Sensation and Perception
• Sensation– a process by which our sensory receptors
and nervous system receive and represent stimulus energy
• Perception– a process of organizing and interpreting
sensory information, enabling us to recognize meaningful objects and events
Figure 6.2 Cross section of the vertebrate eyeNote how an object in the visual field produces an inverted image on the retina.
Eye Structures
Visual Coding and Retinal Receptors
The Eye and Its Connections to the BrainPupil-opening in the center of the eye that allows light to
pass throughLens-focuses the light on the retinaRetina-back surface of the eye that contains the
photoreceptorsThe Fovea-point of central focus on the retinablind spot-the point where the optic nerve leaves the eye
Visual Coding and Retinal Receptors
Transduction-the conversion of physical energy to an electrochemical pattern in the neurons
Coding- one-to-one correspondence between some aspect of the physical stimulus and some aspect of the nervous system activity
Figure 6.4 Visual path within the eyeballThe receptors send their messages to bipolar and horizontal cells, which in turn send messages to the amacrine and ganglion cells. The axons of
the ganglion cells loop together to exit the eye at the blind spot. They form the optic nerve, which continues to the brain.
Optic Nerve Exits
Visual Receptors: Rods and Cones
Rods
abundant in the periphery of the retina
best for low light conditions
see black/white and shades of gray
Cones
abundant around fovea
best for bright light conditions
see color
Night time Day time
Figure 6.18 An illustration of lateral inhibitionDo you see dark diamonds at the “crossroads”?
Lateral Inhibition
Rods at work
Figure 6.18 An illustration of lateral inhibitionDo you see dark diamonds at the “crossroads”?
Lateral Inhibition
Retina to Thalamus
An Overview of Visual System
Rods and Cones synapse to bipolar cells
Bipolar cells synapse to ganglion cells
Axons of the ganglion cells leave the back of the eye
The inside half of the axons of each eye cross over in the optic chiasm
Pass through the lateral geniculate nucleus