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Sensation & Perception
The Major Senses
There are 6 major senses
hearing
taste
Vision
smell
pain
balance, joint senses, and others
Principles of Sensation
 Transduction—physical
energy to
neural signal
 Absolute threshold—smallest
strength of a stimulus that can be
detected
 Difference threshold—(jnd) smallest
difference that can be detected
 Sensory adaptation
Vision
Purpose of the visual system
–transform light energy into an
electro-chemical neural response
–represent characteristics of objects
in our environment such as size,
color, shape, and location
Distribution of Rods and Cones
 Cones
—concentrated in center
of eye (fovea)
–approx. 6 million
 Rods—
concentrated in periphery
–approx. 120 million
 Blind spot— region with no rods
or cones
Differences Between
Rods and Cones
 Cones
– allow us to see in bright light
– allow us to see fine spatial detail
– allow us to see different colors
 Rods
– allow us to see in dim light
– can not see fine spatial detail
– can not see different colors
Rods
Cones
Processing Visual Information
 Bipolar
cells—neurons that connect
rods and cones to the ganglion cells
 Ganglion cells—neurons that connect
to the bipolar cells; their axons form
the optic nerve
 Optic chiasm—point in the brain
where the optic nerves from each
eye meet and partly crossover to
opposite sides of the brain
Color Vision
 Our
visual system interprets
differences in the wavelength of
light as color
 Rods are color blind, but with
the cones we can see different
colors
 This difference occurs because
we have only one type of rod but
three types of cones
Trichromatic Theory
of Color Vision


Researchers found that by mixing only three
primary lights (usually red, green and blue), they
could create the perceptual experience of all
possible colors
This lead Young and Helmholtz to propose that we
have three different types of photoreceptors, each
most sensitive to a different range of wavelengths
Complementary
Afterimages
Opponent-Process Theory

To account for phenomena like
complementary afterimages, Herring
proposed that we have two types of
color opponent cells
– red-green opponent cells
– blue-yellow opponent cells

Our current view of color vision is that
it is based on both the trichromatic and
opponent process theory
Hearing
Hearing: Sound Waves
 Auditory
perception occurs when
sound waves interact with the
structures of the ear
 Sound Wave—changes over time in
the pressure of an elastic medium
(for example, air or water)
 Without air (or another elastic
medium) there can be no sound
waves, and thus no sound
Intensity of Various Sounds
Example
Softest detectable sound
P (in soundpressure units) Log P Decibels
1
0
0
10
1
20
100
2
40
1000
3
60
Loud music from a radio
10,000
4
80
Heavy automobile traffic
100,000
5
100
1,000,000
6
120
10,000,000
7
140
100,000,000
8
160
1,000,000,000
9
180
Soft whisper
Quiet neighborhood
Average conversation
Very loud thunder
Jet airplane taking off
Loudest rock band on record
Spacecraft launch 9 from 150 ft.
Anatomy of Ear
Purpose of the structures in
the ear:
–Measure the frequency (pitch)
of sound waves
–Measure the amplitude
(loudness) of sound waves
Anatomy of the Ear
Transduction of Sounds
 The
structures of the ear transform
changes in air pressure (sound waves)
into vibrations of the Basilar Membrane
 As the Basilar Membrane vibrates it
causes the hairs in the Hair Cells to
bend
 The bending of the hairs leads to a
change in the electrical potential within
the cell
Chemical and Body Senses
 Olfaction
(smell)
 Gustation (taste)
 Touch and temperature
 Pain
 Kinesthetic (location of body)
 Vestibular (balance)
Taste
• Sweet
• Sour
• Salty
• Bitter
• Umami ("meaty",
"savory" or "broth-like")
Skin and Body Senses




Pressure—Pacinian corpuscles
Temperature—receptors reactive to cold or
warm, simultaneous stimulation produces
sensation of hot
Pain—free nerve endings are receptors that
send message to the spinal cord releasing
substance P
Gate control theory of pain is most influential
Pain Gate
Movement, Position, and
Balance
 Kinesthetic—sense
of location of
body parts in relation to each
other
 Vestibular—sense of balance,
receptors located in the inner ear
 Proprioceptors—receptors in
muscles and joints that provide
information about body position
and movement
 Perception2.ppt