On the importance of being first: serial order effects in the interaction between action plans and ongoing actions.

When we plan sequences of actions, we must hold some elements of the sequence in working memory (WM) while we execute others. Research shows that execution of an action can be delayed if it partly overlaps (vs. does not overlap) with another action plan maintained in WM (partial repetition cost). However, it is not known whether all features of the action maintained in WM interfere equally with current actions. Most serial models of memory and action assume that interference will be equal, because all action features in the sequence should be activated to an equal degree in parallel; others assume that action features earlier in the sequence will interfere more than those later in the sequence, because earlier features will be more active. Using a partial repetition paradigm, this study examined whether serial position of action features in action sequences maintained in WM have an influence on current actions. Two stimulus events occurred in a sequence, and participants planned and maintained an action sequence to the first event (action A) in WM while executing a speeded response to the second event (action B). Results showed delayed execution of action B when it matched the first feature in the action A sequence (partial repetition cost), but not when it matched the last feature. These findings suggest that serial order is represented in the action plan prior to response execution, consistent with models that assume that serial order is represented by a primacy gradient of parallel feature activation prior to action execution.

What makes an event: temporal integration of stimuli or actions?

In this article, we ask what serves as the "glue" that temporarily links information to form an event in an active observer. We examined whether forming a single action event in an active observer is contingent on the temporal presentation of the stimuli (hence, on the temporal availability of the action information associated with these stimuli), or on the learned temporal execution of the actions associated with the stimuli, or on both. A partial-repetition paradigm was used to assess the boundaries of an event for which the temporal properties of the stimuli (i.e., presented either simultaneously or temporally separate) and the intended execution of the actions associated with these stimuli (i.e., executed as one, temporally integrated, response or as two temporally separate responses) were manipulated. The results showed that the temporal features of action execution determined whether one or more events were constructed; the temporal presentation of the stimuli (and hence the availability of their associated actions) did not. This suggests that the action representation, or "task goal," served as the "glue" in forming an event in an active observer. These findings emphasize the importance of action planning in event construction in an active observer.