions – experiences in which our
perceptions are at odds with what we know
as physical reality
 Illusions remind us that perception is a
higher level process than sensation!
Figure 3.26: A few classic geometrical illusions.
Figure 3.27: Impossible figures — examples of conflicting visual information.
Figure 3.29: Müller-Lyer illusion.
Cultural Bias in Perception?
 Yes! There is a role of culture in the
development of depth perception.
 However, with training, most cultural
differences in the perception of depth
disappear.
Figure 3.28: Which animal — the antelope or the elephant — is the hunter about to spear?