Abstract
Simple left-right button-push responses tend to be faster and more accurate when responses and stimuli are on the same side compared to opposite sides, even when the response is determined by a non-spatial attribute of the stimulus (e.g., color). Previous work revealed that this effect—the Simon Effect—reflects interference within response selection processes, and that the spatial reference frame is defined at least in part by the focus of attention. The Simon Effect, therefore, constitutes a simple domain within which to study interactions between perception, attention, and action. A limitation, however, is that the Simon Effect has been studied almost exclusively using two-dimensional displays (i.e. computer monitors), whereas we attend and act within a three-dimensional world. We measured the Simon Effect for multiple left-right stimulus separations with stimuli at near (reachable) or far (unreachable) distances within a virtual reality environment. Stimuli were colored poles that afforded grabbing. Left-right responses were based on the color of the pole, and congruence was defined by the match between the response hand and the side of the world in which pole appeared. For one group, left-right separations were matched across reachable and unreachable space in terms of distance in the world, rather than distance in the image. For a second group, separations were matched in terms of distance in the image, rather than distance in the world. Results revealed robust Simon Effects in both reachable and unreachable space, but they were larger in reachable space than unreachable space, regardless of how separation was controlled. This work indicates that stimulus-response congruence effects can depend on the perceived reachability of stimuli, and provides a foundation for exploring perceptual-motor interactions within a realistic but controllable context.