On the time-course of automatic response activation in the Simon task

The Simon effect (prolonged RT when the task-irrelevant stimulus location is incongruent with the response side) has been reported to decrease at longer RTs, which is reflected in negative-going delta functions. This finding has been attributed to gradual dissipation of the response automatically activated by the task-irrelevant location information. The Diffusion Model for Conflict Tasks (DMC, Ulrich, Schroter, Leuthold, & Birngruber, Cognitive Psychology 78:148-174, 2015) formally specifies the time-course of this automatic activation process as a pulse-like function. In contrast to alternative views, DMC is consistent with the notion that this time-course is unaffected by the presentation duration of the target stimulus. Therefore, we expected that delta functions are invariant against changes of stimulus duration. This prediction was verified in two Simon task experiments. Consistent with this general result, DMC's parameter tau which defines the time-course of the automatic response activation was estimated to not meaningfully differ between short and long durations. We argue that our results are coherent with processing architectures that assume a transient automatic process that is virtually unaffected by stimulus duration.