Understanding Psychology (10th Ed)

SENDING THE MESSAGE FROM THE EYE TO THE BRAIN
When light energy strikes the rods and cones, it starts a chain of events that trans-
forms light into neural impulses that can be communicated to the brain. Even before 
retina
The part of the eye that 
converts the electromagnetic energy of 
light to electrical impulses for trans-
mission to the brain.
rods
Thin, cylindrical receptor cells in 
the retina that are highly sensitive to 
light.
cones
Cone-shaped, light-sensitive 
receptor cells in the retina that are 
responsible for sharp focus and color 
perception, particularly in bright light.
Study Alert
Remember that cones relate 
to color vision.
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Module 11 
Vision: Shedding Light on the Eye 
107
the neural message reaches the brain, however, some initial coding of the visual 
information takes place. 
What happens when light energy strikes the retina depends in part on whether 
it encounters a rod or a cone. Rods contain rhodopsin , a complex reddish-purple 
substance whose composition changes chemically when energized by light. The sub-
stance in cone receptors is different, but the principles are similar. Stimulation of the 
nerve cells in the eye triggers a neural response that is transmitted to other nerve 
cells in the retina called bipolar cells and ganglion cells . 
Bipolar cells receive information directly from the rods and cones and commu-
nicate that information to the ganglion cells. The ganglion cells collect and summa-
rize visual information, which is then moved out the back of the eyeball and sent to 
the brain through a bundle of ganglion axons called the
 optic nerve .
Because the opening for the optic nerve passes through the retina, there are no 
rods or cones in the area, and that creates a blind spot. Normally, however, this 
optic nerve
A bundle of ganglion 
axons that carry visual information to 
the brain.
Cornea
Fovea
Lens
Retina
Light waves
Light
waves
Front of eye
Back of eye
Nerve fibers
Ganglion cell
Layer of connecting neurons
Impulses to
optic nerve
Retina
Receptor cells
Bipolar cell
Cone
Rod
FIGURE 3 
The basic cells of the eye. Light entering the eye travels through the ganglion and 
bipolar cells and strikes the light-sensitive rods and cones located at the back of the eye. The 
rods and cones then transmit nerve impulses to the brain via the bipolar and ganglion cells. 
(Source: Shier, Butler, & Lewis, 2000.)
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