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Movement Perception.docx

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Department
Psychology
Course
PSYC 2390
Professor
Lana Trick
Semester
Fall

Description
Movement Perception 10/29/2012 8:40:00 AM Movement Perception What is motion perception?  Ability to see movement o See objects changing position  One of most important attributes of vision o Can be colour blind and have bad depth perception but still survive because of the ability to see motion Why is motion perception important?  Attracts attention (attentional capture, seeing your friend waving in the crowd, effect occurs when you are consciously looking for something and when you are paying attention to something else) o Important role in survival  Helps us understand our environment  Provides information about objects Motion Defines Object Form and Can Aid in Object Perception: Grouping by common fate (grouping in 2D)  Group together objects that are moving together  Can use this to define form and contours  Random dot kinematograms o Shift square over and see form defined by that movement  One reason that camouflage animals need to freeze in order to be hidden o As long as they are still they are protected  As soon as they start moving, grouping by common fate causes them to be distinguishable Grouping in 3D  Kinetic depth effect o Take wire cube and have projector on cube o If still, shadow will look 2D o As soon as you start spinning cube, shadow will look 3D  Ullman‟s Structure from Motion displays o Involves random dots (salt and pepper diagram of cylinder) o Cylinder inside cylinder o One moves 1 way and the other moves the other  Can see the inside cylinder  Biological motion: Johansson Figures o Our ability to see biological motion o Wear black leotard and have light emitting dials on joints o Put people in dark and when they move, can see and recognize that they are people (when still just looks like random array of lights) o Can distinguish movement that occurs in humans vs. animals just by seeing light emitting dials of joints  Can even tell which is male and which is female  Can tell which is yourself (movement is individual to you) o Cats can tell difference between cats and non cats o Example of how movement can create perceptual organization  Movement transforms dots that appear unrelated into a pattern that is almost immediately seem Motion Agnosia: inability to recognize motion  e.g. cannot fill glass because cannot see where liquid is compared to the top of the glass, first thing you know it is one third from the top, next image is of the glass overflowing  Akinetopsia Motion and Visual Motor Coordination: Motion Defines Depth (Depth Cues from Motion)  Relative motion and motion parallax o Motion can help define depth o Moving forward  Close to you  moves in opposite direction  Accretion and deletion o Deleting things vs. growing things o Causes local disturbance in the optic array o Provides information that object is moving relative to the environment or vice versa (if fixating on object moving, it appears that the environment is moving) Motion and Balance  Optic flow o Lose balance very fast when eyes are closed o Takes lot of training to be able to use vestibular sense for balance (most people use vision to help balance) o Optic flow  image blurring as you move  Visual capture (star wars movie, had vision scientists to try and give illusion that viewers were moving)  Swinging room experiment o Showed importance of optic flow o Conducted with toddlers o Had toddler in room (roof and walls were hanging from chains)  Can move roof and walls back and forth o Made walls of room go back and worth, when walls moving forward (approaching you), optic flow coming forward  Sense of falling forward and toddlers leaned back and fell on butt because didn‟t need to make that adjustment (can‟t help but use visual information in actions) o Made walls flow away from you, interpret as optic flow moving away from you  Sense of falling backwards therefore lean forward and fall on face because of adjustment o Visual capture  visual information is taking over from sense of balance  When senses are in conflict with each other, vision wins even when it is not correct  Motion and projectiles (motion in depth) o Looming  Object gets larger and larger and baby leans back because it thinks object is going to hit them in the face  Change in size over time tells you when you will get hit with the object Apparent vs. Real Motion 1. Apparent motion (illusion)  can have static pictures and if you put them close together in time, will see that object moves  Both objects are static dots but when put close together in time will see them moving  Principle behind flip book  Visual system easily confuses real motion and apparent motion  Induced motion: when motion of one object (normally large) causes a nearby object (usually smaller) to appear to move o Moon is still but clouds moving past moon makes it appear as though the moon is moving Wertheimer (Gestalt psychologist)  30ms between images, see both images on same display  between 60-200ms between images, see movement o TV and movies  200ms+ will just see two static pictures Motion Aftereffects  After viewing a moving stimulus for 30-60 seconds and then viewing a stationary stimulus, which appears to move  E.g. waterfall illusion o Flows down, look at stationary, appears to move up 2. Real motion  motion happening in real time  Brain areas involved in real motion are also activated during apparent motion Physiological Mechanisms of Motion Perception 10/29/2012 8:40:00 AM Physiological Mechanisms of Motion Perception Two Systems: Image Retina System  Requires things to move on retina (must change position on retina in order to see movement)  Illusions are often based on image retina system  E.g. waterfall illusion o Look at waterfall for long period of time, eyes still, look away and see motion in opposite direction (guitar hero) o If try tracking object with eye will not get after image as well Eye-Head system  Incorporates eye and head movements  Can still see object moving even if it stays on same position of eye (e.g. fovea)  Tracking object with eyes / head, stays on same position on retina but still see object as moving Aubert-Fleischl Effect  Eye head and image retina system can both determine how fast something moves but does not always conclude same speed  Track pendulum with eyes and get idea of speed  Then look at pendulum keeping eyes still o Appears to be moving faster when eyes are still (image retina system thinks object moves faster than what eye head system says)  Image retina system is more accurate o Eye head system uses eye movements (eye muscles) to judge speed (sometimes eyes cannot keep up with speed of object) Image Retina System: How do neurons signal motion? (Reichardt Motion Detectors):  See loose leaf paper  Stimulus sweeps across retina, activates directionally selective neurons in cortex  Leads to aperture problem: o Pencil example moving right vs. pencil moving up and right (both appear to be moving right)  A single directionally selective neuron would fire similarly in both situations  Movement of edge across aperture occurs perpendicular to direction in which edge is oriented o Viewing only small portion of larger stimulus can result in misleading information  Solution: o Pool our response from number of neurons (MT cortex) o Neuron can also use information about the end of a moving object to determine its direction of motion Neural Firing and Perception of Moving Dot Stimuli  Judge monkey‟s ability to judge direction that dots were moving and measured response of MT cortex o Simultaneously measuring perception and firing of neurons  One display had dots moving in random directions o Coherence at 0%  Second display, 50% of dots were moving in same direction, the rest were random o Coherence at 50%  In third display, all dots moving in same direction o Coherence at 100%  As dot coherence increased, monkeys judged the direction more accurately and the MT neuron fired more rapidly  Can also show effects of MT by lesioning or electrically stimulating it o When lesioned,
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