Opportunity 3

Mr.I

suffered from cerebral achromatopsia was caused by a cortical injury after a lifetime of experiencing color

cerebral achromatopsia

a loss of color vision caused by damage to the cortex

James Tanaka and Lynn Presnell

demonstrated that individuals were able to recognize appropriately colored objects more rapidly and accurately. knowing the colors of familiar objects helps us recognize these objects

Isaac Newton

White light was a mixture of many colors
Individual colors of the spectrum are not mixtures of other colors

Chromatic colors

Blue, green, red occur when some wavelengths are reflected more than others

Selective reflection

When some wavelengths are reflected more than others

Achromatic colors

white, gray, black, occur when light is reflected equally across the spectrum

selective transmission

means that only some wavelengths pass through the object or substance (lens color on a camera)

transmission curves

plots of the percentage light transmitted at each wavelength

blue

short wavelength

green

medium wavelength

yellow

long and medium wavelength

red

long wavelength

white

long, medium, and short

subtractive color mixture

the creation of colors that occurs when paints of different colors are mixed together

Additive color mixture

the creation of colors that occurs when lights of different colors are superimposed

spectral colors

colors that appear in the visible spectrum

nonspectral colors

Colors that do not appear in the spectrum because they are mixtures of other colors. An example is magenta, which is a mixture of red and blue.

What makes hues appear different

is their variation in the other two dimensions' saturation and value

Saturation

is determined by the amount of white that has been added to a particular

desaturated

hues can take on a faded or wash-out appearance

value

refers to the light-to-dark dimension of color
value decreases as the colors become darker

a color solid

is the way of illustrating the relationship among saturation, hue, and value

How does the visual system create our perception of different colors?

Trichromatic theory

Trichromatic theory

we can receive 3 types of color (red, green, blue)
explains the responses of the cones in the retina

Isaac Newton prism experiment

Argued that each component of the spectrum must stimulate the retina differently in order for us to perceive colors

Thomas Young

Color vision is based on three principal colors and that marks the birth of trichromatic theory of vision

opponent processing theory

the theory that opposing retinal processes enable color vision

Short wavelength pigment (S) maximum absorption at

419 nm

Middle wavelength pigment (M) with maximum absorption at

531 nm

Long wavelength pigment (L) with maximum absorption at

558 nm

Metamerism

phenomenon that occurs when two colors appear to match under one lighting condition, but not when the light changes

Metamers

are when two identical fields in a color-matching experiment

priniciple of univariance

With regard to cones, the principle that absorption of a photon of light results in the same response regardless of the wavelength of the light

Univariance means

that the receptor does not know the wavelength of light has absorbed only the total amount it has absorbed

Monochromats

people with one type of pigment, see in shades of gray
only needs one wavelength to match any color
a very rare hereditary condition
only rods and no functioning cones
true color blindness
poor visual acuity
very sensitive eyes to bright light

Dichromats

A person who has a form of color deficiency.
They can match any wavelength in the spectrum by mixing two other wavelengths.

Trichromats

People who have normal color vision who have 3 types of cones

Edwald Hering

came up with opponent process theory
color vision is caused by opposing responses generated by blue and yellow, and by green and red

opponent process theory of color vision

the theory that receptor cells for color are linked in pairs, working in opposition to each other
explains neural response for cells connected to the cones further in the brain

Color circle

arranges perceptually similar colors next to each other around their perimeter

Difference between color circle and color solid

Color circle leaves out variations in hues saturation and value.

Hering's primary colors

the colors red, yellow, green, and blue in the color circle

Hue Cancellation (Hurvich and Jameson)

Procedure in which a subject is shown a monochromatic reference light and is asked to remove and cancel one of the colors in the reference light by adding a second wavelength

Trichromatic theory describes processes that

take place in the receptors in the retina

Opponent process theory describes the processing that

takes place within opponent neurons within the LGN

The L Cone sends excitatory to a (long cone)

bipolar cell

M cone sends inhibitory input to (medium)

the cell

The idea of an area specialized for Color by Semir Zeki based on his finding that

1. His finding that many neurons in a visual area called V4 responded to color
2. The phenomenon of cerebral achromatopsia (Losing the ability to see color)

Cristina Cavina-Pratesi demonstrated that areas in the human cortex that respond to both color and to other visual qualities by

Showing pictures of irregular objects resembling furry balls to subjects while their brain activity was being measured in an fMRI scanner
The subject's task was to press a button to indicate whether two objects presented one after the other was the same or different

Cristina Cavina-Pratesi found

There were areas that selectively respond to color, shape, and texture
When brain damage causes achromatopsia it causes other effects like prosopagnosia

Two types of opponent neurons in the cortex are

Single opponent neurons and Double opponent neurons

single-opponent neurons

Neurons that increase firing to long wavelengths presented to the center of the receptive field and decrease firing to short wavelengths presented to the surround (or vice versa).

double-opponent neurons

neurons that have receptive fields in which stimulation of one part of the receptive field causes an excitatory response to wavelengths in one area of the spectrum and an inhibitory response to wavelengths in another area of the spectrum, and stimulation of an adjacent part of the receptive field causes the opposite response

monochromatism is a

rare form of color blindness
they usually have no functioning cones; their vision has characteristics of rod vision in both dim and bright lights
only see in white, gray, black

Ishihara Plates

38 colored plates used to test those with red-green color blindness

Unilateral Dichromat

a person with trichromatic vision in one eye and dichromatic vision in the other

Protanopia

affects 1% of males and .02% of females and results in the perception of colors shown below
a protanope is missing the long wavelength pigment (cant see red)

indviduals see short-wavelength as blue
neutral point occurs at 492nm
above neutral point they see yellow

Deuteranopia

affects about 1% of males and .01% of females
they are missing the medium-wavelength pigment. (cant see green)

individuals see short-wavelengths as blue
neutral point occurs at 498nm
above neutral point, they see yellow

Tritanopia

is very rare, affecting .002% of males and .001% of females.
they are missing the short-wavelength pigment.
individuals see short-wavelengths as blue
neutral point occurs at 570 nm
above neutral point, they see red

Anolamous Trichromatism

needs three wavelengths to match any wavelength just as a normal trichromat does. however they mix these wavelengths

Color constancy is

perceiving colors of objects as being relatively constant even under changing illiumination

chromatic adaptation

prolonged exposure to chromatic color

Hermann von Helmholtz

Three different receptor mechanisms are responsible for color vision

Keiji Uchikawa

Tested chromatic adaptation

Behavorial Evidence (Maxwell)

color matching experiments
observers adjusted amounts of three wavelengths in a comparison field to match a test field of one wavelength

Results showed that (color matching)

it is possible to perform the matching task
observers with normal color vision need at least three wavelengths to make the matches
observers with color deficiencies can match colors by using only two wavelengths

Evidence for the Trichromatic Theory

Researchers measured absorption spectra of visual pigments in receptors (1960s).
They found pigments that responded maximally to:
Short wavelengths (419nm)
Medium wavelengths (531nm)
Long wavelengths (558nm)
Later researchers found genetic differences for coding proteins for the three pigments (1980s).

Color perception is based on the response of

the three different types of cones

Cone Responding and Color Perception

color perception is based on the response of the three different types of cones.
responses vary depending on the wavelengths available.
combinations of the responses across all three cone types lead to perception of all colors.
color matching experiments show that colors that are perceptually similar (metamers) can be caused by different physical wavelengths.

Behavorial evidence (hering)

color after images and simulataneous color contrast show the opposing pairings
types of color deficiency are red/green and blue/yellow

The opponent-process theory of color vision (late 1800s)
Opponent process mechanism proposed by Hering

three mechanisms: red/green, blue/yellow, and white/black
the pairs respond in an opposing fashion, such as positively to red and negatively to green
these responses were believed to be the results of chemical reactions in the retina

evidence for opponent process theory

DeValois performing single cell recordings found opponent neurons

opponent neurons

are located in the retina and LGN
respond in an excitatory manner to one end of the spectrum and an inhibitory manner to the other

How opponent responding can be created by three types of receptors

each theory describes physiological mechanisms in the visual system

Color in the cortex

there is no single module for color perception
cortical cells in V1, and V4 respond to some wavelengths or have opponent responses
these cells usually also respond to forms and orientations
cortical cells that respond to color may also respond to white

correct terminology for color blindess

achromotopsia/monochromatism
dichromatism

Ocular albinism

uncontrolled back and forth eye movement
not enough pigment in the eye
eyes dont look in the same direction
reduced vision
issues with optic nerves
sensitivity to bright light

Perceptual system must distinguish between

reflectance edges
edges where the amount of light reflected changes between two surfaces
illumination edges where lighting of two surfaces changes

Information in shadows

System must determine that edge of a shadow is an illumination edge
system takes into account the meaningfulness of objects
penumbra of shadows signals an illumination edge

color is a creation of the nervous system

Physical energy in the environment does not have perceptual qualities.
Light waves are not "colored."
Different nervous systems experience different perceptions.
Honeybees perceive color that is outside human perception.
We cannot tell what color the bee actually "sees."

infant color vision (bornstein)

It is a complex problem to know what an infant really "sees."
Chromatic color
Brightness
Bornstein et al. (1976)
Habituation
Young infants have color vision probably as early as 4 months.

physical definition of sound

pressure changes in the air or other medium

perceptual definition of sound

the experience we have when we hear

Loud speakers produce sound through a process:

the diaphragm of the speaker moves out, pushing air molecules together called condensation
the diaphragm also moves in, pulling the air molecules apart called rarefaction
the cycle of this process created alternating high and low pressure regions that travel through the air

pure tone

occurs when changes in air pressure occur in a pattern described by a mathematical function called a sine wave

frequency

the number of cycles within a given time period
measured in hertz (hz): 1 Hz is one cycle per second
perception of pitch is related to frequency
tone height is the increase in pitch happens when frequency is increased

amplitude

difference in pressure between high and low peaks of wave
perception of amplitude is known as loudness
decibel (dB) is used as a measure of loudness
number of dB= 20 logarithm(p/po)
the decibel scale relates the amplitude of the stimulus with the psychological experience of loudness

periodic tone

a tone in which the waveform repeats

fundamental frequency of a tone

is the repetition rate and is called the first harmonic

Periodic complex tones

consist of a number of pure tones called harmonics
additional harmonics are multiples of the fundamental frequency

higher harmonics

pure tones with frequencies that are whole number multiples of the fundamental frequency

frequency spectra

another way to represent the harmonic components of a complex tone

Bekesy place theory of hearing

frequency of sound is indicated by the place on the organ of Corti that has the highest firing rate

Beseky determined the frequency of sound is indicated by the place on the organ of Corti that has the highest firing rate by

direct observation of basilar membrane in cadavers
building a model of the cochlea using the physical properties of basilar membrane.

tonotopic map

cochlea shows an orderly map of frequencies along its length
base responds best to high frequencies
apex responds best to low frequencies

neural frequency tuning curve

Pure tones are used to determine the threshold for specific frequencies measured at single neurons
Plotting thresholds for frequencies results in tuning curves
Frequency to which the neuron is most sensitive is the characteristic frequency

The cochlea's filtering action is reflected by the following three characteristics of tuning curves

1. Neurons respond best to one frequency
2. each frequency is associated with nerve fibers located at a specific place along the basilar membrane with fibers originating near the apex having low characteristic frequencies (illustrates tonotopic map created by cochlear filtering)
3. the curves become wider at higher frequencies (two nearby high frequencies may activate the same filters)

Characteristic frequency

the frequency to which a particular auditory nerve fiber is most sensitive

place theory

the proposal that the frequency of a sound is indicated by the place along the organ of corti at which nerve firing is the highest. Modern place theory is based on Bekesy's traveling wave theory of hearing