Practice-induced and sequential modulations of the Simon effect

People react faster and more accurately to stimuli presented in locations corresponding to the response, compared to noncorresponding locations, even when stimulus location is irrelevant (SE = Simon effect). The explanation that SEs are caused by the automatic priming of a corresponding response has been questioned, because of the many exceptions to the effect. We replicated practice-induced and sequential modulations of the SE in two experiments, first by training participants with blocks of location relevant stimuli, and second by mixing location relevant and irrelevant trials. The decrease of the SE with incompatible training is relatively permanent in the blocked experiment, whereas the effect is temporary in the mixed experiment. The difference is caused by a more permanent reversal of the SE after incongruent trials, showing that sequential modulations depend on long-term practice effects. We suggest the formation of a contralateral long-term memory stimulus-response link in blocked conditions, and that short-term and long-term memory links are primed by preceding events.