Eye movements: Lab # 1 - Catching a ball

1. Eye movements: Lab # 1 - Catching a ball

2. What can be learnt from natural tasks?

4. Gaze exclusively on task-relevant objects (see Land chapter) Eyes deal with one object at a time, corresponding to the duration of the manipulation.(Land: object-related actions) 3. Tight linkage between location of gaze and information needed at that moment. (Just-in-time strategy)

5. Why do we move our eyes? - Image stabilization - Information acquisition

6. The Eye and Retina

7. Cone Photoreceptors are densely packed in the central fovea

8. Visual Acuity matches photoreceptor density Relative visual acuity Receptor density

9. Why do we move our eyes? 1. To bring objects of interest onto high acuity region in fovea.

10. Visual Angle x a d tan(a/2) = x/d a = 2 tan-1 x/d Why eye movements are hard to measure. A small eye rotation translates into a big change in visual angle 18mm 1 diopter = 1/focal length in meters 55 diopters = 1/.018 0.3mm = 1 deg visual angle

11. 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.

12. Primary Cortical Sub-divisions

13. Visual Projections

14. Brain Circuitry for Saccades 1. Neural activity related to saccade 2. Microstimulation generates saccade 3. Lesions impair saccade V1: striate cortex Basal ganglia Oculomotor nuclei

15. Function of Different Areas monitor/plan movements target selection saccade decision saccade command inhibits SC signals to muscles

16. Posterior Parietal Cortex Intra-Parietal Sulcus: area of multi-sensory convergence reaching LIP: Lateral Intra-parietal Area Target selection for saccades: cells fire before saccade to attended object grasping

17. Brain Circuitry for Pursuit Smooth pursuit & Supplementary

18. Brain Circuitry for Pursuit Smooth pursuit & Supplementary Velocity signal Early motion analysis

19. How do we use our eyes to catch balls? What information the the brain need? Neurophysiological experiments look at single movements in response to flashes of light.

20. Batsman anticipate bounce point Better batsman arrive earlier saccade pursuit Eye movements in cricket: Land & MacLeod, 2001

21. Why are eye movements predictive? 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.

22. Is prediction seen in cricket a general property of behavior, or only seen in skilled performance like cricket or baseball?

24. X smooth pursuit saccade X Catching: Gaze Patterns X Thrower Catcher

26. Unexpected bounce leads to poor performance, particularly in the pursuit movement after the bounce. Implications of this?

28. After three trials, pursuit has improved a lot. Implications of this?

30. Different pattern of eye movements when watching (earlier, no pursuit). Implications of this?

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

32. Lab groups

33. 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? Does it correlate with performance? • Do Subjects look at floor or above the bounce point? • What happens after bounce? • How do subjects adjust to different balls? • ….. • 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, about10 times. • Then use a different ball,10 trials. • Other balls… • Compare one versus two eyes???

34. 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: • Compare timing of eye and head movements? • When do hands start to move, relative to release of ball? • 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)