The Schema Concept
Richard A. Schmidt University of California, Los Angeles
In the previous chapter we discussed the notion that individuals appear to move (at least in rapid movements) via the use of prestructured motor programs. We saw that the program concept is a very useful one in motor behavior because it seems to account very well for the kinds of movement effects that normally occur. But there are a few problems with the idea, some of which you have probably thought about already. In this chapter, I want to discuss some of these problems, indicating how the motor-program notion has been modified to meet these newer difficulties. Next, we turn to the question of how the performer selects the program for action, and I discuss in some detail one of the theoretical ideas that seems to explain how the performer selects appropriate movement behaviors.
A first question we might ask is, "How many programs are there?" What if I ask you to make a movement for which you already have a program--throwing a baseball, let's say--and then I ask you to change the speed of the throw. How do you do that? Do you have to have a whole new program? Implicit in the statements I have made in the previous chapter about motor programs is the idea that different responses require different programs; in order for me to have a series of pulses in memory that turn on and turn off muscles at precise times for one kind of throw, I will have to abandon the first program and generate another that does the "new " task that I want to do. How many programs do we need to throw baseballs in the infinite number of ways that we can? An infinite number, under