Choosing Between Movement Sequences
David A. Rosenbaum Edward Saltzman Abigail Kingman School of Communications and Cognitive Science Hampshire College Amherst, Massachusetts
How are motor programs prepared for forthcoming movement sequences? To address this question, we have conducted choice reaction time (RT) experiments in which subjects perform one of two possible sequences of finger responses as quickly and accurately as possible. The main empirical question is how the time to produce each response in the selected sequence depends on the length of that sequence, the length of the other sequence, and the relationship between the two. We ask this question following up previous research by Sternberg, Monsell, Knoll, & Wright ( 1978) which reported systematic effects of sequence length on simple RTs. Sternberg et al. used their results to formulate an explicit model of the structure and implementation of already prepared motor programs which we use to guide our experimentation and theorizing about how motor programs are initially prepared. The model we propose says that subjects choose between two sequences of possible responses by making hierarchically based decisions: First, they choose between the two response sequences; then they choose among the responses within the response sequence that was initially selected. An important assumption in the model is that choices are only made within functional levels, never between functional levels.
Based on a wide range of behavioral and physiological studies, it is now generally accepted that voluntary movements are often controlled by detailed central