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
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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