Visual Processing Processing in the Retina On Center

Visual Processing • Processing in the Retina – On Center and Off Center Cells • Higher Levels of Processing – Neural Pathways – Edge Effects – Motion Illusions – Perceptual Learning and Ambiguity

Optical Processing • Level one processing occurs in the retina, the rods and cones are the first order cells, bipolar cells are 2 nd order and ganglionic cells are third. Amacrine cells and horizontal cells create both converging and diverging pathways. • Rods and cones hyperpolarize when stimulated and Na channels close • Horizontal cells produce graded hyperpolarizations • Some bipolar cells hyperpolarize and some depolarize • Some ganglionic cells hyperpolarize and some depolariize. • Ganglionic cells are matched to their bipolar cells • Amacrine cells respond transiently when the stimulus changes

Each ganglionic cell has a particular area of the retina that it receives information from. These visual fields are circular. The fields near the fovea are quite small so visual acuity is great. The fields are divided into two areas -- a center and a surround. There are two types of fields an on center field an off center field. On Cell Ganglion responds when light in center, inhibited by light in surround Off Center. Inhibited when light in center, fires when light in surround

Film Clip on Processing

• • First order – rods and cones Second – bipolar cells Third – ganglionic cells Fourth – neurons of the lateral geniculate nucleus • Fifth – Simple cells of the visual cortex • Sixth – Complex cells of the cortex (Brodman’s Area 17)

Simple Cell and Motion Illusions