Effects of inter- and intramodal selective attention to non-spatial visualstimuli: an event-related potential analysis

Event-related potentials (ERPs) were recorded to trains of rapidly presente d auditory and visual stimuli. ERPs in conditions in which subjects attende d to different features of Visual stimuli were compared with ERPs to the sa me type of stimuli when subjects attended to different features of auditory stimuli. This design permitted us to study effects of variations in both i ntramodal and intermodal visual attention on the timing and topography of E RP components in the same experiment. There were no indications that exogen ous N110, P140 and N180 components to line gratings of high and low spatial frequencies were modulated by either intra- or intermodal forms of attenti on. Furthermore, intramodal and intermodal attention effects on ERPs showed similar topographical distributions. These combined findings suggest that the same neural generators in extrastriate occipital areas are involved in both forms of attention. Visual ERPs elicited in the condition in which sub jects were engaged in auditory selective attention showed a large positive displacement at the occipital scalp sites relative to ERPs to attended and unattended stimuli in the visual condition. The early onset of this positiv ity might be associated with a highly confident and early rejection of the irrelevant visual stimuli, when these stimuli are presented among auditory stimuli. In addition, the later onset of selection potentials in the intram odal condition suggests that a more precise stimulus selection is needed wh en features of visual stimuli are rejected among other features of the same stimulus pattern, than when visual stimuli are rejected among stimuli of a nother modality. (C) 1998 Published by Elsevier Science B.V. All rights res erved.