The accessory Simon effect within and across visual dimensions.

The Dimension-Action model maintains that response selection in the visual system is modular, such that response selection based on a target's feature occurs within modules. This study suggests that response selection processes based on a target's spatial location occur within modules as well, where spatial locations are coded along with the feature information. From this perspective, the typical Simon effect, in which interference occurs between a target's feature and its spatial location, occurs within modules. This study explored whether the unique characteristic of the spatial Simon, namely, its reduction with increased reaction time is typical of spatial intra-dimension but not of spatial cross-dimension Simon effects, using the accessory Simon task. Experiment 1 demonstrated that intra-dimension Simon effects were reduced with increased reaction time, a reduction that was modulated by the task relevance of the distractor. In contrast, cross-dimension accessory Simon effects were positive and increased with reaction time. Experiment 2 demonstrated that intra-dimension Simon effects were not reduced when space was conveyed symbolically by arrows. Overall, the study suggests that interference in the accessory Simon task is influenced not only by the nature of the irrelevant spatial information but also by the modular locus of the targets and distractors.