The Human Visual System

Short Overview

Terms: LGN, cortex, primary visual cortex, V1

Each half of the visual field goes to a different hemisphere of the brain

Hemifield neglect

Eye

Terms: Retina, fovea

Layers of the retina

Terms: photoreceptors, ganglion cells

Receptors Density - Fovea

Rods and Cones

Image Capture

• Huge dynamic range 10-8 – 10+6 μW/cm2

• Photons: poisson process.

• Noisy at low levels

• For low light: large receptors, slow integration

• Rods/cones, local adaptation,change of amplitude and time constant, motion deblur

Dynamic Range

Visual receptor types

Photo transduction: retinal + opsin

Retina Mosaic

Color Mixing

Neural circuitry of the retina

Center-surround Receptive Fields

Modified from PSY280F

Retina Output: Ganglion Receptive Fields

Visual Areas

Physiological Recording

Recording from a Neuron

Orientation Selectivity

V1: Direction selectivity

Modified from PSY280F

Orientation Map, Optical Recording

Contours and Boundaries (V1, V2)

Rotated Subjective Disk

Neon Spreading

Stimuli tested in V2, V4

Seeing without awareness

OR:

• From pixels to perception

• Large part of the brain

• Much of prior to awareness