The mechanism of spatial coding involved in the Simon effect remain debated, with two prominent theories - the attention-shifting account Stoffer, (Psychological Research, 53(2), 127-135, 1991) and the referential coding account Hommel, (Psychological Research, 55(3), 208-222, 1993b) - offering competing explanations why the irrelevant stimulus-location is coded. To date, neither account can fully explain all available empirical data. Most published studies rely on limited sample sizes, which constrains statistical power and leaves the field without conclusive evidence. This study directly replicated Stoffer's (Psychological Research, 53(2), 127-135, 1991) investigation into attentional subprocesses that generate the Simon effect. We manipulated target spatial position across two reference frames: a global frame based on target's screen side and a local frame defined by the relative position within each screen side, allowing us to test for both global and local Simon effects. Targets were presented inside precues, either a large box or two small boxes, which were presented simultaneously with or sequentially before the target. With an adequately-powered sample, our study revealed concurrent global and local Simon effects - a result different from Stoffer's original findings. Only the local Simon effect varied with precue type and simultaneous or sequential target presentation. These results clarify the conditions under which attentional shifting and referential coding mechanisms contribute to different Simon effects, demonstrating that when spatial target positions are defined by both global and local reference frames, these mechanisms shape the emergence of distinct Simon effects in different ways.
Baess et al. (Mon,) studied this question.