Color

Chapter 7
Nature of Color
Color Mixing
Anatomy and Physiology of Color Vision
Individual Differences in Color Vision
Color Phenomena
Nature of Color
 Nature of Color

What is the evolutionary significance of

color vision?
Nature of Color
 Nature of Color
Light is the portion of the electromagnetic
radiation spectrum made up of waves that range
from about 400nm (violet) to 700 nm (red)
Nature of Color
 Nature of Color
• The light that reaches our eyes indirectly, after
it is reflected off a surface, tend to reflect
selected portions of the spectrum while
absorbing others.
 Nature of Color
• An object’s color has several components:
– Hue: related to wavelength
– Saturation: related to purity
– Lightness: related to reflectance (albedo)
– Brightness: related to intensity
• Hue, saturation, lightness, and brightness are
perceptual terms, wavelength, purity,
reflectance, and intensity are physical terms.
 Nature of Color
• Wavelength is the distance light travels during
one cycle (crest to crest) typically measure in
nanometers (one billionth of a meter)
• Amplitude is the height of the light wave
 Nature of Color
• So the colors we perceive are partially
determined by the nature of the light falling
on the surface (illumination) and the nature of
the absorption and reflectance of the surface.
 Nature of Color
• Color wheel is a way
to organize colors
– Circle with all the
different
wavelengths
arranged around the
edge
• Nonspectral hues:
cannot be described
in terms of a single
wavelength
 Nature of Color
• Color solid or color
spindle represents hue,
lightness, and saturation
– Achromatic color (white,
grays, black) along center
axis
– Horizontal section at any
point produces color wheel
associated with that
lightness
– Newton’s color wheel is
along the horizontal center
 Nature of Color
• The center of Newton’s
color wheel would be a
medium gray.
• All colors within a cross
section are of equal
lightness
• Physical purity is the
amount of achromatic light
added to monochromatic
light
Color Mixing
 Color Mixing
• Subtractive mixture: dyes and pigments
(paint) involving only a single light source
• Additive mixture: beams of light from separate
light sources
 Subtractive Mixtures
• Subtractive because
when light falls on a
pigment (or passes
through a colored
filter) parts of the
spectrum are
absorbed or
subtracted.
 Subtractive Mixtures
• The result of a mixture depends on what
wavelengths don’t get absorbed by the two
pigments
Amount of reflection

blue green yellow red

wavelength
 Subtractive Mixtures
• Both yellow and blue pigments reflect a bit of
green
Amount of reflection

blue green yellow red

wavelength
Subtractive Mixtures

ch 9 19
 Subtractive Mixtures
• Subtractive mixing is commonly used in color
printers and picking paint at Home Depot
 Additive Mixtures
• Combining lights not
pigments.
• The wavelength of each
light source actually
reaches your
photoreceptors (i.e. not
reflected off a surface).
Additive Mixtures
 Additive Mixtures
• Everyday examples of
additive mixtures
– TV
– Pointillism: small patches
of color (dots) when seen
from a distance seem to
blend together
– Divisionism: interactive
effects of larger patches
of color
Anatomy and Physiology of Color
Vision
Spectral Sensitivity
 Trichromatic Theory
•Color perceived is uniquely determined by relative stimulation of the
three basic retinal receptors (Components).

•M & L cones comprise ~90% of the cones in the retina and randomly
distributed
•S cones comprise ~10% and are fairly regularly distributed
 Trichromatic Theory
• Trichromatic theory of color vision:
– brain interprets the relative amounts of
signaling from each of these cone types
• This means that some colors can be
matched by a pair of wavelengths
– metamers: colors that have no definite single
wavelength (e.g. yellow)
 Trichromatic Theory
• Problem with Trichromatic Theory:
– most people categorize colors into four primaries: red,
yellow, green, and blue

– some colors simply cannot be perceived as gradations of

each other
• redish green !?
• blueish yellow !?

– It is as if these colors are opposites, and cannot explain

afterimages
 Opponent-Process Theory
• Skeptics of the Trichromatic theory argued
that instead of 3 color receptors, there were
three pairs of color receptors
– Each color in these pairs was opposite of the other
(and can not be mixed)
– Red-Green
– Yellow-Blue
– White-Black
 Negative Afterimages

Follow the movement of the rotating pink

dot, you will only see one color, pink. If
you stare at the black + in the centre, the
moving dot turns to green. Now,
concentrate on the black + in the centre of
the picture. After a short period of time,
all the pink dots will slowly disappear, and
you will only see a green dot rotating!
 Opponent-Process Theory
• Red opposes Green
• (Red + Green) opposes
Blue
 Opponent-Process Theory

•Cone photoreceptors are linked

together to form three opposing
color pairs: blue/yellow, red/green,
and black/white.
• Activation of one member of the
pair inhibits activity in the other.
•Opponent-Process Theory
explains color afterimage
Trichromatic Theory or Opponent Theory?
Both theories are needed to explain what is known about
color vision. The trichromatic theory explains color
vision phenomena at the photoreceptor level; the
opponent-process theory explains color vision
phenomena that result from the way in which
photoreceptors are interconnected neurally.
L cone Photoreceptor
Trichromatic output compared in
M cone
Theory higher visual centers
S cone

Excitatory and
L cone Inhibitory firing of
Opponent bipolar cells compared
M cone
Theory in LGN and higher visual
S cone
centers
Individual Differences in Color
Vision
 Color-Vision Deficiencies
• Trichromatic Theory and Opponent-Process Theory
can explain some aspects of color-vision deficiency:
– most of us are trichromats: we have 3 types of
photopigments (S, M, L)
– someone missing one of the three cone types is a
dichromat
– someone missing two is a monochromat
– someone missing all cone types is called a rod
monochromat (very poor vision!)
– anomolous trichromats have less than optimal sensitivity
in one of the photopigments
 Color-Vision Deficiencies
• Genetic factors or disease can eliminate one
or more types of cones
Rod Monochromats
(0.003%) Dichromats
Have B & W vision due to (2% males; 0.4% females)
rods only. Cones do not Unable to distinguish R from
function. G. Also called R-G blindness.

Protanopes 1% Deuteranopes 1% Tritanopes

R-G blind and abnormal R-G blind and abnormal (very rare- 1 in 5-10,000)
insensitivity to long insensitivity to middle Abnormal insensitivity to
wavelengths. wavelengths. short wavelengths.
Color-Vision Deficiencies
 Color-Vision Deficiencies

Responses to Ishihara
Color Plates can
indicate color blindness
 Color-Vision Deficiencies
Normal Vision R-G Blind

L R L R

Top 25 29 Top 25 Spots

Middle 45 56 Middle Spots 56

Bottom 6 8 Bottom Spots Spots

http://www.city.ac.uk/health/research/centre-for-applied-vision-research/a-new-w
eb-based-colour-vision-test
Color-Vision Deficiencies
 Brain Color-Vision Deficiency
• Cerebral achromatopsia: loss of color vision
due to damage to the ventro-medial occipital
cortex
– Have normal vision (can see shapes clearly) but
sees in shades of gray
– If damage is localized in one hemisphere, one half
of their visual field will be in color, the other half
will be black and white
 More than Three Cone Systems
• Many birds have more than 3-cone system
– Can see ultraviolet light
• Some women also have more than 3 cones
– Does not extend the sensitivity spectrum to be
able to see ultraviolet light
– Make more precise discriminations between
colors within the spectrum
 Aging and Color Perception
• One side effect of aging is that the lens tends
to become yellow.
– The wavelengths reaching your retina are changed
– The brain adapts to the change resulting in little
change to the perception of color.
• What would happen if you were to wear
colored lenses?
Color Phenomena
 Color Constancy

• Constancy: your perception of the distal

stimulus remains the same, in spite of changes
in the proximal stimulus.
• Color constancy: using the same color name
for an object despite changes in the
wavelength of the light illuminating the object.
 Color Constancy
• Color constancy
– We perceive the colors
of objects as being
relatively constant
even under changing
illumination.
– A green sweater is
green in sunlight (natual
light) and inside at night
(artificial light).
– Why?

47
 Color Constancy

These images show how a standard daylight film responds to

different illumination. The visual system is able to compensate
color appearances for illumination shifts.
 Color Constancy
• Color perception does not depend on the
absolute wavelengths reaching our retinas
• Color perception depends on reflectance
relationships among objects in our field of
vision

• The color name is constant: does color

appearance remain constant?
 Explanations for Color Constancy
• von Kries: illumination causes adaptive changes
in our photoreceptors (chromatic adaptation)
• Edwin Land: Retinex theory
– Perception of the pattern of reflectances from the
stimuli
– Visual system determines the lightest part of the
stimulus and then determines if that part could be
white (similar to anchor theories of lightness
perception)
 Explanations of Color Constancy
• Early visual experience is necessary for color
constancy.
• Monkeys reared under unusual lighting
conditions: monochromatic light changed every
minute during 12 hour illumination period.
• After 1 year, monkeys were shifted to normal
lighting conditions but could not adjust to the
constantly changing illuminations:
– Could see color
– But had no color constancy
 Simultaneous Color Contrast

http://webexhibits.org/colorart/contrast.html
 Successive Color Contrast

http://www.lifesci.ucsb.edu/~mrowe/SuccessiveColorContrast.html
 Successive Color Contrast
• Chromatic adaptation: your response to a color is
diminished after you view it continuously for a long
time
• Continuous exposure to 1 color may deplete the
photopigments associated with that color, leaving
other photopigment levels relatively high (Re:
Trichromatic Theory)
• Continuous exposure to 1 color may weaken the
response to that color (adaptation), leaving its
opponent strong (Re: Opponent-Process Theory)
Successive Color Contrast
 Subjective Colors
• Color impressions produced by black and white
stimuli (how uncolored figures can produce
subjective color)
• http://lite.bu.edu/vision-flash10/applets/Color/
Benham/Benham.html

• Are the colors produced in the visual system?

• Or are they produced by the white light
breaking into its component colors?
• Color photograph of spinning disc is gray.
 Purkinje Shift
• Our sensitivity to wavelengths shifts toward the shorter
wavelengths as we change from photopic (cone) to scotopic (rod)
conditions.
• Mesopic conditions (middle): when light is sufficiently bright that
cones are still functional, but sufficiently dim that rods can also
function.
 Purkinje Shift

http://psychthecore.wordpress.com/why-oh-why-
are-fire-engines-painted-red/
 Memory Color
• Imagining colorful objects activates areas of the
brain involved in processing color
• Violation of color expectations (that bananas are
yellow) affects the flavor of foods
• Memory color: an object’s usual color influences
your perception of that object’s actual color (e.g. an
apple may appear to be redder than it actually is)
• Knowledge and expectations can shape our
perceptions.
Color Names and Color Perception
• When we categorize things we are attributing
membership based on characteristics shared by group
members (e.g. vegetables, fruits, meats) even though
members within groups have obvious differences.
• When we categorize colors as belonging to “blue” we
perceive these colors having more in common with
blue than with related color green.
• Is this because we have a word for blue and a word
for green?
• Do we perceive the differences between blue and
green because we have a word for these two colors?
Color Names and Color Perception
 Trichromatic Theory
•Color perceived is uniquely determined by relative stimulation of the
three basic retinal receptors (Components).

•Explains positive afterimages and R-G color blindness.

•Drawbacks: Color constancy, lightness constancy, and negative
afterimages cannot be explained.
 Auditory Perception

Chapter 9
Auditory Stimulus
The Auditory System
Hearing Impairments and Treatments
The Auditory Stimulus
 The Auditory Stimulus
• Waves: periodic disturbances that travel
through a medium (e.g. air or water)
• Transport energy
• “What is a Wave?” Dan Russell,
http://www.acs.psu.edu/drussell/Demos/waves-intro/waves-intro.html

l
 The Auditory Stimulus
• A longitudinal, mechanical wave
– caused by a vibrating source
• Pack molecules at different densities
– cause small changes in pressure
 The Auditory Stimulus

https://www.youtube.com/watch?v=g8GcMn7K0u4
http://www.youtube.com/watch?v=2CJJ6FrfuGU
The Auditory Stimulus
 The Auditory Stimulus
• Pure Tones - simple waves
• Complex Tones- tones that cannot be
represented by one simple sine wave
• Harmonics - complex waves consisting of
combinations of pure tones (Fourier analysis) -
the quality of tone or its timbre (i.e. the
difference between a given note on a trumpet
and the same note on a violin) is given by the
harmonics
The Auditory Stimulus
 The Auditory Stimulus
• Wavelength
– distance between peaks
• Frequency
– cycles per second
– relates to pitch
• Amplitude
– height of a cycle
– relates to loudness
• Phase Angle
– Position of the pressure
change as it moves through
one complete cycle Sound is repetitive changes
• Most sounds mix many in air pressure over time
frequencies & amplitudes
 Frequency
• Sound waves are described in terms of
frequency: the number of cycles that a sound
wave completes in 1 second.
• Shorter wavelengths have higher frequencies
because more waves can occur in each
second.
• Relates to the perceptual experience of pitch
(though not perfectly).
 Frequency
• Range of hearing frequencies 20 Hz to 20,000
Hz
• Most sensitive to frequencies from 1000-4000
Hz
– Very sensitive to difference in frequencies within
this range
– Less sensitive to differences between 2 low
frequencies and differences between 2 high
frequencies
 Amplitude
• Amplitude: maximum pressure change from
normal.
• Corresponds to the perceptual experience of
loudness
• High-amplitude sound waves displaces your
eardrum more than a low-amplitude sound
waves
• http://www.skidmore.edu/~hfoley/Perc9.htm
#ch9demo1
 Decibel Scale
• Scale of sound pressures relative to the threshold
pressure (SPL: sound-pressure level) measured in
decibels
• Describes intensity relative to threshold of hearing
based on multiples of 10
– 0 dB = threshold of hearing (TOH)
– 10 dB = 10 times more intense than TOH
– 20 dB = 100 times more intense than TOH
– 30 dB = 1000 times more intense than TOH

• An increase in 10 dB means that the intensity of the

sound increases by a factor of 10
Decibels of Everyday Sounds
Sound Decibels
Rustling leaves 10
Whisper 20
Ambient office noise 45
Conversation 60
Auto traffic 100
Concert 120
Jet motor 140
Spacecraft launch 180
 Phase Angle
• Phase angle is the angle in degrees at each
phase or position of the wave cycle.
• 0° represents normal air pressure just before
the air pressure begins to increase
• 180°- wave returns to normal pressure on its
way to less-than-normal pressure
• 90°- maximum pressure
• 270°- maximum pressure
Phase Angle
Phase Angle
The Auditory System
The Auditory Stimulus
 The Outer Ear

• The outer ear includes the pinna, the

structure of flesh and cartilage attached to
each side of the head
• Responsible for:
– Altering the reflection of sound waves into the
middle ear from the outer ear
– Helps us to locate the source of a sound
 The Middle Ear

• The middle ear contains the tympanic

membrane, which vibrates at the same rate
when struck by sound waves
– Also known as the ear drum
• Connects to three tiny bones (malleus, incus, &
stapes) that transform waves into stronger
waves to the oval window
• Oval window is a membrane in the inner ear
– Transmits waves through the viscous fluid of the
inner ear
 The Inner Ear
• The inner ear contains a snail shaped
structure called the cochlea
– Contains three fluid-filled tunnels (scala
vestibuli, scala media, & the scala tympani)
• Hair cells are auditory receptors that lie
between the basilar membrane and the
tectorial membrane in the cochlea
– When displaced by vibrations in the fluid of the
cochlea, they excite the cells of the auditory
nerve
– http://www.youtube.com/watch?v=G7F_Wl2rV0
Inner Ear
 The Auditory Cortex

• The primary auditory cortex (area A1) is the

destination for most information from the
auditory system
– Located in the superior temporal cortex
• Each hemisphere receives most of its
information from the opposite ear
 The Auditory Cortex

• Organization of the auditory cortex parallels

that of the visual cortex
– Superior temporal cortex contains area MT
• Allows detection of the motion of sound
– Area A1 is important for auditory imagery
– Requires experience to develop properly
• Axons leading from the auditory cortex develop less
in people deaf since birth
 The Auditory Cortex

• The cortex is necessary for the advanced

processing of hearing
– Damage to A1 does not necessarily cause deafness
unless damage extends to the subcortical areas
• The auditory cortex provides a tonotopic map
in which cells in the primary auditory cortex
are more responsive to preferred tones
– Some cells respond better to complex sounds than
pure tones
Hearing Impairments and
Treatments
 Hearing Impairments
• The most common hearing disorders are those that
affect hearing sensitivity. When a sound is
presented to a listener with a hearing sensitivity
disorder, one of two things may occur:
1. The listener with a hearing sensitivity
impairment may be unable to detect the sound.
2. The sound will not be as loud to that listener as it
would be to a listener with normal hearing.
 Hearing Impairments
• Acuity: in vision it is the ability to see fine detail; in
hearing it is the ability to distinguish among differences in
sound
–Vision: common vision disorders affect acuity, not sensitivity to
light. Eyeglasses and contact lenses improve acuity, not sensitivity
to light.
–Hearing: aids improve sensitivity to sound by amplifying sounds,
but do not improve acuity.
–Important: This sensitivity vs. acuity distinction is not quite so
simple with hearing: hearing loss of any significance nearly
always involves problems of both sensitivity and acuity – sounds
are harder to hear (sensitivity) and they are nearly always
distorted (acuity).
 Audiogram
Threshold: Intensity required to barely detect a sound.

Audiogram of a Listener with

Thresholds in the Normal Range
125 250 500 1000 2000 4000 8000
-10
0
10
20
Intensity (dB HL)

30
40
50
60
70
80
90
100
110

Frequency (Hz)
Mild High-frequency Loss
Audiogram of a Listener with a
Mild High-Frequency Hearing Loss
125 250 500 1000 2000 4000 8000
-10
0
10
20
Intensity (dB HL)

30
40
50
60
70
80
90
100
110

Frequency (Hz)
 Moderate-to-Profound Bilateral Loss
Severe Loss Left, Ear Moderate Loss Right Ear
125 250 500 1000 2000 4000 8000

-10

10

20

30
Intensity (dB HL)

40

50

60

70

80

90

100

110

Frequency (Hz)

Average thresholds at 500, 1000, 2000 Hz – the frequencies most

important for speech understanding.
Pure-tone Average, Left Ear: 93 dB
Pure-tone Average, Right Ear: 50 dB
 Hearing Impairments
Normal Hearing: PTAs < 25 dB
Hearing Impairment: PTAs 25-92 dB
Deaf: PTAs > 92 dB
The term deafness is reserved for cases in which “ … the
handicap for hearing everyday speech … [is] … total” (Davis
& Silverman, 1979).
(1) there is no sharp dividing line between hearing
impairment and deafness,
(2) degrees of deafness are meaningful; e.g., there is an
important difference between PTAs of 110 and 95.
 Hearing Impairments
Presbycusis
• Hearing loss associated with aging
• Most common cause of SN HL – and most
common cause of hearing loss overall
• Presbycusis begins in adolescence.
Hearing Impairments
Men

High frequencies are more strongly

affected than lows. (We’ll see this again
when we talk about noise-induced HL.)
Any guesses about why high-
frequencies are more vulnerable?

Women
 Hearing Impairments

• Two categories of hearing impairment

include:
– Conductive or middle ear deafness
– Nerve deafness or inner ear deafness
 Hearing Impairments

• Conductive/middle ear deafness occurs if bones

of the middle ear fail to transmit sound waves
properly to the cochlea
• Caused by disease, infections, or tumerous bone
growth
• Can be corrected by surgery or hearing aids that
amplify the stimulus
• Normal cochlea and normal auditory nerve
allows people to hear their own voice clearly
 Hearing Impairments

• Nerve or inner-ear deafness results from

damage to the cochlea, the hair cells, or the
auditory nerve
• Can vary in degree
• Can be confined to one part of the cochlea
– People can hear only certain frequencies
• Can be inherited or caused by prenatal
problems or early childhood disorders
 Exposure to Loud Noise

Spring 2006 IEOR 170 107

 Hearing Impairments

• Tinnitus is a frequent or constant ringing in

the ears
– Experienced by many people with nerve
deafness
• Sometimes occurs after damage to the
cochlea
– Axons representing other part of the body
innervate parts of the brain previously
responsive to sound
– Similar to the mechanisms of phantom limb
 Hearing Impairments
•Presbycusis:
(1)The sensory-neural component may not be due exclusively to hair cell
loss. Changes in the elasticity of the basilar membrane and metabolic
changes in the stria vascularis may also play a role (Davis, H. and Silverman, S.,
1978, Hearing and Deafness, New York: Holt, Rinehart & Winston ).

(2)There may also be a conductive component due to age-related changes

in the mobility of tissues in the middle ear.
(3)There is sometimes a central component due to the loss of neurons in
the CNS, (related primarily to arteriosclerosis). The result of this CNS
damage is a reduction in acuity and speech perception abilities. The
resulting deficit in speech perception ability is sometimes referred to as
phonemic regression. In some cases it is this problem rather than a loss of
hearing sensitivity that is the patient’s primary complaint.
 Hearing Response Paper
• Go to:
http://www.dailymail.co.uk/sciencetech/article-2643864/Ho
w-good-YOUR-hearing-Video-reveals-frequencies-hear.html
• Read through the description and listen to the
demonstration. Then have someone younger than you and
someone older than you listen to the demonstration and
indicate when they first start hearing the tone and when
they can no longer hear the tone.
• Write about your experience and what you discovered when
others listened to the demonstration.
• What does this tell you about the auditory system and
aging? Why does this happen (physiologically) and can
anything be done to prevent it (behaviorally &
Basic Auditory Functions

Chapter 10
Pitch Perception
Loudness Perception
Auditory Localization
Perception of Simultaneous Sounds
 Physical Dimensions
• Amplitude
– height of a cycle
– relates to loudness
• Timbre
– Complexity of the tone
– Relates to sound quality
• Frequency
– cycles per second
– relates to pitch Sound is repetitive changes
• Most sounds mix many in air pressure over time
frequencies & amplitudes
 Perceptual Dimensions
• Pitch
– higher frequencies perceived as higher pitch
– humans hear sounds in 20 Hz to 20,000 Hz range

• Loudness
– higher amplitude results in louder sounds
– measured in decibels (db), 0 db represents hearing
threshold
 Perceptual Dimensions
• Pitch (not fundamental frequency)
• Loudness (not intensity)
• Timbre (not spectrum envelope or amplitude
envelope)
• The terms pitch, loudness, and timbre refer not to
the physical characteristics of sound, but to the
mental experiences that occur in the minds of
listeners.
 Pitch Perception

• Pitch perception theories include the following:

• Place theory: each area along the basilar
membrane responds to only one specific
frequency of sound wave
• Temporal theory: the basilar membrane
vibrates in synchrony with the sound and
causes auditory nerve axons to produce action
potentials at the same frequency
 Developments in Place Theory
• Waves move down basilar membrane
– stimulation increases, peaks, and quickly tapers
– location of peak depends on frequency of the sound, lower
frequencies being further away

Stapes (base) Helicotrema(ape

x)
 Developments in Place Theory

Stapes Helicotrema

• Envelope of the traveling wave: movement of the basilar

membrane in response to sound waves and where the
displacement peaks depends on the frequency of the stimulus
• Relates to activity of hair cells (stereocilia): stereocilia will be bent
the most at areas of greatest displacement
 Helicotrema (apex)

Stapes (base)
 Developments in Place Theory
• Stimulation Deafness: illustrates the differential
effects of frequency on the basilar membrane.
• Delicate stereocilia are damaged by loud tones
• Loud low-frequency tone damages stereocilia
near the helicotrema (apex) and the damage
extends over a wide area
• Loud high-frequency tone damages stereocilia
near the stapes (base) and the damage is
narrow.
 Developments in Place Theory
• Auditory tuning
curve: represents the
activity of an auditory
neuron when tones
of particular
frequencies are
played
• X-Axis: frequency
• Y-Axis: amplitude
 Complex Waves and Timbre
• Our everyday experience is rich with complex
waves
• Any complex wave can be broken down into
constituent pure sine waves (Fourier Analysis)
 Complex Waves and Timbre
• Harmonics: pure sine-wave components of the
complex sound
• Fundamental frequency (first harmonic): component
of a complex tone that has the lowest frequency and
typically contributes the greatest amplitude
• Overtones: other harmonics of a complex tone that
contribute to timbre, a tone’s sound quality related to
physical quality of complexity

• 200 Hz, 400 Hz, 600 Hz, 800 Hz

• http://www.youtube.com/watch?v=yYf9ij7S5Zs
 Pitch and Fundamental Frequency
All else being equal, the higher the F0, the higher the perceived pitch.

Lower F0, lower pitch Higher F0, higher pitch

 Complex Waves and the Problem of the
Missing Fundamental
• Combine individual pure tones: 400 Hz, 600 Hz, 800 Hz,
1000 Hz to create a complex sound
• What pitch would you say you hear?
• The Missing Fundamental: a complex sound in which
the upper harmonics are present but the fundamental
frequency is absent
• Like illusory contours, with sufficient context the
auditory system can hear a tone that is not physically
there.
• https://www.youtube.com/watch?v=AZ8qZCGg4Bk&t=2
5s
• You can try it yourself!
Developments in Temporal Theory
• Periodic stimulation of membrane matches
frequency of sound
– one electrical impulse at every peak
– maps time differences of pulses to pitch

• Firing rate of neurons far below frequencies

that a person can hear
– Volley principle: groups of neurons fire in well-
coordinated sequence
Developments in Temporal Theory
• Volley principle: auditory nerve as a whole
produces volleys of impulses (for sounds up
to about 4,000 per second)
– No individual axon solely approaches that
frequency
– Requires auditory cells to precisely time their
responses
• Hearing of higher frequencies not well
understood
 Pitch Perception

• The current pitch theory combines

modified versions of both the place theory
and frequency theory:

– Low frequency sounds best explained by the

temporal theory
– High frequency sounds best explained by place
theory
 Pitch Perception
The ear is more sensitive to F0 differences in the low frequencies
than the higher frequencies. This means that:

300 vs. 350 ¹ 3000 vs. 3050

That is, the difference in perceived pitch (not F0) between 300
and 350 Hz is NOT the same as the difference in pitch between
3000 and 3050 Hz, even though the physical differences in F0 are
the same.

300-350: 3000-3050:
 Pitch Perception
• Experience alters our perception of pitch
– Musicians vs. non-musicians
– Blind vs. sighted individuals
• The same physical stimulus, frequency, can lead
to slightly different perceptions of pitch,
depending on experience.
• You can combine different overtones to
produce the same perception of pitch
• The onset/offset of overtones can influence
your perception of a complex tone
Measuring Pitch
•Tone height: A sound
quality whereby a
sound is heard to be
of higher or lower
pitch; monotonically
related to frequency
•Tone chroma: A
sound quality shared
by tones that have
the same octave
interval
Loudness Perception
 Loudness Perception

Higher intensity, higher loudness Lower intensity, lower loudness

 Loudness Perception
• All else being equal, the higher the intensity,
the greater the loudness.
• Adaptation to loudness: listening to the same
continuous tone seems to decrease in
loudness over time
• A sound will appear to be louder after a period
of “rest”
 Loudness Perception
Loudness is strongly affected by the frequency of the
signal. If intensity is held constant, a mid-frequency
signal (in the range from ~1000-4000 Hz) will be louder
than lower or higher frequency signals.

125 Hz, 3000 Hz, 8000 Hz

The 3000 Hz signal should appear louder than the 125

or the 8000 signal, despite the fact that their intensities
are equal.
Loudness Perception
 Loudness and Pitch
• More sensitive to loudness at mid frequencies
than at other frequencies
– intermediate frequencies at [500hz, 5000hz]

• Perceived loudness of a sound changes based

on the frequency of that sound
– basilar membrane reacts more to intermediate
frequencies than other frequencies
Auditory Localization
 Localizing Sounds
• When we perceive a sound, we often
simultaneously perceive the location of that
sound.
• Even newborns orient toward sound sources.
• Interestingly, a given sound contains
absolutely no physical property that
designates its location.
• So the ability to localize a sound must be
caused entirely by neural events, since we
can’t “pick-up” positional cues from the
stimulus itself.
 Localizing Sound
• 3 different coordinates
– The horizontal (azimuth) X coordinate
– The vertical (elevation) Y coordinate
– The distance Z coordinate

ch 12 141
ch 12 142
 Localizing Sound
• On average, people can localize sounds
– Directly in front of them most accurately
– To the sides and behind their heads least
accurately.
– In the horizontal plane better than the vertical
plane
• Location cues are not contained in the
receptor cells like on the retina in vision; thus,
location for sounds must be calculated.
 Cues for Localizing Sound
• Binaural cues - location cues based on the
comparison of the signals received by the left
and right ears
• Identifies sound source in the horizontal
coordinate
– Interaural time difference (ITD)
– Interaural intensity different (IID)
 Cues for Localizing Sound
• Interaural time differences
– Capture the difference in the time that a sound
reaches the left and right ears
– When distance to each ear is the same, there are
no differences in time (in front/behind)
– When the source is to the side of the observer, the
times will differ (left/right)
– Identified by phase differences
Figure 12.4 The principle behind interaural time difference (ITD). The tone directly in front of the listener, at
A, reaches the left and the right ears at the same time. However, when the tone is off to the side, at B, it
reaches the listener’s right before it reaches the left ear.
 Cues for Localizing Sound
– Interaural level difference (ILD)- difference in
sound pressure level reaching the two ears
– Interaural level differences
• Capture the difference in the level of the sound
intensity (sound pressure level) that a sound reaches
the left and right ears
• Reduction in intensity occurs for high frequency sounds
for the far ear.
– The head casts an acoustic shadow.
• This effect doesn’t occur for low frequency sounds.
Figure 12.5. Why interaural level difference (ILD) occurs for high frequencies but not for low frequencies. (a)
When water ripples are small compared to an object, such as this boat, they are stopped by the object. (b)
The spaces between high-frequency sound waves is small compared to the head. The head interferes with
the sound waves, creating an acoustic shadow on the other side of the head. (c) The same ripples are large
compared to the single cattail, so they are unaffected by it. (d) The spacing between low-frequency sound
waves is large compared to the person’s head, so the sound is unaffected by the head.
The three curves indicate interaural level difference (ILD) as a function of frequency for three different sound
source locations. Note that the difference in ILD for different locations is higher at high frequencies (Adapted
from Hartmann, 1999).
 Cues for Localizing Sounds
• Humans localize high frequency sound by
intensity differences (sound shadow) and low
frequency sound by time differences (phase
difference)
– High-frequency sounds (2000 to 3000Hz) create a
“sound shadow”
– Difference in time of arrival at the two ears most
useful for localizing sounds with sudden onset
– Phase difference between the ears provides cues
to sound localization with frequencies up to 1500
Hz
 Cues for Localizing Sounds
• Sound “bounces” around the pinna before
entering the auditory canal.
• The number and direction of the bounces
depends on the direction from which the sound
originates.
• This is equally true for vertical and horizontal
displacements of sound, so unlike ITDs and IIDs,
the pinnas play a role in vertical localization.
• Clearly, experience is necessary
 Localizing Sounds

Here are two pinnas from two different people.

 Localizing Sounds

Each unique pinna produced unique waveforms

in the auditory canal
 Localizing Sounds
• Apparently, our brains adapt to the sounds
that come from our own pinnae.
• Finally, it seems that monaural cues are
sufficient for vertical localization (via the
pinna), since people can perform vertical
localization equally well in monaural and
binaural conditions.
• We are much better at localizing sounds in the
horizontal plane than the vertical plane.
 Localizing Sounds
• Localization errors can be reduced by moving
one’s head.
• However, head movements usually require a
fairly long time (by neural standards), ~500
msec.
• So, head movements are only helpful in
localizing sounds of relatively long durations.
 Estimating Distance from Sound
• Different sound levels
• Frequency
– atmospheric perspective (vision)
– The quality of sound (frequency) is modified by the
atmosphere.
• Movement parallax
– The nearby sound moves quickly than the far away
sound.
• Direct sound vs. reflected sound
– Nearby sound tend to be direct, distant sound tends to
be indirect
• In actuality, we tend to underestimate distances
based on sound information
(a) When you hear a sound outside, you hear mainly direct sound (path a). (b) When you hear a sound
inside a room, you hear both direct (a) and indirect sound (b, c, and d) that is reflected from the walls, floor,
and ceiling of the room.
 Nonhuman Localizing Abilities

• Echolocation: sending out an auditory signal

and gathering information about the
environment from the returning echoes.
• See with sound?
• http://www.youtube.com/watch?v=qLziFMF4
DHA
Integrating Visual and Auditory Localization

• We rely heavily on visual information to

determine an object’s location in space
• Eg. Hear a voice coming from an actor’s lips
even though the sound is coming from the
speakers
• https://www.youtube.com/watch?v=8jiKcvLAY
u0
Integrating Visual and Auditory Localization

• Visual capture: misperceive a sound as coming

from a likely visual origin
• Evolved to emphasize the input and provide
better information
• http://www.michaelbach.de/ot/mot_bounce/
• McGurk Effect: hearing lips and seeing Voices
• https://www.youtube.com/watch?v=2k8fHR9j
KVM
Figure 12.24 Two conditions in the Sekuler et al. (1999) experiment showing successive positions of two
balls that were presented so they appeared to be moving. (a) No sound condition: the two balls were
perceived to pass each other and continue moving in a straight-line motion. (b) Click added condition:
Observers were likely to see the balls as colliding.
 Noise
• Noise is unwanted sounds that have an
adverse effect.
• People differ in their judgments about noise
• Noise impacts health
– Hearing impairment (intensity levels and duration)
– Chronic noise produces stress, leads to
cardiovascular problems, impairs your ability to
sleep soundly, and impacts your ability to
complete complex cognitive tasks
 Perceptual Dimensions
• Timbre
– complex patterns added to the lowest, or
fundamental, frequency of a sound, referred
to as spectrum envelope
– spectrum envelopes enable us to distinguish
musical instruments

• Multiples of fundamental frequency give

music

• Multiples of unrelated frequencies give

noise
 Decibel Scale
• Describes intensity relative to threshold of hearing based on
multiples of 10
• 0 dB = threshold of hearing (TOH)
• 10 dB = 10 times more intense than TOH
• 20 dB = 100 times more intense than TOH
• 30 dB = 1000 times more intense than TOH

• An increase in 10 dB means that the intensity of the sound

increases by a factor of 10

• If a sound is 10x times more intense than another, then it

has a sound level that is 10*x more decibels than the less
intense sound
Decibels of Everyday Sounds
Sound Decibels
Rustling leaves 10
Whisper 20
Ambient office noise 45
Conversation 60
Auto traffic 100
Concert 120
Jet motor 140
Spacecraft launch 180