sensation module 3

What is color?

Color is a psychological property created by perception, not a physical property of objects.

How do objects produce perceived color?

Objects absorb certain wavelengths and reflect others; the reflected wavelength determines perceived color.

What is the visible spectrum range for humans?

Roughly 400 nm (violet) to 700 nm (red).

What do wavelength lengths correspond to?

Short = blue/violet, medium = green/yellow, long = red.

Define hue, saturation, and brightness.

Hue = wavelength, saturation = purity of the color, brightness = intensity of light.

Differentiate chromatic and achromatic light.

Chromatic light is an uneven mix of wavelengths; achromatic light is an even mix producing white, gray, or black.

Explain additive color mixing.

Light sources combine—red, green, and blue produce white light.

Explain subtractive color mixing.

Pigments absorb light—cyan, magenta, and yellow combine to produce black.

State the trichromatic theory of color vision.

Three cone types (S, M, L) respond to short, medium, and long wavelengths to form all colors.

Give the approximate wavelength sensitivity of each cone type

S ≈ 420 nm (blue), M ≈ 530 nm (green), L ≈ 560 nm (red).

Describe opponent-process theory.

Color vision is organized into opposing channels: red–green, blue–yellow, and black–white.

What evidence supports opponent-process theory?

Color afterimages occur because of opponent channel rebound.

How do trichromatic and opponent-process theories work together?

Trichromatic operates at the retinal level; opponent-process occurs in post-receptoral neural coding.

Define color constancy.

Perception of object color remains relatively constant under varying illumination.

Describe the Retinex theory.

The brain compares light ratios across surfaces to achieve color constancy.

Which cortical areas are important for color processing?

Primary visual cortex (V1) and area V4 in the temporal lobe.

Define color contrast.

Perceived color of an area depends on surrounding colors.

Differentiate simultaneous and successive contrast. 

Simultaneous = contrast between neighboring colors; successive = afterimage effects following exposure.

What is synesthesia?

A condition where stimulation in one sensory modality automatically triggers experiences in another.

What are common types of synesthesia?

Grapheme–color (letters or numbers evoke colors) and sound–color (tones evoke colors).

What is the neurological basis of synesthesia?

Cross-activation between neighboring sensory regions such as auditory cortex and area V4 in the temporal lobe.

Define color blindness.

A deficit or loss in one or more cone systems, most often red–green.

How common is color blindness and who is affected most?

About 8 percent of males; it is X-linked and passed through the mother.

List the three dichromat types and what cone system each lacks.

Protanope = missing L cones (red), Deuteranope = missing M cones (green), Tritanope = missing S cones (blue).

What is a trichromat, dichromat, and monochromat?

Trichromat = normal three-cone vision; dichromat = two functional cones; monochromat = one or none.

What tests screen for red–green color blindness?

The Ishihara plates test.

Name two arrangement tests for color discrimination.

Lanthony D-15 and Farnsworth-Munsell 100 Hue tests.

What is an electro-retinogram (ERG)?

An electrophysiological measure of photoreceptor activity in the retina.

What is a visual-evoked potential (VEP)?

A cortical recording from EEG electrodes measuring visual-pathway activity.

What photopigments are missing in protanopes and deuteranopes?

Protanopes lack erythrolabe (L-cone pigment); deuteranopes lack chlorolabe (M-cone pigment).

What is achromatopsia?

A neurological inability to recognize or experience color, usually from cortical damage.

Define metamers.

Physically different light mixtures that are perceived as identical in color.

What device measures metameric matching?

The Nagel anomaloscope.

Describe the Rayleigh Match Test.

Observers mix red and green lights to match a yellow standard to diagnose red–green deficiencies.

How do protan and deutan observers differ in Rayleigh matches?

Protan observers require more red light; deutan observers require more green.

What is metameric matching behavior for trichromats versus dichromats?

Trichromats adjust three primaries; dichromats can match using only two plus brightness adjustment.

What is the approximate number of cone types and how do they combine? 

Three cone systems overlap in sensitivity, and their relative activation determines perceived color.

What is the purpose of additive versus subtractive mixing demonstrations? 

dditive models light mixing; subtractive models pigment absorption.

Where does opponent coding first appear in the visual system?

In ganglion cells and LGN neurons that show excitatory–inhibitory responses.

How does color constancy benefit perception?

Allows stable recognition of objects despite lighting changes.

What causes afterimages?

Adaptation and rebound in opponent-process channels after prolonged stimulation.

What part of the brain is specifically linked to detailed color processing?

Area V4 in the ventral visual pathway.

How is synesthesia studied neurologically?

Through neuroimaging showing overlapping activation of auditory and visual areas.

Besides heredity, what other causes can lead to color deficits?

Retinal disease, optic-nerve injury, or cortical damage.

How can electro-retinograms and VEPs be used clinically?

To assess retinal versus cortical contributions to visual disorders.

What is the relationship between color vision and film or art?

Color use manipulates mood and focus within a scene.

What is an anomalous trichromat?

A person with three cones but one has shifted sensitivity leading to partial color discrimination loss.

How can metamers demonstrate limitations of color matching?

Different wavelength mixtures can appear the same to normal trichromats, revealing perceptual equivalence.

What do monochromats perceive in a metameric test?

They match colors solely by adjusting brightness because they lack hue perception.

What practical purpose do arrangement tests serve?

They measure subtle hue-ordering ability to detect mild color deficiencies.

How are ERG and VEP results interpreted together?

ERG evaluates retinal function; VEP assesses cortical response, helping localize deficits.