visual system - dr. martin shapiro
DESCRIPTION
PPT Slides to accompany Dr. Martin Shapiro's Visual System Lecture for Psychology 36.TRANSCRIPT
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.