Effects of cross-modal selective attention on early negative difference of event-related potentials

Methods. Event-related potentials (ERPs) were measured in 12 healthy subjects aged 19-22 years using the reformed oddball paradigm "cross-modal and delayed-response". In experiment 1, subjects attended visual modality and ignored auditory modality. In experiment 2, subjects attended auditory modality and ignored visual modality. The difference wave was obtained by subtracting ERPs in unattended condition from those in attended condition. Results. 1. There was an enhancement of the N1 elicited by standard stimuli in auditory and visual modalities and by deviant stimuli in the visual modality under attended condition. 2. The onset time and scalp distribution of both attentive N1 and Nd1 were similar regardless of standard or deviant stimuli in the auditory and visual modality; the onset time of Nd1 elicited by auditory and Visual deviant stimuli was earlier than that of the unattended N1, and their scalp distributions were different. 3. The Nd1 components elicited by auditory and visual deviant stimuli were distributed, respectively, over the primary sensory areas, but Nd1 components evoked by auditory and Visual standard stimuli were distributed over the frontal scalp. Conclusions. These results suggest that the attended N1 enhancement is, at least mainly, caused by a component with endogenous origins; that the early attention effect occurs before the exogenous components; and that the processing location of cross-modal attention to deviant stimuli is modality specificity and to standard stimuli is supramodal mechanism.