Prof. Greg Francis 5/27/081Visual Perception : MotionIIE 269: Cognitive PsychologyDr. FrancisLecture 11How movies work.Motion Motion is of tremendous importance forsurvival (Demo) Try to find the hidden bird in the figure below(http://illusionworks.com/hidden.htm)Motion We can derive a lot ofinformation about theworld from motionDetecting Motion In simple animals (like flies and frogs), we knowhow motion is detecteddelay(Reichardt detector)Detecting Motion Detects movement of a specified direction andspeed(Reichardt detector)delayDetecting Motion When something moves in the proper direction two signals meet at same time, strong response(Reichardt detector)delayProf. Greg Francis 5/27/082Detecting Motion Here’s a fancier version of the same thingDetecting Motion When something moves in the wrong direction no response(Reichardt detector)delayDetecting Motion When something goes at the wrong speed, thetiming is off e.g., too fast of movement, no response(Reichardt detector)delayDetecting Motion Change the order of the delay to get the otherdirectiondelay delayDetecting Motion Change the spacing of the detectors to getdifferent speeds  Bigger separation detects faster motiondelaydelayDetecting Motion Humans have something like Reichardt motion detectors at lots of different positions in the visual field sensitive to lots of different motion directions sensitive to lots of different motion speeds Many aspects of how we perceive motion follow from theproperties of Reichardt motion detectorsProf. Greg Francis 5/27/083Apparent Motion When objects move, there is a continuous path ofmotion Reichardt motion detectors do not requirecontinuous motion and, continuous paths are not necessary for motion to beseenTime1Time2Apparent Motion For just two stimuli, it does not depend on color shape attention cognitive priming The percept of motion does depends on stimulus duration interstimulus interval (50-200 msec) distanceKorte’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 this is what would be expected from a Reichardt detector(bigger separations involve faster movement) ISI just rightKorte’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 this is what would be expected from a Reichardt detector(bigger separations involve faster movement) ISI too brief (simultaneity)Korte’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 this is what would be expected from a Reichardt detector(bigger separations involve faster movement) ISI too long (separate dots)Korte’s laws Compare to CogLab data (137 subjects)Prof. Greg Francis 5/27/084Movies Moving pictures are convincing because ofapparent motionTime 1Time 2Movies Movie film does not run continuously throughthe projector (you would just see smear!) Instead, a shutter makes the light flash onand off for each frame (thus the noise!) Apparent motion is the basis for motion onTV, computers, and “moving” lightsAperture Problem If a bar stimulus goes beyond a cell’s receptive field,it is impossible to completely determine the directionand speed of the bar this is a property of optics that also applies to neurons with alimited receptive fieldAperture Problem Despite this limitation people tend to reportmotion in such situations in a consistent way implies that higher order systems are interpretingthe motion signals in a particular way Barber Pole illusion (http://illusionworks.com/barpole.htm)Aperture Problem Similar thingsare going onhere Breathingsquare illusionCompetition competition betweenopposite directions ofmotion Left-right Up-down habituating gate offset of one directionleads to rebound in otherProf. Greg Francis 5/27/085After effect Motion can be adopted by non-moving stimuli http://www.michaelbach.de/ot/mot_adapt/index.htmlMotion illusions Some images produce movement on their own (generally requireeye movements)Motion illusions Many other aspects of perception depend on motionConclusions Motion Perception Reichardt motion detector Apparent motion» many characteristics consistent withmotion detector Aperture Problem Lots of other issues that we haven’tdiscussedNext time Attention Magic Information processing How could you not see