On the modularity of sequence representation

A modular theory of motor control posits that the representation of an action sequence is independent of the effector (motor) system that implements the sequence. Three experiments tested this theory. Each used a variant of a method developed by Nissen and Bullemer (1987) in which subjects responded to visual signals occupying different spatial positions by pressing a key corresponding to each signal position. Sequence learning is indicated when reaction times to signals that follow a sequence become faster with practice than reaction times to random signals. The first experiment showed transfer of sequential learning of key pressing from the fingers to the arms, or vice versa. Similar transfer was found when a distraction task was added that likely blocked an attentional form of learning (cf. Curran and Keele, 1993). In a third experiment, much but not all of the sequential learning transferred from a situation in which the response was a key press to one with a vocal response, suggesting that at least part of the sequential learning is embedded in a system that describes successive locations of signals in space. These studies suggest that sequential representation resides in a module prior to the selection of effector systems to execute the movement.