The organization of rapid movement sequences as a function of sequence length

Abstract

An experiment was performed to test the predictions made by the subprogram retrieval model (Sternberg et al. 1978) for the production of rapid movement sequences, and to search for the maximum number of elements that can be planned in advance of sequence execution. Subjects performed rapid sequences of 1 to 8 finger taps under both simple and choice RT conditions. Increasing sequence length had no effect on choice RT, but caused simple RT to increase nonlinearly, with the greatest effect between 1 and 3 taps. Intertap intervals did not increase as a function of sequence length. The sequences' timing and force patterns suggested that sequences up to 8 taps were organized as single performance units. The results indicate a fundamental difference between activating a plan for a single tap and a sequence plan in which several elements must be coordinated and timed. Increasing the number of elements beyond 3 does not necessarily add processing steps in the selection and activation of the sequence plan, at least for sequences involving the repetition of a simple element.