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Motion Perception

Motion Perception. PSY 295 – Sensation & Perception Christopher DiMattina , PhD. Motion. Motion. Motion is change in an object’s position over time. Waterfall illusion. A circuit for detecting motion. Why might this not be a good motion-detector?.

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Motion Perception

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  1. Motion Perception PSY 295 – Sensation & Perception Christopher DiMattina, PhD

  2. Motion PSY 295 - Grinnell College - Fall 2012

  3. Motion • Motion is change in an object’s position over time PSY 295 - Grinnell College - Fall 2012

  4. Waterfall illusion PSY 295 - Grinnell College - Fall 2012

  5. A circuit for detecting motion • Why might this not be a good motion-detector? PSY 295 - Grinnell College - Fall 2012

  6. Cannot tell a large bug from small moving bug PSY 295 - Grinnell College - Fall 2012

  7. A better circuit • Include a rapidly adapting delayed inter-neuron and multiplicative neuron which must get simultaneous inputs PSY 295 - Grinnell College - Fall 2012

  8. Can extend to many stages PSY 295 - Grinnell College - Fall 2012

  9. Properties of our motion detector • Direction sensitive • Velocity tuned • Not responsive to large stationary objects PSY 295 - Grinnell College - Fall 2012

  10. A feature, not a bug • Object does not actually need to move: Can disappear and then re-appear to the right at the appropriate time delay PSY 295 - Grinnell College - Fall 2012

  11. Apparent motion • We experience apparent motion whenever we watch television, movies and cartoons PSY 295 - Grinnell College - Fall 2012

  12. Flip-books • http://www.youtube.com/watch?v=DfaSIHjnxPQ&feature=related PSY 295 - Grinnell College - Fall 2012

  13. Web activity • http://sites.sinauer.com/wolfe3e/chap8/mottypesF.htm PSY 295 - Grinnell College - Fall 2012

  14. The correspondence problem • Which feature in frame 2 corresponds to feature in frame 1? PSY 295 - Grinnell College - Fall 2012

  15. The aperture problem • Each V1 neuron only sees a small window of world • Local signal is consistent with multiple global motions PSY 295 - Grinnell College - Fall 2012

  16. The aperture problem PSY 295 - Grinnell College - Fall 2012

  17. Web activity • http://sites.sinauer.com/wolfe3e/chap8/mottypesF.htm PSY 295 - Grinnell College - Fall 2012

  18. Neural Coding of Motion PSY 295 - Grinnell College - Fall 2012

  19. Visual pathways • Magnocellular neurons in LGN sensitive to motion • Information goes to area V1 and then to an area specialized for motion processing called MT (middle temporal) PSY 295 - Grinnell College - Fall 2012

  20. Direction selectivity in V1 • Hubel and Wiesel (1962) find direction selectivity in V1 PSY 295 - Grinnell College - Fall 2012

  21. Global motion detector • MT neurons insensitive to form but sensitive to global motion • Integrate information from locally direction tuned V1 cells PSY 295 - Grinnell College - Fall 2012

  22. MT and motion perception • Newsome and colleagues trained monkeys to detect arrays of coherently moving dots • Lesions of MT impair motion detection performance while leaving unaffected the ability to discriminate orientation PSY 295 - Grinnell College - Fall 2012

  23. MT and motion perception • Stimulating a column of MT neurons with a given preferred direction actually biases the monkey’s perceptions towards that direction PSY 295 - Grinnell College - Fall 2012

  24. MT and motion perception • http://cerco.ups-tlse.fr/~hupe/plaid_demo/demo_plaids.html • Cells in MT tuned to coherent pattern motion • Cells in V1 tuned to component motion PSY 295 - Grinnell College - Fall 2012

  25. Motion aftereffects • http://sites.sinauer.com/wolfe3e/chap8/maeF.htm PSY 295 - Grinnell College - Fall 2012

  26. Second-order motion • Can get motion percept in the absence of a clear figure • Random dots simply change their polarity PSY 295 - Grinnell College - Fall 2012

  27. Second-order motion demo • http://sites.sinauer.com/wolfe3e/chap8/mottypesF.htm PSY 295 - Grinnell College - Fall 2012

  28. Using Motion Information PSY 295 - Grinnell College - Fall 2012

  29. Optic flow tells us about our motion • Expansion around point of focus • http://sites.sinauer.com/wolfe3e/chap8/mottypesF.htm PSY 295 - Grinnell College - Fall 2012

  30. Biological motion • Can recognize actions using only motion cues • http://sites.sinauer.com/wolfe3e/chap8/mottypesF.htm PSY 295 - Grinnell College - Fall 2012

  31. 3-D Structure from motion • http://www.youtube.com/watch?v=RdwU28bghbQ&feature=related PSY 295 - Grinnell College - Fall 2012

  32. Demo in book • Fixate dot and move pencil across field • Next follow pencil (smooth pursuit) • Dot makes in (b) same trip across retina as pencil in (a). Why do we not perceive motion? PSY 295 - Grinnell College - Fall 2012

  33. Eye movements • We make a wide variety of eye movements and many brain regions are dedicated to moving the eyes • Vergence - focus in depth • Saccades - ballistic eye movements for fixation • Smooth pursuit - tracking moving objects PSY 295 - Grinnell College - Fall 2012

  34. Eyes move in their orbits PSY 295 - Grinnell College - Fall 2012

  35. Many brain regions dedicated to eye movements PSY 295 - Grinnell College - Fall 2012

  36. Saccades • Fixations on interesting parts of image • You cannot see your own saccades – try in mirror! • Saccadic suppression prevents world from smearing when you move your eyes PSY 295 - Grinnell College - Fall 2012

  37. Why the dot does not move PSY 295 - Grinnell College - Fall 2012

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