Response Preparation and the Simon Effect: Experimental and Model-Based Analyses.

In choice between frequent and infrequent responses the Simon effect is larger for the frequent than for the infrequent response. We arbitrate between three hypotheses to account for this finding. The first hypothesis holds that it is a straightforward consequence of biased response preparation. The second hypothesis posits a facilitation of the shift of visual attention to the side of the prepared response in addition, and the third one an effect of the different frequencies of congruent and incongruent trials associated with the task-irrelevant stimulus locations. In three experiments we show the modulation of the Simon effect by relative response frequency, its independence from the distance between hands and monitor, and its almost complete elimination by valid response cues. These findings are in line with a primary role of biased response preparation. Consistent with this conclusion, in a model-based analysis, using extensions of the Leaky, Competing Accumulator model, differences between the probabilities of preparing the frequent and infrequent response were sufficient to produce the modulation of the Simon effect, though only poorly its dynamics as assessed by delta plots. However, these dynamics were produced by a model which implemented the hypothesis that response preparation implicates shielding against distraction in addition to anticipatory response activation. According to simulation results, the modulation of congruency effects by relative response frequency might depend on the particular type of congruency effect, specifically the temporal offset between the impacts of relevant and irrelevant stimuli.