What visual image information is needed for the things we do?

1. What visual image information is needed for the things we do? How is vision used to acquire information from the world?

2. Types of Eye Movement Information GatheringStabilizing Voluntary (attention) Reflexive Saccades vestibular ocular reflex (vor) new location, high velocity, ballistic body movements Smooth pursuit optokinetic nystagmus (okn) object moves, velocity, slow whole field image motion Vergence change point of fixation in depth slow, disjunctive (eyes rotate in opposite directions) (all others are conjunctive) Fixation: period when eye is relatively stationary between saccades.

4. X smooth pursuit saccade X Catching: Gaze Patterns X Thrower Catcher Terminology: saccadic eye movement

5. Saccade reaction time = 200ms Catching: GazeAnticipation 61 ms X X -53 ms X Thrower Catcher Timing of departure and arrival linked to critical events

7. What is the significance of prediction?Brain must learn the way ball moves etc and programmovement for an expected state of world. Not reacting simply to current visual information. Stimulus Response What is meant by an “internal model”?

8. Why is prediction necessary? Analysis of visual signals takes a lot of time! Photoreceptors ganglion cells LGN Primary visual cortex other cortical areas mid-brain brain stem muscles Round trip from eye to brain to muscles takes a minumum of 200 msec. Cricket ball only takes about 600 msec. Prediction gets around the problem of sensory delays.

9. How good is Internal Model? Accuracy of Fixations near Bounce 20 deg bouncepoint 2D elevation Subjects fixate above the bounce point

10. Poor tracking when ball is unexpectedly bouncy

11. Better tracking 2 trials later.

12. Pursuit accuracy following bounce Measure proportion of time between bounce & catch that eye is close to ball tennis ball bouncy ball 5 subjects Does pursuit accuracy improve with repeated trials? Does it matter which ball is used first? What can we conclude if it does?

13. Prediction in Squash

14. Prediction in Squash

16. “Reduced gain” means eye lags behind ball. “Gain” = 1 means perfect tracking These speeds are much higher than expected. Too high for a reactive system. That is, prediction is necessary.100deg/sec = 10 deg in 100 msec.

17. Macular degeneration patient (blind in central 15 deg field) Fovea not necessary for smooth pursuit - can learn to use other regions

18. Binocular Vision Stereoscopic information: image in the two eyes is different. This information is used to perceive the depth relations in the scene. • When is stereoscopic information useful? • - reaching and grasping • walking over obstacles • catching?? Development of stereoscopic vision - amblyopia/ astigmatism - critical period

19. Difference in retinal distance between the objects in the two eyes is called “retinal disparity” and is used to calculate relative depth.

20. Binocular Vision

21. Monocular Vision

22. Other information that may be useful for catching. Motion parallax: change in relative position of objects at different depths when the head moves. Looming: image of ball increases in size as ball gets closer. Rate of change of size can be used to calculate “time-to-contact” Pursuit movement: keeping the eye on the ball.

23. target selection Planning? saccade decision saccade command inhibits SC Cerebellum Learning? signals to muscles

24. decision to pursue/attention detect/analyze retinal image motion Supplementary eye fields planning? prediction/ learning? signals to muscles

25. Even the simplest action must involve linkage between memory, vision, eye movements, and body movements. from Land et al, 1999

26. 1.What are the questions? • Is the behavior observed by Land in cricket also true for a simple task like catching a ball? • What eye movements are made in this case? • Do subjects anticipate the bounce point? By how much? • Do Subjects look at floor or above the bounce point? • What happens after bounce? • How do subjects adjust to different balls? • ….. • Is there a difference between throwing and catching? Why? • What eye movements are made when observing others throw and catch? • Similarity between individuals? • When do the hands start to move? • 2. Choice of task: • Catching and throwing a ball. • 3. Procedure: • Select subject and calibrate eye tracker. Three people stand at equal distances apart and throw the ball back and forth, with a bounce in the trajectory. Need to measure this distance. • First throw in a predictable manner, about 8 times. • Then use a different ball, 8 trials. • Other balls… • Compare one versus two eyes???

27. 2. Data analysis • Label your tape. Play it frame-by-frame on the VCR in the lab. • …. • What to look for: • Describe eye movements sequence for each trial • eg Trial 1: fixate near hands/saccade to bounce point/fixate/track portion of trajectory/fixate for last part of trajectory (??) • Trial 2: fixate near hands/saccade to bounce point/fixate/track portion of trajectory/fixate for last part of trajectory (??) • …. • B How regular is the sequence of movements? • C What is the timing of the saccades/fixations/tracking relative to movement of the ball. How much do subjects anticipate the bounce point, if at all? • D. How accurate are fixations near the bounce point? (Need to measure visual angle.) • Compare different conditions. • What happens with the different balls? Do the eye movements change with additional experience? How quickly do they adjust? • Other Aspects: • How similar are different individuals? Where would we expect similarities/ differences? • What is the role of the pursuit movement? If pursuit is made only on final bounce, implies pursuit is used to guide hands. Maybe position of eye in head. • Binocular information versus monocular (looming)

28. Different gaze pattern for watching but still anticipate bounce and catch events.

29. saccade X X Gaze Patterns Different when Watching X Thrower Catcher

30. Watching:Gaze Anticipation -517 ms -51 ms X X -167 ms X Thrower Catcher Head rotation begins 200-500 msec before release