PSYC 3040 Color Perception

Where does color come from?

Light / Electromagnetic spectrum

What property of light determines its color?

Wavelength

Adding lights together get us closer to ____

white

How is combining light different than combining light?

Combining lights makes the color lighter by adding wavelengths, combining paint makes the image darker by subtracting wavelengths

T/F: Color helps in identifying objects

TRUE

Segmenting the Scene

Color helps to find things in a scene (EX: berries on a tree)

How many different colors can humans see?

20,000 - 200 million

How many basic colors are needed to generate any possible color?

3

Trichromatic Theory of Color

3 Different pigments in cone receptors, they respond to short (blue), medium (green), and long (red) wavelengths

T/F: We can perceive colors that do not exist in the rainbow

TRUE, we can see purple

Color Metamers

Colors that look the same but have a different spectrum

Monochromat

Person who only needs one wavelength to match any perceived color

perceives in grayscale

Dichromat

Person who needs only two wavelengths to match any color

Protanopia

Missing long-wavelength pigment

Red-Green Color Blind

Deuteranopia

Missing medium-wavelength pigment

Red-Green Color Blind

Tritanopia

Missing short-wavelength pigment

Blue-Yellow Color Blind

Ishihara Plate

Circle of differently colored dots used to diagnose color-blindness

Tetrachromacy

Very rare condition where someone has 4 color pigments instead of 3

Color Metamers for a trichromat are not metamers for a tetrachromat

Opponent-Process Theory

Some neurons are excitatory for Some Colors and Inhibit other colors

Three Mechanisms:
White/Black

Red/Green

Blue/Yellow

Evidence of Opponent-Process Theory

• Subjective experience

• Color afterimages

• Hue cancellation experiments

• Neurophysiological evidence

• Opponent neurons located in

retina and LGN

LGN / Cortical Color Neurons

Center-Surround Receptive Fields & Single Opponent Receptive Fields

V1 / Cortical Color Neurons

Edge & Double-O

T/F: Color is heavily dependent on context

TRUE

Color Constancy

Perception of colors as relatively constant in spite of changing light sources

Brain computes “true” color based on:

Surroundings

Memory of Object’s color

Corrections for unexpected correlations

McCollough Effect

After long exposure to colored horizontal or vertical lines, the lines appear to have the opposite color