The vestibular labyrinth

Hair cell responses

Neural pathways for the angular-VOR three-neuron arc

Vestibular latencyis about 15 msec

Eye movements: Lab # 1 - Catching a ball

How do we use our eyes to catch balls?What information does the brain need?

Most experiments look at simplemovements in response to targets.

What happens in the real world?

Cricket

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 minumumof 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 onlyseen in skilled performance like cricket or baseball?

Catching: Gaze Patterns

CatcherThrower

saccade X

X

smooth pursuit

X

After three trials, pursuit has improved a lot.

Implications of this?

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

Implications of this?

CatcherThrower

saccade

X

X

Gaze Patterns Different when Watching

X

Lab groups

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? • What is the difference between throwing and catching? Why?• 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. Two throw the ball back and

forth, with a bounce in the trajectory at a comfortable distance. Need to measure the distance.

• First throw in a predictable manner, about10 times.

2. Data analysis2. 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?

• 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.

Unexpected bounce leads to poor performance, particularly in thepursuit movement after the bounce.

Implications of this?