Color Vision

Topic 4: Anatomical and Physiological Basis of Color Vision

Happy Valentine!

Outline

• Anatomy of human eye• Retinal Circuitry

Anatomy of Human Eye

http://www.youtube.com/watch?feature=player_detailpage&v=Z8asc2SfFHMb

Retinal Circuitry

Photoreceptors

Rods• 100 million, rich in periphery• Highly sensitive, operating at

dim lights• Poor spatial, temporal vision• Poor color vision

Cones• 8 million, rich in fovea• Less sensitive, operating at

bright light• Good spatial, temporal vision• Good color vision

Photoreceptors

ScotopicRods alone

PhotopicCones alone

MesopicRods & Cones

Stockman & Sharpe 2006, Based on Design of Hood & Finkelstein, 1986

Rod and Cones (Dark-Adaptation Curve)

Rods and Cones (Increment Threshold)

Rods and Cones

Rods and Cones

Rods and Cones

Ganglion Cells

How they do what they do

Ganglion cells receive chemical messages from retinal interneurons which they turn into electrical messages to send to the brain visual centers.

This is done through induced membrane currents, when neurotransmitters start a response of either excitatory or inhibitory ganglion cells

Different Types of Ganglion Cell Types/Responses

ON-cell: respond with impulses to transient bursts of light during the whole time light is being used as a stimulus

OFF-cell: respond with impulses when light is turned off, for the whole time there is no light

Receptive Field

Color Selective Ganglion Cells

• Red ON/Green OFF• Red OFF/Green ON• Green ON/Red OFF• Green OFF/Red ON

Ganglion Cells

Ganglion Cells

Questions• When we are in a pitch black room, and then turn the lights on,

what part of our eye makes our eyes squint? Which part in our eye is the most sensitive to light?

• Is there a way to perceive the blind spot on the retina, or does our brain fill it in with perceptions from the other eye? How big is this blind spot?

• Does the thickness of the central retina contribute to why it does not show as much of the outside world as the peripheral retina?

• Why are the cells in the sensory layer of the retina arranged the way they are? Wouldn't it make more sense to have the rods and cones be closest to the lens since having the light pass through the ganglion and bipolar cells would scatter the light, decreasing the quality of images we see?

Questions

invertebrates vertebrates