Visual Receptors

Located close to the center of the eye. Receives messages from receptors at the back of the eye; send messages to the ganglion cells closer to the center of the eye. 154

The point at which the optic nerve and blood vessels exit through the back of the eye. No receptors are present. 154

The ability to recognize colours despite changes in lighting. 160

• Absence of one or two types of cones, or abnormality of them.
• Most common is red-green colour blindness (8% of men): when long- and medium-wavelength cones have the same photopigment rather than different ones. 162

• Abundant in and near the fovea. They are useful in bright light and essential for colour vision. 
• Rods outnumber cones 20:1, but cones provide about 90% of the brain's input. 156

• "pit", a tiny area specialized for acute vision. 
• Each cone in the fovea connects to a single bipolar cell, which connects to a ganglion cell, which has an axon that reaches into the brain. 155

• Located on top of bipolar cells and closer to the center of the eye. 
• Amacrine cells get input from bipolar cells and refine the input to ganglion cells, allowing more precision. 154

• Activity by a particular nerve always conveys the same kind of information to the brain. 
• Action potentials from the olfactory nerve are always interpreted as odors; AP from the auditory nerve always sounds. 152

The ganglion cells in the fovea. Each is small and only responds to a single cone. 155

Red and green, blue and yellow, black and white are switched. 159

Hering proposed that we perceive colours in terms of opposites. 159

Formed by ganglion cells and exits through the back of the head.

• Chemicals contained within rods and cones that release energy when struck by light.
• Consist of 11-cis-retinal bound to proteins called opsins, which modify the photopigments' sensitivity to different wavelengths of light.
• Energy is released when light converts 11-cis-retinal to all-trans-retinal. 156

Opening in the center of the iris where light enters. 153

The rear surface of the eye, which is lined with visual receptors. 153

We use a combination of retinal data and past experience to make a inference about the color and brightness of an object. 160

Located abundantly in the periphery and respond to faint light. 155

We discriminate among wavelengths by the ratio of activity across the three types of cones. 157

• The part of the world you see.
• In the periphery, cones are so scarce that there's no colour vision.