Simon says "stay in touch": Reachability moderates the effect of irrelevant spatial congruence.

The Simon Effect refers to the finding that simple left-right manual responses tend to be faster and more accurate when the response and stimulus are on the same side (congruent) compared to when they are on opposite sides (incongruent) even though the response is determined by a non-spatial attribute (e.g., color). We compared the Simon Effect with stimuli at reachable and unreachable distances within a virtual reality environment to test its dependence on the potential to interact with the stimulus. We controlled for confounds by matching image size and the viewing angle of stimuli within the environment across groups of participants. The magnitude of the Simon Effect was larger for stimuli in reachable than unreachable locations. These findings held regardless of image-size and viewing-angle conditions. This implies that task-irrelevant spatial congruence, like task-irrelevant motor affordances, is computed in ways that reflect the potential interactions with objects in a three-dimensional world.