Transcript No Slide Title

Visual Processing
• Structure of the Retina
• Lateral Inhibition
• Receptive Fields
Structure of the Retina
• Photoreceptors
– Horizontal cells
• Bipolar cells
– Amacrine cells
• Ganglion cells
Optic Nerve
• Ganglion cells produce the first action
potentials in visual system
• Ganglion cell axons make up optic nerve
• Area where optic nerve exits the retina is
the optic disc, which creates a blind spot
because there are no photoreceptors there
Lateral Inhibition
• Connecting cells in the retina inhibit
neighboring cells
• This results in heightened perception of
edges
Mach Bands
Receptive Fields
• The receptive field is the area in the
environment to which a neuron responds
• Ganglion cells have center-surround receptive
fields:
– excitatory center/inhibitory surround
– inhibitory center/excitatory surround
Excitatory center
Inhibitory Center
The Lateral Geniculate Nucleus
• Ganglion cells synapse in Lateral Geniculate
Nucleus (LGN) of thalamus
• LGN cells also have center-surround
receptive fields
• Retinotopic organization
Striate Cortex (V1)
• Retinotopic organization
• Over-representation of foveas
• Types of cells:
– Simple
– Complex
– End-stopped
Simple Cells
• Respond to lines
• Specific orientation and location
Complex Cells
• Respond to moving lines
• Specific to orientation
• May be specific to direction of movement
End-Stopped Cells
• Respond to lines of specific length
• May respond only to corners or angles