Invariant relative timing in motor-program theory
One of the aggravations in motor research is the large number of different human movements. Although everyday language provides well-established categories to manage this manifold, there is no well-defined and generally accepted classification system that satisfies scientific criteria. In the face of an almost unlimited variability, it is comforting to have some invariant characteristics. Invariant features can be used as defining characteristics for sets of movements. More importantly, they suggest inferences about the nature of internal representations or structures that underlie movement production. This chapter is about an invariance that has received a great deal of attention, the invariance of relative timing. The chapter describes the phenomenon and its incorporation into a particular kind of theory, the notion of a generalized motor program. Several points of criticism are discussed in the chapter that can be raised against the phenomenon and its theoretical underpinnings. Finally, a relaxed concept of a generalized motor program is outlined in the chapter.