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Sensation and Perception
Chapter 3
Basic Definitions
 Sensation is the process in which the
sense organ’s receptor cells are
stimulated and relay information to
higher brain centers
 Perception is the process by which an
organism selects and interprets sensory
input so it can acquire meaning
Basic Definitions
 Perceptual systems are sets of
structures, functions and operations by
which people perceive the world
Sensation and Perception
 Modalities
 Dimensions
Example: Vision
Form Color Motion Depth/Space
Psychophysics
 Psychophysics studies the relationship
between physical stimuli and the
conscious experience of them
Psychophysics
 The absolute threshold is the
minimum level of stimulation
necessary to excite a sensory
system
Sensory Thresholds
 The difference threshold is the
amount of change necessary to
report 50% of the time that the
value of a stimulus has changed
Sensory Thresholds
 There are two methods of studying
sensory thresholds
1. Method of limits
2. Method of constant stimuli
Sensory Thresholds
 Signal detection theory holds that an
observer’s perceptions depend on:
 The intensity of a stimulus
 The observer’s motivation, criterion set
by the observer, and background noise
The Visual System
 Humans derive more information
through sight than any other sense
 Light that is visible to the human eye is
a small part of the electromagnetic
spectrum
Figure 3.3 The Electromagnetic Spectrum
Figure 3.4 The Main Structures of the Eye
Structure of the Eye
 The cornea is a small, transparent bulge
covering both the pupil and the iris
 Behind the pupil is the lens
 Together, the cornea, the pupil, the iris,
and the lens focus images onto the
retina
The Retina
 The retina consists of ten layers of cells
including:
 Photoreceptors (light-sensitive cells)
 Bipolar cells
 Ganglion cells
retina
The Retina
 Two types of photoreceptors are rods
and cones
 When photopigments break-down,
electrochemical changes occur in the
photoreceptors
The Retina
 The process by which stimuli are
analyzed and converted into electrical
impulses is called transduction
 In Rods transduction involves the
breakdown of Rhodopsin into
Opsin and Retinol by light hiting
the rod receptor [vitamin A]
The Retina
 Through a process called convergence,
signals from many photoreceptors come
together in a single bipolar cell
The Retina
 From bipolar cells, the energy is
transferred to ganglion cells
 The axons of the ganglion cells make
up the optic nerve which carries
information to the brain
 The first synapse of the ganglion cells
in the brain is in the thalamus’ lateral
geniculate nucleus
The Visual Cortex
 The axons of the ganglion cells make
up the optic nerves which carries
information to the brain
 In the brain, information is processed
by the visual cortex
Duplicity Theory
 Duplicity theory asserts there are two
receptor systems in the retina, the rods
and cones
Rods and Cones
 Cones are used for day vision, colour
vision, and fine discrimination
 Rods are found in the rest of the fovea
and are used primarily for night vision
 Eat your carrots
Rods and Cones
 Dark adaptation is the increase in
sensitivity to light when illumination
decreases
Higher Pathways
 Each eye is connected to both sides
of the brain
 Half an eye’s optic nerve fibres go to
the left side, and half to the right
 The point of the crossover is the
optic chiasm
Figure 3.8 A Visual Image Is Projected to Both
Hemispheres of the Brain
Electrochemical Basis of
Perception
 Receptive fields are areas of the retina
that, when stimulated, produce a
change in the firing of cells in the visual
system
Electrochemical Basis of
Perception
 Hubel and Wiesel describe three types
of feature detectors
 The first type is simple cells
 The second type is complex cells
 The third type is hypercomplex cells
Eye Movements
 Saccades are rapid, voluntary eye
movements and the most common
type of eye movements
 The delay of 200 to 250 msecs
between saccades is a fixation
Colour Vision
 When people speak of the color of an
object, they are referring to hue
 Hue is a psychological term, because
objects themselves do not possess
colour
 Colour is determined by how the eyes
and brain interpret reflected
wavelengths of light
Colour Vision
 One psychological dimension of
colour is hue
 A different hue is associated with
each wavelength
Colour Vision
 A second psychological dimension is
brightness or how light or dark the hue
of an object appears
 The third psychological dimension of
colour is saturation or purity
Theories of Colour Perception
 The trichromatic theory developed by
Young and Helmholtz
 The opponent process theory
developed by Herring
Trichromatic Theory
 Trichromatic theory says mixing
three basic colours can make all
colours
 Three types of cones are especially
sensitive to red, green, and blue
 If the neural output from one type of
cone is greater than the others, that
receptor has a stronger influence on
the colour perceived
Opponent Process Theory
 Opponent process theory assumes
there are six colours and three types of
receptors: red-green, blue-yellow, blackwhite
 Each receptor fires in response to all
wavelengths
 In each pair, one receptor fires more
strongly than the other
Colour Blindness
 Trichromats are people who can
perceive all three primary colours and
can see any hue
 Monochromats are totally colour blind
(less than 1% of the population)
 Dichromats have difficulty distinguishing
either red and green or blue and yellow
Visual Perception
 Size constancy is the ability of the visual
perceptual system to recognize an
object remains constant in size
determined by:
 Previous experience with the true size of
the object
 Distance between the object and the
person
 The presence of surrounding objects
Visual Perception
Shape constancy is the ability of the
visual system to recognize a shape
despite changes in its orientation or
the angle from which it is viewed
Depth Perception
 Depth perception allows a person to
estimate distance from an object, and
the distance between objects
Depth Perception
 Monocular cues do not depend on the
use of both eyes
 Motion parallax occurs when a
moving observer stares at a fixed
point
 Objects behind the point appear to
move in the same direction as the
observer
Depth Perception
 A second monocular depth cue is the
kinetic depth effect
 In the kinetic depth effect, objects which
look flat when stationary appear to be
three dimensional when set in motion
Depth Perception
 Other monocular cues arise from the
stimulus itself
 In linear perspective, larger or taller
objects are perceived as closer
 Linear perspective makes distant
objects appear closer together
Depth Perception
 Interposition is when one object
blocks out another, it seems closer
 Texture is surfaces that have little
texture or detail seem more distant
Depth Perception
 In highlighting and shadowing, light
objects appear near, dark objects
seem distant
 Atmospheric perspective relates to
wavelengths of light, with distant
objects appearing more “blue”
Depth Perception
 Accommodation is changes in the
shape of the lens of the eye as distance
to an object changes
Depth Perception
 Binocular depth cues require the use of
both eyes
 Retinal disparity is a slight difference in
the visual images on the retinas
 Convergence is movement of the eyes
toward each other to keep visual
stimulation at corresponding points on
the retinas as an object moves closer
Sound
 Sound is the psychological experience
that occurs when changes in air
pressure affect the receptive organ for
hearing
 Frequency is the number of complete
changes in air pressure that occurs
during a given unit of time
Sound
 Pitch is the psychological
experience that corresponds with
the frequency of an auditory
stimulus
Sound
 Amplitude (intensity) is the total energy
of a sound wave
 Amplitude determines the loudness of
sound
Sound
 Timbre is the quality of a sound (the
specific mixture of amplitudes and
frequencies that make-up a sound)
Structure of the Ear
 The receptive organ for audition is
the ear
 The ear translates physical stimuli
(sound waves) into electrical
impulses the brain can interpret
 The ear has three major parts: the
outer ear, middle ear, and inner ear
Figure 3.24 The Major Structures of the Ear
Structure of the Ear
 The eardrum (tympanic membrane)
is the boundary between the outer
and middle ear
 The eardrum responds to sound
waves by vibrating
 Large forces striking the eardrum
are converted to smaller forces by
the bones (ossicles) of the middle
ear
Structure of the Ear
 The three bones of the middle ear
stimulate the basilar membrane, which
runs down the middle of the cochlea
 Sound waves of different frequencies
stimulate different areas of the basilar
membrane
Structure of the Ear
 The cells are responsible for the
transduction of mechanical energy into
neural impulses
 Neural impulses travel via the auditory
nerve to the midbrain, then to the
auditory cortex
Theories of Hearing
 Place theories claim the analysis of
sound occurs in the basilar membrane
 Different frequencies and intensities
effect different parts (places) of the
membrane
Theories of Hearing
 Frequency theories say the analysis of
pitch and intensity occur at higher
centers of processing
 Frequency theories say the basilar
membrane merely transfers information
Sound Localization
 Sound localization involves detecting
where a sound comes from
 Sounds produced to the left of the
head arrive at the left ear before the
right side
Hearing Impairments
 Conduction deafness results from
interference with the transmission of
sound to the neural mechanism of the
inner ear
 Sensorineural deafness results from
damage to the cochlea, the auditory
nerve, or higher auditory processing
centres
Taste
 Taste is a “chemical” sense in which
food partially dissolved in saliva
stimulates taste buds
 All taste cells are sensitive to all taste
stimuli, but some are more sensitive to
specific taste stimuli
 There are four basic taste stimuli:
sweet, sour, salty, bitter
Taste
 Taste sensitivity seems to be genetically
determined
 Taste also depends on the number of
taste buds a person has
 Past experience is also important in the
taste of foods
Smell
 Like taste, olfaction (the sense of smell)
is a chemical sense
 The receptors for smell are the olfactory
receptor cells contained in the olfactory
epithelium
Smell
 The olfactory bulbs are enlargements
of the olfactory nerve
 The olfactory nerve transmits
information to the brain
Smell and Communication
 Pheromones may influence the
physiology of another animal
 They are widely recognized as
initiators of sexual activity among
animals
Touch
 The skins consists of three layers:
 The epidermis, the top layer,
consists primarily of dead cells
 The second layer, the dermis,
contains living cells
 The inner layer, the hypodermis, is a
thick, insulating cushion
Pain
 Pain is due to the operation of free
nerve endings, microscopic ends of
afferent neurons not connected to any
specific organ
 The perception of pain is both physical
and psychological
Pain
 Neuromatrix theory contends the brain
possesses a neural network, the
body-self neuromatrix (BSN)
 The BSN integrates inputs to produce
an output pattern we experience as
pain
Pain
 A second influence is visual and
other sensory inputs that influence
the interpretation of the situation
 A third influence is activity of the
body’s stress regulation system
Endorphins
 Endorphins are painkillers that are
produced naturally in the brain and
pituitary gland
 Endorphins bind themselves to receptor
sites in the brain and spinal cord
 Endorphins prevent pain signals from
passing to higher levels of the nervous
system
Acupuncture
 In acupuncture, long, slender needles
are inserted into the body at specific
locations
 Acupuncture may stimulate a release
of endorphins
 It may be effective with migraines,
arthritis, and postoperative pain from
dental surgery
Pain Management
 For people with chronic pain, drug
treatment may be ineffective or even
dangerous because high doses may be
needed
Kinesthesis
 Kinesthesis is the awareness of
movements of the muscles, tendons,
and joints
 Kinesthesis is based on proprioceptive
cues or sensory cues that come from
within the body
The Vestibular Sense
 The vestibular sense is the sense of
bodily orientation and postural
adjustment
 It helps maintain balance and sense
of equilibrium, and provides
information about orientations of head
and body
 Essential structures are in the ear
Extrasensory Perception
 ESP includes four phenomenon:
 Telepathy (transfer of thoughts from
one person to another)
 Clairvoyance (recognizing objects or
events not discernable by normal
sensory receptors)
Extrasensory Perception
 Precognition (inexplicable knowledge
of future events)
 Psychokinesis (ability to move objects
with mental powers