Vision is more than what we see.

Karl Lashley

American Psychologist

1890-1958

Memory storage

Migraine Headaches

Migraine alters Vision

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Lashley’s Migraine

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

Perception at Work

Bill or Monica?

Eye as Camera

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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

Visual Spectrum

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Retina

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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

Locating Blindspot

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Rods and Cones

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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

Three Cones = Color Vision

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Afterimages

KW 8-36 Stare a box for 30 seconds

Afterimage a

Afterimages b

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

Convergence

Retinal Circuits

Retinal Layers

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Amacrine Bipolar

(Blue) (Purple)

Visual Pathway

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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

Optic Nerve

to LGN

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Nasal Fibers

Temporal Fibers

LGN

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LGN and Superior Colliculus

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Striate (Primary) Cortex

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Cell Bodies in Striate

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Visual Fields

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Fovea on

Cortex

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