Visual System - Dr. Martin Shapiro

Vision

Bionic Eye / Artificial retina

Retina

Retina

Rods and Cones

Rods vs. Cones Rods:

Scotopic vision

Night vision Achromatic Peripheral

vision ~130 million

Cones Photopic

visionDaytime vision

Color vision Foveal vision ~ 7 million

Spatial Summation

Transduction of Light

Action Potential

Rod

Transduction

Inside

Outside

cGMP Rhodopsin

Retinal

In the dark

Transduction

Inside

Outside

cGMP Rhodopsin

Retinal

In the light

Transduction summary

In the Dark Opsin and retinal (rhodopsin) are bound

together Rod membrane is depolarized slightly at

-30 mV Na+ constantly moving in – the dark

current. Kept open by cGMP

In the Light A photon of light changes the shape of

retinal causing rhodopsin to break apart.

Causing a reduction in cGMP The rod becomes hyperpolarized.

Visual Pathway

Optic nerve Optic chiasm Superchiasmatic nucleus Lateral geniculate nucleus of the

thalamus Superior colliculus Visual cortex

Visual Pathway

Visual Pathway

Visual Pathway

Thalamus

Thalamus

Striate Cortex

Center-surround receptive fields

On-Center Cell:Response most when light strikes the center.

Off-Center CellResponse most when light strikes the outer portion of the receptive fields.

On-Center Ganglion Cell

Receptive Fields of the Visual Cortex

Hubel and Wiesel: Nobel laureates for medicine and physiology, 1981)

Not circular receptive fields Linear receptive fields

Striate Cortex

Neurons are specialized to respond best to specific aspects of the stimulus: orientation, movement, size, direction.

Record from single cells in the striate cortex and present stimuli to the visual system.

Complex Cortical Cells

Like Simple cells they are orientation specific

Large receptive fieldReact to movement in a specific direction

Inferotemporal cortex

BEV DOOLITTLE

Our Senses

Which is longer and which is wider?

Visual System Summary

Transduction of light information to neural signals at the retina.

Modified at the retina with center-surround fields (intermediate cells).

Signal goes out the ganglion axons to the LGN

Back the Primary visual cortex for building of the image in: serial and parallel processing.

Context and memory play a big role in perception.