Download General Psychology: Sensation

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
• 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
• 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
Hearing
• Middle Ear
– Contains the ear drum. When sound hits the
drum it vibrates to cause small bones to
vibrate which activates the inner ear
receptors.
• External Ear
– The cupped shape of the ear catches sound
waves and channels them to the eardrum.
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)
Taste
• Taste receptors
– Occur in taste buds
• Most are found on the surface of the tongue
• Homeostasis- taste is what keeps are
body protected from what is going into are
bodies.
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 is responsible for
•
•
•
•
•
Regulating body temperature.
Storing water and fat.
Is a sensory organ.
Preventing water loss.
Preventing entry of bacteria.
Parts of Skin
• The skin is made up of the following
layers, with each layer performing specific
functions:
– Epidermis: The epidermis is the thin outer layer of the
skin containing hair follicles. This layer of the skin
contains touch receptors.
– Dermis
– Subcutaneous fat layer (subcutis)
Dermis
• Touch sensation originates in the bottom layer of
your skin called the dermis.
• The dermis is filled with many tiny nerve endings
which give you information about the things with
which your body comes in contact. They do this
by carrying the information to the spinal cord,
which sends messages to the brain where the
feeling is registered.
Receptors
• The nerve endings in your skin can tell you if something
is hot or cold. They can also feel if something is hurting
you.
• Your body has about twenty differnt types of nerve
endings that all send messages to your brain. However,
the most common receptors are heat, cold, pain, and
pressure or touch receptors. Pain receptors are probably
the most important for your safety because they can
protect you by warning your brain that your body is hurt!
Skin Facts
• You have more pain nerve endings than any other type.
• The least sensitive part of your body is the middle of
your back.
• The most sensitive areas of your body are your hands,
lips, face, neck, tongue, fingertips and feet.
• Shivering is a way your body has of trying to get warmer.
• There are about 100 touch receptors in each of your
fingertips.
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
• 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