Sensation and Perception
Chapter 3
Part I
William G. Huitt
Last revised: May 2005
Sensation and Perception
• Sensation
– The process through which the senses pick up
visual, auditory, and other sensory stimuli and
transmit them to the brain; sensory information that
has registered in the brain but has not been
interpreted
• Perception
– The process by which sensory information is
actively organized and interpreted by the brain
Process of Sensation
• 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)
– The smallest change in sensation that a person is
able to detect 50% of the time
Process of Sensation
• Ernst Weber
– Observed that the JND for all the senses
depends on a proportion or percentage of
change rather than a fixed amount of
change
– Observation known as Weber’s law
Process of Sensation
• Sensory receptors
– Specialized cells in the sense organs that detect
and respond to sensory stimuli—light, sound,
odors—and transduce (convert) the stimuli into
neural impulses
– Provide the essential link between the physical
sensory world and the brain
• Transduction
– Process where the receptors change or convert the
sensory stimulation into neural impulses
Process of Sensation
• Sensory adaptation
– The process of becoming less sensitive to an
unchanging sensory stimulus over time
– Allows you to shift your attention to what is most
important at any given moment
Vision
Vision
Vision
Vision
• Rods
– Allow humans to see in black, white, and shades of
gray in dim light
– Mostly in the periphery
– Take 20 – 30 minutes to fully adapt to darkness
• Cones
– Enable humans to see color and fine detail in
adequate light, but that do not function in dim light
– Mostly in the fovea
– Adapt fully to darkness in 2 – 3 minutes
Vision
• Trichromatic theory
– First proposed by Thomas Young in 1802 and
modified by Hermann von Helmholtz about 50 years
later
– The theory of color vision suggesting that there are
three types of cones, which are maximally sensitive
to red, green, or blue, and that varying levels of
activity in these receptors can produce all of the
colors
Vision
Three Types of Cones
S-Cones
(Sensitive to blue)
M-Cones
(Sensitive to Green)
L-Cones
(Sensitive to Red)
Vision
• Hue
– The property of light commonly referred to as color,
determined primarily by the wavelength of light
reflected from a surface
• Saturation
– The degree to which light waves producing a color
are of the same wavelength; the purity of a color
• Brightness
– The dimension of visual sensation that is dependent
on the intensity of light reflected from a surface and
that corresponds to the amplitude of the light wave
Vision
• Opponent-process theory
– The theory that three classes of cells increase their
firing rate to signal one color and decrease their
firing rate to signal the opposing color (red/green,
yellow/blue, white/black)
• Afterimage
– After you have stared at one color in an opponentprocess pair (red/green, yellow/blue, black/white),
the cell responding to that color tires and the
opponent cell begins to fire, producing the
afterimage
Vision
Hearing
Hearing
• Audition
– The sensation of hearing; the process of hearing
• Robert Boyle
– Demonstrated that sound requires a medium through
which to move, such as air, water, or a solid object
• Frequency
– Measured in the unit called the hertz, the number of
sound waves or cycles per second, determining the
pitch of the sound
– The human ear can hear sound frequencies from low
bass tones of around 20 Hz to high-pitched sounds of
about 20,000 Hz
Hearing
• Amplitude
– Measured in decibels, the magnitude or intensity of
a sound wave, determining the loudness of the
sound; the amplitude of a light wave affects the
brightness of a visual stimulus
– The measuring unit used, bel, is named after
Alexander Graham Bell
• Decibel
– A unit of measurement of the intensity or loudness
of sound based on the amplitude of the sound wave
Hearing
Hearing
• Timbre
– The distinctive quality of a sound that distinguishes
it from other sounds of the same pitch and loudness
– Human voices vary in timbre, providing us with a
way of recognizing individuals when we can’t see
their faces
– Timbres also vary from one instrument to another
Hearing
• Inner ear
– The innermost portion of the ear, containing the
cochlea, the vestibular sacs, and the semicircular
canals
– Cochlea
• The snail-shaped, fluid-filled chamber in the inner ear that
contains the hair cells (the sound receptors)
– Hair cells
• Sensory receptors for hearing, found in the cochlea
Smell and Taste
• Olfaction
– The sensation of smell; the process of smelling
– You cannot smell a substance unless some of its
molecules vaporize
• Olfactory epithelium
– Two 1-square-inch patches of tissue, one at the top
of each nasal cavity, which together contain about
10 million olfactory neurons, the receptors for smell
• Olfactory bulbs
– Two matchstick-sized structures above the nasal
cavities, where smell sensations first register in the
brain
Smell and Taste
Smell and Taste
• Pheromones
– Chemicals excreted by humans and other animals
that act as signals to, and elicit certain patterns of,
behavior from members of the same species
– Used by animals to mark off territories and to signal
sexual receptivity
• Karl Grammer
– Suggested that humans, although not consciously
aware of it, respond to pheromones when it comes
to mating
Smell and Taste
• Gustation
– The sensation of taste
• Five basic tastes
–
–
–
–
–
Sweet
Sour
Salty
Bitter
Umami
• Triggered by the substance glutamate (monosodium
glutamate is commercial product)
Smell and Taste
Skin Senses
• Skin
– The largest organ of your body
– Performs many important biological functions while
also providing much of what is known as sensual
pleasure
• Tactile
– Pertaining to the sense of touch
– Information that is conveyed to the brain when an
object touches and depresses the skin, stimulating
one or more of the several distinct types of
receptors found in the nerve endings
Skin Senses
Skin Senses
• Pain
– Motivates us to tend to injuries, to restrict activity,
and to seek medical help
– Teaches us to avoid pain-producing circumstances
in the future
• Chronic pain
– Pain that persists for three months or more
– Three common types
• Low-back
• Headache
• Arthritis
Skin Senses
• Melzack and Wall
– Gate-control theory
• Contend that there is an area in the spinal cord that can act
like a “gate” and either inhibit pain messages or transmit
them to the brain
• You feel pain when pain messages carried by the small,
slow-conducting nerve fibers reach the gate and cause it to
open
• Contend that messages from the brain to the spinal cord can
inhibit the transmission of pain messages at the spinal gate
and thereby affect the perception of pain
Skin Senses
• Endorphins
– Chemicals, produced naturally by the pituitary
gland, that reduce pain and positively affect mood
– Some people release endorphins even when they
only think they are receiving pain medication but are
given, instead, a placebo in the form of a sugar pill
or an injection of saline solution
Spatial Orientation Senses
• Kinesthetic sense
– The sense providing information about relative
position and movement of body parts
– Gives the position of body parts in relation to each
other and the movement of the entire body and/or
its parts
• Vestibular sense
– The sense that provides information about the
body’s movement and orientation in space through
sensory receptors in the semicircular canals and the
vestibular sacs, which detect changes in the
movement and orientation of the head