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Visual feedback in the control of reaching movements

Visual feedback in the control of reaching movements. David Knill and Jeff Saunders. Two types of motor control. Ballistic Feedback control. Ballistic control. Motor commands. Target state. Motor planning. Physical plant. New System states. Initial system state.

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Visual feedback in the control of reaching movements

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  1. Visual feedback in the control of reaching movements David Knill and Jeff Saunders

  2. Two types of motor control • Ballistic • Feedback control

  3. Ballistic control Motor commands Target state Motor planning Physical plant New System states Initial system state

  4. Feedback control Motor commands Target state Motor planning Physical plant New System states Initial System state Sensory system

  5. Baseball examples • Ballistic control • Hitting • Throwing • Feedback control • Running to catch a ball

  6. Target

  7. Target

  8. Target

  9. Target

  10. Target

  11. Target

  12. Target

  13. Target

  14. Target

  15. Target

  16. Target

  17. Target

  18. Target

  19. Target

  20. Target

  21. Target

  22. Target

  23. Target

  24. Target

  25. Target

  26. Target

  27. Eye-hand coordination EOG signal Finger position

  28. Movement start EOG signal Finger position

  29. Speed profile for pointing movement

  30. Ballistic control Motor commands Target state Motor planning Physical plant New System states Initial system state

  31. Questions • Does the visuo-motor system use visual information about target on-line to update motor program?

  32. Feedback control Motor commands Target state Motor planning Physical plant New System states Initial System state Sensory system

  33. Questions • Does the visuo-motor system use visual information about target on-line to update motor program? • Does the visuo-motor system use continuous feedback from the hand during a movement to control the movement

  34. Questions • Does the visuo-motor system use visual information about target on-line to update motor program? • Does the visuo-motor system use continuous feedback from the hand during a movement to control the movement • What visual information is used?

  35. Question • Does the visuo-motor system use visual information about target on-line to update motor program?

  36. Question • Does the visuo-motor system use visual information about target on-line to update motor program? • Yes - for detectable target motion (e.g. catching a moving object)

  37. Question • Does the visuo-motor system use visual information about target on-line to update motor program? • Yes - for detectable target motion (e.g. catching a moving object) • ?? - for imperceptible changes in target position

  38. Experiment • Perturb position of target during a saccade (imperceptible change) • Does motor system correct for change in target position?

  39. Perturbed trials Unperturbed trials

  40. Results • Automatically correct for imperceptible target perturbations. • Correct for perturbations • Perpendicular to movement • In direction of movement • Reaction time = 150 ms • Smooth corrections

  41. Question • Does the visuo-motor system use continuous feedback from the hand during a movement to control the movement?

  42. Hypotheses • Classic model • Ballistic control during “fast” phase of motion • Feedback control during end, “slow” phase of motion • Continuous model • Feedback control throughout movement

  43. Arguments against continuous feedback • Visuo-motor delay (~100 ms) is too large for effective control during fast phase. • Removing vision of hand early in motion does not affect end-point error. • Corrections to target perturbations are just as strong with or w/o vision of hand.

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