2. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison1 Perception of Motion and Movement

3. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison2 Quiz: List five ways to make a spot of light appear to move: 1. Move the light 2. Apparent Motion Turn off the light, turn on another 3. Induced Motion Move a large framing object 4. Auto kinetic effect View a dim light in a very dark room 5. Movement aftereffect Move something for a long time - then look at the light 6.(Change the intensity of the light)

4. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison3 Say at V1 the neurons detected this pattern Positions across retina Orientation

5. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison4 and a moment later the neurons detected this pattern Positions across retina Orientation

6. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison5 What could be the source of this motion? Positions across retina Orientation Positions across retina Orientation

7. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison6 Sources of movement for the eye- brain system motion across the retina –object moving or eye or head or body moving? eye movement –tracking an object or just looking around? head movement body movement

8. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison7 World in motion: Eyes in motion: Categorize into four possibilities NoYes No Static Vision Retinal Motion Yes Eye/Body movement Tracking Gregory: Inflow/Outflow

9. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison8 Retinal (image) motion movement of light across retina sensitivity found in all animals –not all animals see static images –all animals see motion motion detected by some animals in retina –house fly, frog motion detected by some animals in brain –cats, humans

10. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison9 Uses of motion information 1.Relative velocity of observer and environment direction of heading, time to contact 2.Segmentation of figure from ground disruption of camouflage techniques 3.Recovery of 3D parameters motion parallax (3D depth) kinetic depth (3D shape) 4.Object identification humans, friend/foe

11. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison10 Centre of expansion ------> = direction of heading 1.Relative velocity of observer and environment speed and direction of objects/observer optic flow - pattern of motion in image when observer moves

12. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison11 Optic flow demo Optic flow used to determine –direction of heading –time to collision –approach/avoidance types of optic flow caused by global motion –expansion/contraction (collision?) –translation –rotation Gibsonian approach uses optic flow a lot

13. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison12 2.Segmenting figure from ground Figure: object that draws our attention Ground: non-moving dots/contours/blobs Gestalt law of Common Fate –items that move together belong together From http://www.human.pefri.hr/~bsremec/figure_motion.html Common fate demo

14. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison13 3.Recovering three-dimensional shape Retinas can only record 2D projection of world depth dimension is lost Use motion to recover some 3D information different information from different views combine into a single 3D model (hypothesis) Two methods: a.motion parallax b.kinetic depth

15. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison14 a. Motion parallax: different viewpoints recover depth

16. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison15 a. Motion parallax: different viewpoints recover depth

17. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison16 b. Kinetic depth different views recover shape

18. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison17 4.Object identification motion pattern identifies object visual form masked by “stuff”, such as trees, leaves smoke bad vision distance low lighting

19. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison18 From http://www-white.media.mit.edu/~jdavis/ MotionTemplates/motiontemplates.html Davis

20. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison19 From my research! PLD

21. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison20 Point light displays (Johansson) separate visual form and motion pattern robust detection even with distractors –separation of figure and ground accurate determination –sex, friends, animals, emotional affect, action humans only really good at recognizing humans –relies on human motor control system –“if I could move like that then it could be like me” but humans are pretty good at recognizing everything

22. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison21 Finally What was the purpose of this presentation? Which question remains unanswered?

23. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison22 Detecting image motion It moved!

24. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison23 Motion detection versus perception detection: low level process –low level, like edge detection perception: higher level process –high level, like object identification how do we know that we have specific neurons for motion detection? how do we know that we have specific centers for motion perception?

25. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison24 Specific neurons for motion detection motion after effect –similar to colour after effect (“negative” after starring at image)

26. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison25 Bang! The Canadian Flag!

27. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison26 Motion aftereffect shape not affected adaptation to motion independent of shape separate systems for motion and shape! (and colour!)

28. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison27 Neurons specialized for motion detection 1960-1970s –frogs (“bug”, “predator” detectors) –house fly (optic flow) –rabbit –cat (string, yarn -- just kidding) –monkey model proposed: Reichardt detector

29. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison28 Motion detected Reichardt detector correlator + two different inputs –one input has a delay

30. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison29 Directionally sensitive fires for change in one direction, not in other

31. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison30 Temporally sensitive fires for change over particular interval change too fast: first spike arrives too late change too slow: first spike arrive too early

32. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison31 Take home message only a particular speed and direction sets off any particular Reichardt detector

33. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison32 Apparent Motion (NOT phi motion) 1.A visible item suddenly disappears 2.A new item appears soon afterwards at neighboring location Perception: the original item “moves” to a new location Where have you seen this?

34. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison33 Apparent Motion (NOT phi motion) 1.A visible item suddenly disappears 2.A new item appears soon afterwards at neighboring location Perception: the original item “moves” to a new location Where have you seen this?

35. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison34 Apparent motion constraints 1.not influenced by cognition - pops out 2.short spatial range (< 0.25°) 3.short temporal range (< 80ms) 4.many objects at once 5.very much like “real” motion detection

36. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison35 Motion detected Motion detected Explanation of apparent motion Reichardt detector –can detect continuous motion

37. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison36 Explanation of apparent motion Reichardt detector –can detect sudden “jumps” –cannot distinguish them

38. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison37 Applications of apparent motion Movies and Television –Reichardt detectors cannot distinguish “real” from “artificial” motion Present a sequence of frames/static images –seen the same as real motion Requires proper timing –separation between frames < 80ms Movies: 24 FPS = 1/24 seconds = 41ms TV: 30 FPS = 1/30 = 33ms

39. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison38 Importance of context Reichardt detectors do not completely account for motion perception Just as lateral inhibition does not completely account for brightness perception Context counts! –Apparent motion of the human body –Perception of motion can occur (or be misperceived) -> induced motion

40. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison39 Apparent motion of the human body Shiffrar and Freyd (1990) 1.image of human in one pose 2.delay 3.image of human in second pose 4.chose from one of four motion paths results: physically plausible paths require delays approximately equal to real world motion

41. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison40 Shiffrar and Freyd: Implications brain takes into account typical movement patterns brain “knows” how long a movement should take brain uses motor control and perception centers to form perceived motion path

42. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison41 Downing et al (2001) EBA: extrastriate body area active when viewing human bodies

43. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison42

44. Induced motion demo

45. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison44 Induced motion when two items are present, smaller one is seen to move slightly, even if it isn’t moving Explanation –motion is relative –larger object more likely to be not moving

46. Gregory Induced Motion Demo

47. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison46 Is object/world moving or eye?? see Gregory pp 99-105

48. 1/29/2002PSYC202-005, Term 2, Copyright 2002 Jason Harrison47 Finally What was the purpose of this presentation? Which question remains unanswered?