ABSTRACTThe effects of stimulus‐response (S‐R) spatial compatibility on reaction time (RT) and P300 component latency were studied, in order to determine whether spatial conflict effects can occur within a single cerebral hemisphere, and whether there are differences between hemispheres regarding such effects. Two choice RT experimental conditions were employed: I) an extrafoveal condition, in which stimuli (small arrows pointing either to the right or to the left) appeared laterally in one visual hemifield, the responses being given with the hand situated on the same side; likewise with the opposite hemifield and hand (cond. I); and II) a foveal condition, in which the same type of stimuli appeared centrally on the fovea, the response being given successively with both hands (cond. II). In either case, the color of the stimuli (cue information) determined which finger (forefinger or ring finger) of the same hand would deliver the response. Thus, the cue was either compatible, or not, with the stimulus orientation (arrows). In each condition, the four possible stimulus combinations, according to direction and color of the arrows, were presented at random.Results showed that: 1) in the extrafoveal condition, S‐R compatibility effects were observed in each single hemisphere, and were reflected both by RT and by P300 latency; 2) both hemispheres reacted in the same way to the spatial conflict; and 3) foveal vision increased the overall effect of the conflict on both P300 latency a