Color Vision Theory

Question 1

Under the Trichromatic theory what are the colors and pigments associated with the long, medium and short wavelength sensitive cones? (pigments end in -labe)

Are these wavelengths precise?

Answer 1

• Long wavelength: Red, erythrolabe
• Medium wavelength: Green, chlorolabe
• Short wavelength: Blue, cyanolabe

Wavelengths are not precise

Question 2

What is the max absorption wavelength for long, medium and short?

(between 400-600 nm)

Answer 2

• Long: 560 nm
• Medium: 530 nm
• Short: 420 nm

Question 3

What is the ratio of Long, medium and short wavelengths in the central retina?

(Is it the same ratio for fovea?, Which has the fewest number of wavelength receptors? (Long, medium or short)

Answer 3

• Central retina: 40:20:1, long:medium:short
• Fovea has variability in long and medium ratio
• Short wavelength have the fewest receptors

Question 4

Which are FALSE about the Trichromatic Theory? (Pick 2)

A) Color is determine by the magnitude and ratio of stimulation of L, M, S cones
B) Each photoreceptor does not determines color
C) If only one cone present can still descriminate based on wavelength
D) If only one cone present, you can discriminate between stimulus based on intensity and percent absorbed
E) Absorption and Neural effects are both dependent on wavelength

Answer 4

C) and E) are FALSE

Can not descriminate color on the basis of wavelength if only one type of cone present

E) Neural effect is independent of wavelength. response is inside the photoreceptor (hyperpolarization)

Question 5

What two wavelengths are the areas most sensitive to change and which wavelength receptors (L, M, S) are stimulated at those wavelengths?

Answer 5

• 490 nm (L, M, S) are stimulated

- 580 nm (L, M) are stimulated

Question 6

What cells are involved in Trichromatic Theory (Young-Helmholz) and the Opponent Theory? (Hering)

(Trichromatic: one type of cell involves wavelength, Opponent: two cells involves neural transmission along visual pathway)

Answer 6

Trichromatic Theory: Photoreceptors

Opponent Theory: Bipolar, Retinal Ganglion cells

Question 7

What are three opponent neural response channels based on the Opponent Theory? (Two color channels, One luminance channel)

(Opponent Neural Response 1 Portion Excitation, One portion inhibition)

Answer 7

B-Y (Blue-Yellow) color channel
R-G (Red-Green) color channel
B-W (Blue-White) luminance channel (for brightness)

Question 8

What two color combinations are never seen simultaneous according to the Opponent theory?

Answer 8

• Red-Green

- Blue-Yellow

Question 9

What are the signals organized in the Opponent Theory to form final color perception?

(What happens to the R-G, B-Y signals? Is there a Color Mixing?)

Answer 9

• Final color perception is a combination of R-G and Y-B opponent channels
• There is no color mixing at this stage. Purely a neural reponse

Question 10

Describe the B-Y opponent color channel and what color appears with more long/medium, short and balanced wavelengths.

(What wavelength receptors it recieves stimulation from, does it recieve input from an intermediate channel)

Answer 10

• Recieves stimulation from long, medium and short wavelength
• long and medium wavelengths input into an intermediate channel (Yellow)
• Stimulate more long, medium wavelengths will look yellow
• Stimulate more short wavelength will look blue
• Stimulate balanced wavelength will look white

Question 11

Which cone photoreceptors contribute to brightness perception?

A. Long
B. Medium
C. Short
D. All of the above

Answer 11

D. All of the above

Question 12

Interactions between medium and long wavelengths in the cone is completely a neural response. (i.e. No color addition/subtraction) TRUE/FALSE?

Answer 12

TRUE

Question 13

What lateral connections cells are found in the outer and inner retina and what do those cells connect?

(Think of the cells in the 9 layers of the retina and signal inhibition cells in Vision Science)

Answer 13

• Outer retina: Horizontal cells. Connect cones and bipolar

- Inner retina: Amarcrine cells. Connect bipolar and ganglion

Question 14

What role does the magnocellular visual pathway play in color vision?

A. Luminance
B. Red-Green
C. Blue-Yellow
D. Recieves information from midget ganglion cells (cones)
E. Has opponent cells

Answer 14

A. Luminance

Magnocellular has no role in color perception

Question 15

What role does the parvocellular visual pathway play in color vision? (Pick 3)

A. Luminance
B. Red-Green
C. Blue-Yellow
D. Receives information from midget ganglion cells (cones)
E. Has opponent cells

Answer 15

B. Red-Green
D. Receives information from midget ganglion cells (cones)
E. Has opponent cells

Question 16

What role does the konio (small bistratified) gangion cells play in color vision? (Pick 2)

A. Luminance
B. Red-Green
C. Blue-Yellow
D. Receives information from midget ganglion cells (cones)
E. Has opponent cells

Answer 16

C. Blue-Yellow

E. Has opponent cells

Question 17

Where in the neural system does color vision occur?

Which part of the brain?

Answer 17

• Primary Visual Cortex (Striate Cortex and V1)

Question 18

What is cerebral chromatopsia?

How does it occur, which part of the brain it affects, what is affected

Answer 18

• Stroke damage near calcarine sulcus
• affects color perception
• without cerebral function, no color vision