More on Motor Programs
Richard A. Schmidt University of California, Los Angeles
In studying the published research literature on motor behavior, I find it easy to come to the conclusion that motor responses are of basically two types. The notion of categorizing things into dichotomies certainly has precedent in all fields of science; in fact, Robert Benchley, the English humorist, believed that the people of the world can be neatly divided into two classes: (1) those people who believe that the world can be divided into two kinds of people; and (2) those people who do not. I want to begin this chapter with a discussion of why I think the literature indicates that motor responses can be dichotomized, and then I turn to a more complete discussion of one of those kinds of movements.
In particular, the division is along the lines of how long movements take in time. The first category contains movements that are very short in time (on the order of 200 msec or less), whereas the second category contains movements that last considerably longer than that (e.g., a few seconds). Speaking very subjectively, when we perform a movement that is very rapid, such as a kicking or striking response, we seem to plan the movement in advance and then "let it fly." We do not seem to have conscious control over the movement's execution for a short period of time, and often we find ourselves making an originally planned movement when something has happened in the environment that indicates that the movement is now clearly inappropriate (e.g., the batter who swings at a very bad pitch). On the other hand, movements that are long in time seem to have ample opportunity for conscious control; we can determine if the movement is going to