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Rods and Cones are two types of photoreceptor cells present in the eye. These both contain light-sensitive proteins (called photopigment), the rod-shaped cells respond to brightness or intensity of light and cone-shaped cells respond to the colour of light, i.e., cone-shaped cells enable us to distinguish between different colours.The rods contain purplish-red protein called the rhodopsin or visual purple, which contains a derivative of Vitamin A.Cones have of 3 typed photopigments that respond to red, green and blue lights 
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Rods Cones Comment More photopigment Less photopigment Slow response: long integration time Fast response: short integration time Temporal integration High amplification Less amplification Single quantum detection in rods (Hecht, Schlaer & Pirenne) Saturating Response (by 6% bleached) Non-saturating response (except S-cones) The rods' response saturates when only a small amount of the pigment is bleached (the absorption of a photon by a pigment molecule is known as bleaching the pigment). Not directionally selective Directionally selective Stiles-Crawford effect (see later this chapter) Highly convergent retinal pathways Less convergent retinal pathways Spatial integration High sensitivity Lower absolute sensitivity Low acuity High acuity Results from degree of spatial integration Achromatic: one type of pigment Chromatic: three types of pigment Color vision results from comparisons between cone responses
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