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Chapter 8

PS262 Chapter 8.docx

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Elizabeth Olds

Motion helps us understand our environment  ability to use motion information to determine what is happening is important function of motion perception  motion perception is essential for our ability to move through environment  optic flow: as a person moves forward, objects move relative to the person in the opposite direction  motion agnosia: loss of ability to perceive motion  a woman with motion agnosia found it difficult to pour tea because the liquid appeared frozen and she could not perceive when the glass was full to know when to stop pouring , she also found it difficult to follow convos because she could not see the movement of people's mouths, people and things would also just suddenly appear and disappear making simple things like crossing a street dangerous Motion Attracts Attention  Attentional Capture: ability of motion to attract attention  mice freeze when a cat is around to avoid "attentional capture" from the cat  our motion relative to objects is constantly adding to the information we have about the objects, observer perceive shapes more rapidly and accurately when an object is moving When Do We Perceive Motion  Real motion: actual motion of an object  illusionary motion: perception of motion when there actually is none  Apparent motion: most studied type of apparent motion, the tyoe of motion perceived in movies and tv shows  Induced motion: motion of one object (usually large) causes a nearby stationary object (smaller) to appear to move e.g. moon is stationary but moving can make it appear that the moon is moving through the clouds  motion aftereffects: occur after viewing a moving stimulus for 30-60s and then viewing a stationary object and it appears to move - Waterfall Illusion: looking at a waterfall and then looking at the rocks and trees beside it and they appear to move upwards Comparing Real and apparent motion  the two motions have a lot in common  Axel Larson showed similarities between perception of real and apparent motion and the brain mechanisms associated  as motion happens the image can stay stationary on the retina so motion perception cannot be explained by considering just what happens in the retina  Gibson: information on perception is "out there" in the environment  optic array: the structure created by the surfaces, textures and contours of the environment  movement of the observer causes changes in the optic array  as someone walks by, portions of the optic array become covered and uncovered casing a "disturbance of the optic array" according to Gibson this disturbance provides info that movement in the environment is occuring  as observer moves everything around them appears to move this is called Global Optic Flow Neural Firing to Motion Across Retina  Aperture Problem: viewing a small portion stimulus can result in misleading info about the direction a stimulus is moving  medial temporal (MT) complex: a nucleus in the dorsal stream which contains a large number of directionally selective neurons  neurons that use information about the end of a moving object to determine its direction of motion are found in the striate cortex Moving Dot Stimulus  William Newsome (1989) used a computer to create moving dot displays in which the direction of motion of individual dots can be varied  coherence was used to indicate the degree to which the dots move in the same direction  when all dots move in random directions coherence = 0%  when all dots are moving in the same direction coherence= 100%  Newsome used this stimuli to determine the relation between monkey's ability to judge the direction in which the dots are moving and the response of neurons in MT complex  found that as coherence increased monkeys judged direction more accurately an
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