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Prof. Greg Francis1PSY 310: Sensory and Perceptual ProcessesPurdue UniversityMotion perceptionPSY 310Greg FrancisLecture 23Where would you grab this branch?Purdue UniversityMotion and survival Almost all animals with vision are very sensitive to motion Motion contributes to object perception and figure-groundidentification Camouflaged objects become visible with motion (Hidden item) Small details in motion dramatically change figure-groundrelationships (Moving rings) Object properties vary with motion (Teapot) Like everything else in sensation and perception Our percepts of motion generally track some importantcharacteristics of things in the real world However, the percepts are based on certain computations ofvisual information and do not always correspond to true motionProf. Greg Francis2PSY 310: Sensory and Perceptual ProcessesPurdue UniversityTypes of motion Our textbook describes four ways of producing amotion percept There are actually many more Real movement Apparent movement Induced movement Motion aftereffectPurdue UniversityReal motion For a physical object to get from one place toanother, it must cover some path in between We do not detect all movements Some things move too fast Light Blurs Some things move too slow Hour hand of a clockProf. Greg Francis3PSY 310: Sensory and Perceptual ProcessesPurdue UniversityApparent Motion When objects move, there is a continuous path ofmotion But, continuous paths are not necessary for motion to beseen Motion in movies, TV, computers is all apparentmotionTime1Time2Purdue UniversityKorte’s laws Apparent motion was highly studied at the turn ofthe 20th century Korte (1915) noted that to get good motion, you neededto increase the ISI between the stimuli as the distancebetween them increased ISI just rightProf. Greg Francis4PSY 310: Sensory and Perceptual ProcessesPurdue UniversityKorte’s laws Apparent motion was highly studied at the turn of the 20thcentury Korte (1915) noted that to get good motion, you needed toincrease the ISI between the stimuli as the distance betweenthem increased ISI too brief (simultaneity)Purdue UniversityKorte’s laws Apparent motion was highly studied at the turn of the 20thcentury Korte (1915) noted that to get good motion, you needed toincrease the ISI between the stimuli as the distance betweenthem increased ISI too long (separate dots)Prof. Greg Francis5PSY 310: Sensory and Perceptual ProcessesPurdue UniversityKorte’s laws Compare to CogLab data (68 subjects)Purdue UniversityInduced movement A non-moving object can appear to be moving ifobjects around it are moving Sometimes with the flow of motion Example from textbook Sometimes the opposite direction Nearby car or train moves, but it feels like you havemoved Moon-in-the-clouds illusion Hard to demo because they work best in isolatedconditions Motion dominates the field of view, while the induced object isisolated within the fieldProf. Greg Francis6PSY 310: Sensory and Perceptual ProcessesPurdue UniversityMovement aftereffect competition betweenopposite directions ofmotion Left-right Up-down habituating gate offset of one direction leads torebound in other Motion aftereffectPurdue UniversityDetecting motion Just like depth, brightness, color, and many other aspects ofperception We do not have direct awareness of motion Instead, the visual system computes motion based onpatterns on the retina Both space and time And using information about movement of our bodies / eyes Your textbook gives a description of a simple circuit todetection motion It is not a good model of motion detection Although it could be elaborated to work properlyProf. Greg Francis7PSY 310: Sensory and Perceptual ProcessesPurdue UniversityTextbook model It’s instructive to discuss the problem with the textbookmodel because it highlights some aspects of motionperception Here’s a little diagram of the modelinhibitionexcitationexcitationmotion signalPurdue UniversityTextbook model Suppose a dot moves from left to rightinhibitionexcitationexcitationmotion signalProf. Greg Francis8PSY 310: Sensory and Perceptual ProcessesPurdue UniversityTextbook model When the dot is here it activates these cellsinhibitionexcitationexcitationmotion signalPurdue UniversityTextbook model Which inhibits the other cell Meanwhile the dot is movinginhibitionexcitationexcitationmotion signalProf. Greg Francis9PSY 310: Sensory and Perceptual ProcessesPurdue UniversityTextbook model When the dot hits here, the cell may still be inhibited, even thoughthe receptor is excited No motion detectedinhibitionexcitationexcitationmotion signalPurdue UniversityTextbook model Suppose a dot moves from right to leftinhibitionexcitationexcitationmotion signalProf. Greg Francis10PSY 310: Sensory and Perceptual ProcessesPurdue UniversityTextbook model When the dot is here it activates these cellsinhibitionexcitationexcitationmotion signalPurdue UniversityTextbook model The signal continues even while the dot movesinhibitionexcitationexcitationmotion signalProf. Greg Francis11PSY 310: Sensory and Perceptual ProcessesPurdue UniversityTextbook model When the dot reaches the other receptor, that receptor respondsinhibitionexcitationexcitationmotion signalPurdue UniversityTextbook model When the dot reaches the other receptor, that receptor responds And inhibits the other cell, but it is too late to stop the motion signalinhibitionexcitationexcitationmotion signalProf. Greg Francis12PSY 310: Sensory and Perceptual ProcessesPurdue UniversityTextbook model What’s the problem? A motion detector should not respond to a stationary dot But this circuit doesinhibitionexcitationexcitationmotion signalPurdue UniversityReichardt detector A better model looks similar, but has different calculations Here the signals from the two receptors multiply The signal on the left is delayed relative to the one on the rightdelayexcitationexcitationmotion signalProf. Greg Francis13PSY 310: Sensory and Perceptual ProcessesPurdue UniversityReichardt detector Suppose a dot moves from right to left Here it activates the receptor There is no motion signal because the x-cell needs input from bothsourcesdelayexcitationexcitationmotion signalPurdue UniversityReichardt detector The dot


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Purdue PSY 31000 - Motion perception

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