Spatial compatibility between stimulated eye and response location.

It is assumed that the eye-of-origin information is restricted to the visual cortex. However, reactions to monocular stimuli are faster when the response location and the stimulated eye are ipsilateral (compatible trials) than when they are contralateral (incompatible trials). We investigated whether this spatial compatibility effect had the characteristics of the conventional visual Simon effect. We found that the size of the compatibility effect was constant throughout the reaction time distribution, and there were no electrophysiological signs of incorrect response activation. These results indicate that the spatial code derived from eye-of-origin information does not produce a transient activation of the spatially compatible response, but a more tonic influence on response selection. The results also show that monocular information can exert influence outside the visual cortex and that spatial codes can be produced in the absence of attention movements.