The role of inhibition in the regulation of sequential action

We investigated the regulation of sequential action using a new paradigm. Participants learned a sequence of seven stimulus categories and then monitored for them during successive displays. All displays were instances of these categories, presented in pseudo-random order. On each trial, participants monitored for an instance of Category 1, pressed a key on a computer keyboard, then monitored for an instance of Category 2, pressed a key on the keyboard and so on for all seven categories. Thcrs, a perfect trial contained exactly seven responses. Intrusion errors were classified as a function of ordinal distance front the cur-rent serial position (n). Fewer intrusion errors were made at near serial positions than at far ones, suggesting a gradient of lateral inhibition. In addition, more intrusions were made on n + I categories than n - I categories, suggesting greater availability of intended than completed goals. In accord with current models of sequential action, the results indicate lateral and self-inhibition as important mechanisms in regulation of sequential action.