[Spatial stimulus-response compatibility: presentation of stimuli within one visual hemifield].

Choice reaction times of two lateralized unstructured visual stimuli located within the same (right or left) visual hemifield were studied in subjects with hands crossed and uncrossed. The subjects were instructed to respond with their right or left hand depending on the position of the stimulus. In one experimental condition they have to use their right hand for responding to the right light and their left hand for responding to the left light. In another experimental condition the reverse arrangement was used. The two light stimuli were presented, one at a time and 3 degrees apart, in both visual fields. Thus, the analyzed factors were: hand position (crossed or uncrossed), responding hand (right or left), field of presentation (right or left), and relative position of the light stimulus (right or left). The main finding of the present study was that spatial compatibility effects were present even when both stimuli were presented within the same visual field. That means that the factor determining which hand is faster in responding is the relative position of the two stimuli and of the two hands and not the position of the stimuli with reference to the vertical meridian.