Chapter 3

Chapter 3
Sensation and Perception

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Copyright © 2008 Allyn & Bacon

Chapter 3 Overview
 The process of sensation
 Vision
 Hearing
 Smell and taste
 The skin senses
 Balance and movement
 Influences on perception
 Principles of perception
 Unusual perceptual experiences


The Process of Sensation

 Sensation is the process through
which the senses pick up visual,
auditory, and other sensory stimuli
and transmit them to the brain
 Perception is the process by which
the brain actively organizes and
interprets sensory information


What is the difference between
the absolute threshold and the
difference threshold?
 What is the softest sound you can hear and
the dimmest light you can see?
 How much must the volume be turned up or
down for you to notice a difference in the
loudness of music?
 Researchers in sensory psychology have
performed many experiments to answer
these kinds of questions


Absolute threshold

 The minimum
amount of sensory
stimulation that can
be detected 50% of
the time


Difference threshold

 The smallest increase or decrease in a
physical stimulus required to produce a
difference in sensation that is noticeable
50% of the time
 Just noticeable difference (JND) is the
smallest change in sensation that a person
is able to detect 50% of the time


Weber’s Law

 The JND for all senses depends on a
proportion or percentage of stimulus change
rather than on a fixed amount of change
– A 2% change is needed for a JND in a weight
you are holding
 a 1 lb difference is needed for a JND in a 50 lb weight
 a 2 lb difference is needed for a JND in a 100 lb weight
– Only a 0.33% change is needed for a JND in the
pitch of a sound
– Weber’s law best applies to people with average
sensitivities and to stimuli that are not too
strong or weak

How does transduction enable the
brain to receive sensory
information?
 Sensory receptors are highly specialized cells in
the sense organs that detect and respond to one
type of sensory stimuli and transduce (convert) the
stimuli into neural impulses
 Transduction is the process through which
sensory receptors convert sensory stimulation into
neural impulses
 Sensory adaptation is the process in which
sensory receptors grow accustomed to constant,
unchanging levels of stimuli over time
– e.g., Smokers grow accustomed to smell of cigarettes


Vision
 Our eyes respond to light in
the visible spectrum
– The band of electromagnetic
waves visible to the human
eye
 Electromagnetic waves are
measured in wavelengths
– The distance from the peak of
a light wave to the peak of
the next wave


How does each part of the eye
function in vision?
 Cornea
– Tough, transparent
protective layer that
covers front of eye
– Bends light rays inward
through the pupil
 Lens
– Transparent disk-
shaped structure behind
the iris and pupil
– Changes shape as it
focuses on objects at
varying distances
 This process is called
Accommodation


How does each part of the eye
function in vision?
 Retina
– Contains sensory receptors
for vision
 Rods
– Receptor cells that allow
eye to respond to low
levels of light
 Cones
– Receptor cells that enable
us to see color and fine
detail
 Fovea
– Area at center of retina
that provides the clearest
and sharpest vision
 Blind spot
– Point in each retina where
there are no rods or cones

What path does visual information
take from the retina to the primary
visual cortex?
 Optic nerve
– Caries visual information
from each retina to both
sides of the brain
 Primary visual
cortex
– Part of the brain in
which visual information
is processed
– Feature detectors
respond to specific
visual patterns, such as
lines or angles

How do we detect the difference
between one color and another?

 An apple’s skin looks red
because it absorbs short
wavelengths and reflects
long wavelengths
 Hue
– The specific color perceived
 Saturation
– The purity of a color
 Brightness
– The intensity of the light
energy that is perceived as
a color

What two major theories
attempt to explain color vision?
 Trichromatic Theory
– Three types of cones in the retina each make a
maximal response to one of three colors- blue,
green, or red
 Opponent-Process Theory
– Three kinds of cells respond by increasing or
decreasing their rate of firing when different
colors are present
 Red/green cells
 Yellow/blue cells
 White/black cells

A negative afterimage


Hearing

 Sound requires a medium, such as air
or water, through which to move
 First demonstrated by Robert Boyle in
1660
– Watch in a jar experiment


What determines the pitch and
loudness of sound, and how is each
quality measured?
 Frequency
– The number of cycles completed by a sound wave in one
second
– Determines the pitch of a sound
– Frequency is measured in hertz (Hz)
 Amplitude
– The loudness of sound
– Amplitude is measured in decibels (dB)
 Timbre
– The distinctive quality of a sound that distinguishes it from
other sounds of the same pitch and loudness
– Example: A piano and guitar sound different when playing
the same note

Decibel levels of various sounds
Figure 3.5
The loudness of a sound (its
amplitude) is measured in
decibels. Each increase of 10
decibels makes a sound 10
times louder. A normal
conversation at 3 feet
measures
about 60 decibels, which is
10,000 times louder than a soft
whisper of 20 decibels. Any
exposure to sounds of 130
decibels or higher puts a
person at immediate risk for
hearing damage, but levels as
low as 90 decibels can cause
hearing loss if one is exposed
to them over long periods of
time.

How do the outer ear, middle ear,
and inner ear function in hearing?

 Outer ear
– Visible part of the ear,
consisting of the pinna and
auditory canal
 Middle ear
– Contains the ossicles, which
connect the ear drum to the
oval window and amplify
sound waves
 Inner ear
– Cochlea: Fluid filled chamber
that contains the basilar
membrane and hair cells
– Hair cells: Sensory receptors
for hearing


What two major theories
attempt to explain hearing?
 Place theory
– Each individual pitch is determined by the
particular location along the basilar membrane
of the cochlea that vibrates the most
– Provides a good explanation of how we hear
sounds with frequencies higher than 1000 Hz
 Frequency theory
– Hair cell receptors vibrate the same number of
times per second as the wave sounds that reach
them
– Provides a good explanation of how we hear
low-frequency sounds

Smell and Taste

 Olfaction
– The sense of smell
 Gustation
– The sense of taste


What path does a smell message
take from the nose to the brain?

 Olfactory epithelium
– Two 1-inch square patches
of tissue, one at the top of
each nasal cavity, which
contain olfactory
neurons
 Olfactory bulbs
– Two structures above the
nasal cavity where smell
sensations first register in
the brain
 Orbitofrontal cortex
– Receives messages from
olfactory bulbs via the
thalamus


What are the primary taste
sensations, and how are they
detected?
 Traditionally, four primary taste sensations
have been recognized
– Sweet
– Sour
– Salty
– Bitter
 Recent research suggests that there is a
fifth taste sensation
– Umami
– This sensation is triggered by glutamate


What are the primary taste
sensations, and how are they
detected?

 Taste sensations are detected by receptor cells in the taste buds
 Specialized receptors are activated by each flavor (sweet, sour,
etc.)
– These receptors send separate messages to the brain


The Skin Senses

 Include the senses of touch and pain
 These senses are critical for survival


How does the skin provide
sensory information?
 When an object touches and depresses the
skin it stimulates receptors in the skin
 These receptors send messages through
nerve connections to the spinal cord,
through the brainstem and midbrain, and to
the somatosensory cortex
 Areas on the skin vary in sensitivity to
touch, as measured by the two-point
threshold
– Areas with greater sensitivity are more densely
packed with touch receptors


What is the function of pain, and how is
pain influenced by psychological factors,
culture, and endorphins?
 Pain serves as an early warning system for many
potentially deadly situations
 Pain can be influenced by several psychological
factors
– Focusing attention elsewhere reduces pain
– Placebo effect reduces pain
– Negative thoughts increase pain
– Some cultures encourage individuals to suppress, or
exaggerate, emotional reaction to pain
 Endorphins are the body’s natural painkillers
– They block pain and produce a sense of well-being


Balance and Movement

 The kinesthetic and vestibular
senses provide information about
where the parts of the body are and
where the body is located relative to
the physical environment


What kinds of information do the
kinesthetic and vestibular senses
provide?
 The kinesthetic sense provides
information about the position of body parts
in relation to each other and the movement
of the entire body or its parts
 This information is detected by receptors in
the joints, ligaments, and muscles


What kinds of information do the
kinesthetic and vestibular senses
provide?

 The vestibular sense detects movement and the body’s orientation in space
 The vestibular sense organs are located in the semicircular canals and
vestibular sacs in the inner ear
– These organs sense rotation of the head


Influences on Perception

 Perception is the process through
which the brain assigns meaning to
sensations
 Perception is influenced by a number
of factors, including
– Attention
– Prior knowledge
– Cross-modal perception


What is gained and what is lost
in the process of attention?
 Attention is the process of sorting through
sensations and selecting some of them for further
processing
 When attention is focused on some sensations,
others are missed altogether or misperceived
– Inattentional blindness occurs when attention is
shifted from one object to another and we fail to notice
changes in objects not receiving direct attention
– The cocktail party phenomenon shows that we focus
attention on information that is personally meaningful


How does prior knowledge
influence perception?
 Bottom-up processing
– Information processing in which individual bits of
data are combined until a complete perception is
formed
 Top-down processing
– Information processing in which previous
experience and knowledge are applied to
recognize the whole of a perception
– Perceptual set is an expectation of what will
be perceived that can affect what is perceived


How does information from
multiple sources aid perception?

 Cross modal perception
– The process by which the brain integrates
information from more than one sense
– Cross modal perception is used to process
complex stimuli such as speech


Principles of Perception

 A few principles govern perceptions in
all humans


What are the principles that govern
perceptual organization?

 Gestalt principles of perceptual organization
– Similarity: Objects that have similar characteristics are perceived as a unit
– Proximity: Objects that are close together are perceived as belonging together
– Continuity: Figures or objects are perceived as belonging together if they appear
to form a continuous pattern
– Closure: Figures with gaps in them are perceived as complete
F


What are some of the binocular
and monocular depth cues?
 Depth perception
– The ability to perceive the visual world in three
dimensions and to judge distances accurately
 Binocular depth cues depend on both
eyes working together
– Convergence
– Binocular disparity
 Monocular depth cues can be perceived
by one eye alone


Binocular disparity
 Enables most of us to see 3-D images in stereograms


Monocular depth cues


How does the brain perceive
motion?
 The brain perceives real motion by
comparing the movement of images
across the retina to reference points
that it assumes to be stable
 Autokinetic illusion
– An unmoving light in a dark room appears
to move
 Your eyes are moving, not the light
 In the dark, the brain has no stable reference
point to determine what is moving

What are three types of
puzzling perceptions?

 Ambiguous figures
– The perceptual system tries to resolve the uncertainty by
seeing the figure first one way and then another
 Impossible figures
– May not seem unusual until you examine them closely and
see the impossibility

What are three types of
puzzling perceptions?

 Illusions
– False perceptions or misperceptions of an actual stimulus in the
environment
 Figure c shows the Müller-Lyer illusion

 Figure d shows the Ponzo illusion


Unusual Perceptual
Experiences
 Subliminal perception
– The capacity to perceive and respond to
stimuli that are presented below the
threshold of awareness
 Extrasensory perception (ESP)
– Gaining information about objects,
events, or another person’s thoughts
through means other than known sensory
channels


In what ways does subliminal
perception influence behavior?
 Research suggests that subliminal
information can influence behavior to
some degree
– But it appears to be ineffective at
persuading people to buy products or
vote in certain ways


What have studies of ESP
shown?
 Some studies have suggested that ESP
exists
 But, in almost all cases, attempts to
replicate these studies have failed
– So most psychologists remain skeptical
about existence of ESP


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