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The Visual System and Brightness

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John Minda

on 22 September 2010

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Transcript of The Visual System and Brightness

The Visual System The Neuron The Eye Sensory, Motor, & Interneurons Visual Pathways The Visual Brain Primary Visual Cortex (occipital pole) VI is organized retinotipcally Simple cell and complex cell Receptive fields Single Cell Recording V1-V5 Area V3 Area V4 Area V5 Form and Local Movement Colour Information from retial image is 'bound" or categorized Global Motion Dorsal System (where) Ventral System (what) Lesion studies: identification but imparied localization Optic Axatia Psychic Blindness Visual Agnosia Specialization superior temporal cortex Radiance: energy coming from a light source Illuminance: light falling on a surface 1 Lumen/m^2 The Visual Stimulus Units Colour stimulus Color Vision Lumen Reflectance:percentage of light falling on a surface Luminance: light reflected from a surface 1 candela = 1 standard candle shown for 1 meter on a square meter (Illiminance * reflectance)
100 Luminance
___________ * 100
ill Retinal Luminance: ammountant of light falling on the retina 1 candella / m^2 seen through pupil of 1 mm^2 area Subjective Impressions brightness :impression of the amount of light emitted lightness : impression of reflected light as a portion of total light "whiteness" Why is it necessary to distinguish between subjective and objective meaures of light and brightness? Photometic Units Light from a direct source vesus light from an indirect source The amount of light from a single "standard candle" Spectral Colours: a single wave length Attributes:
Brightness Additive:
Mixing Light
Each wave adds to the others
The eventual sum is white Subtractive
Mixing paints/solids
each pigment reduced the light being relected back
The eventual sum is dark grey or black Brightness Dark Adaptation Spatial Contex The rapid depolarization of the spike potential is caused by sodium ions flowing into the cell. Visual accommodation-: focusing of the lens through a change in shape. The retina is composed of three neural layers of cells as well as of two types of cells that have lateral connections.

These layers are arranged as follows: rods and cones; horizontal cells; bipolar cells; amacrine cells; ganglion cells. When a molecule of the pigment rhodopsin absorbs light it becomes photopsin.

The end effect on the rod resulting from the absorption of light by the photopigments is a neural action potential. Ways to study Neural Function
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