Primary Cortical Sub-divisions

The mapping of objects in space onto the visual cortex

Visual Projections

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

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

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

Smooth pursuit & Supplementary Brain Circuitry for Pursuit

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

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.

Eye movements in cricket: Batsman anticipate bounce point Better batsman arrive earlier Land & MacLeod, 2001 pursuitsaccade

Photoreceptors ganglion cells LGN Primary visual cortex other cortical areas mid-brain brain stem muscles Why are eye movements predictive? Analysis of visual signals takes a lot of time! 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.

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

Types of Eye Movement Information GatheringStabilizing Voluntary (attention)Reflexive Saccadesvestibular ocular reflex (vor) new location, high velocity, ballisticbody movements Smooth pursuitoptokinetic 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.

Figure 6.22 Vergence

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

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

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

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

Catcher Thrower saccade X X Gaze Patterns Different when Watching X

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???

2.Data analysis 2.Play video frame-by-frame using Video-Viewer software. …. 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)