Decrease in sensitivity of a receptor to a stimulus

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– decrease in sensitivity of a receptor to a stimulus after constant stimulation With vision, we are actually seeing light bounce off an object and into our eye o Light enters eyes through pupil – tiny opening behind the cornea o Pupil regulates amount of light entering by contracting (smaller) in bright light & dilating (bigger) in dim light o Light will pass through a lens – focuses an image on thin layer of cells in back of eye ( retina ) Image focused on each retina is from a slightly different angle since we have 2 eyes o Binocular disparity – difference in images processed by left and right eyes o This binocular disparity provides us w/ our perception of 3D space Binocular vision – ability to perceive 3D and depth due to difference btwn images on each retina
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o Perception of 3D w/o glasses is created by 2 slightly different images presented on top of one another Light is converted into electrical signals ( transduced ) in retina by photoreceptors – rods and cones o Rods – cell layer in back of eye containing photoreceptors, responsibly for ability to see in dim light o Cones – photoreceptor of retina sensitive to color, primarily in fovea Rods and cones differ in distribution across retina o Cones are mainly found in the fovea – central region of focus o Rods are mainly found in the periphery Electrical signal is sent through a layer of cells in the retina that eventually travel down optic nerve o Signal passes through thalamus and makes it to the primary visual cortex Primary visual cortex – area of cortex involved in processing visual stimuli o Info is sent to a variety of different areas in the cortex for more complex processing Fusiform face area – processes faces, Extrastriate body area – processes body parts o Damage to areas of cortex can result in agnosia – lost of ability to perceive visual stimuli Prosopagnosia – inability to recognize face Specialized regions for visual recognition make up the ventral pathway (“what” pathway) while areas involved in processing location and movement make up the dorsal pathway (“where” pathway) o Ventral pathway – pathway of visual processing, “what” pathway o Dorsal pathway – pathway of visual processing, “where” pathway Humans have the ability to adapt to changes in light conditions o Dark adaptation – adjustment of eye to lower levels of light Night vision takes time to turn on – rods bleached in normal light conditions & need to recover o Light adaptation – adjustment of eye to high levels of light Happens almost instantly – lots of rods and cones are bleached at one, blinded for a few seconds o Use red light to turn on a light without losing night vision – red light doesn’t bleach rods We have cones that respond preferentially for red, green, blue o Trichromatic theory – theory hat color vision is influenced by 3 different cones (RGB) Doesn’t explain odd effect that occurs when we look at while wall after staring at a picture You end up seeing an afterimage which is not explained by trichromatic theory o Opponent-process theory – theory that color vision as influenced by cells responsive to pairs of colors
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