The spatial distribution of attention in S-R compatibility

In certain choice reaction time experiments the subjects, although not specifically instructed to do so, perform a parcellation of space into right and left components. Previous research has shown that when the stimulus locations are marked on the screen, the subdivision of space into right and left halves is bound to the point where the subject has been instructed to focus selective attention. It is not known whether, in the absence of specific instructions, subjects are able to focus selective attention between stimulus locations when no marker is present. We tried to clarify this problem by introducing a 'probe' stimulus that could map the spatial distribution of attention in subjects engaged in a compatibility task. The results suggest that, in the absence of visual cues marking the stimulus positions, attention is kept in the disengaged modality before the presentation of the stimuli. In this state of disengagement a powerful tendency to orient to the rightmost side of the display, within each visual field, is apparent. Various interpretations of this finding are discussed.