Module 2: Visual Motor Adaptation

Materials
safety goggles with prism lenses (15 diopters leftward or rightward shifts)
clay balls or bean bags (at least 15 per group)
blackboard and colored chalk (or large sheet of paper taped to wall and markers)

Description
The subject is asked to throw at a point marked by a cross on the board. Another student marks on the board where the throws land. It is important that the student always throw in the same fashion. After 10-20 throws, we can ask for a description of the throws. This introduces the concept of a baseline. How can we quantify where the throws are? An acceptable answer would be to draw a circle around the point, to indicate variance, and mark the center of that circle, to indicate an average.

The subject puts the prisms on, preferably without moving around the room, nor looking at his/her arm, and is told to "throw where you see the target". The first throws will be off target, remind them not to consciously correct their throw. It may take 30 or 50 throws, but the student will adapt to throwing on target. At that point, you can introduce the idea of sampling; the subject is not back to normal after just 1 throw.

The subject removes the goggles and continues throwing. The adaptation will remain and the throws will be off. As before, when the subject continues, the adaptation wears off and the throws are back on target.

After discussing how to properly observe what is happening, the students can be asked to give an explanation. If this module is done in conjunction with the anatomy, remind them about the cerebellum.

Other topics of discussion and experimentation:
- how long would this effect last? (over an hour)
- does the adaptation transfer to another arm or another type of throw? (no)
- where is this adaptation useful in everyday life? (if you wear glasses, looking under water, as the eyes change with age or sickness).