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 centerInhibitory 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