ABSTRACTS

Effects of inter- and intramodal selective attention to nonspatial visual stimuli: topographical and chronometrical analyses.

Albert Kok, Michiel de Ruiter and Menno van der Schoot# Psychonomics Department, University of Amsterdam, #Department of Child Psychology,

Free University. Amsterdam, The Netherlands.

In the present study event-related potentials (ERPs) to visual stimuli in conditions in which subjects attended to visual stimuli among other visual stimuli (line gratings), were compared with the ERPs to the same visual stimuli when subjects attended to auditory stimuli among other auditory stimuli (tone pips). The main question we hoped to answer with this study was to what extent inter- and intramodal forms of visual attention involved the same or different mechanisms. There were no indications that intermodal or intramodal forms of

attention modulated exogenous NII0/PI40 and NI80 to line gratings of low and high spatial frequencies, respectively. Furthermore, scalp current-source density distributions of the intermodal visual attention effects on ERPs resembled the distributions of effects associated with intramodal visual attention. Like intramodal selective attention, effects of intermodal attention involved occipital selection negativity and frontal selection positivity around 200-300 ms. However, intramodal visual attention produced a later onset of these selection potentials than intermodal attention. This probably indicates that a more precise stimulus selection is needed when visual stimuli are selected among other visual stimuli, than when the same stimuli are selected (or: rejected) among stimuli of another modality. Visual ERPs elicited in the auditory attention condition showed a

large positive displacement at Oz in comparison with ERPs to attended and unattended visual stimuli in the visual attention condition. The relative early onset of this positivity might be associated with a highly confident and abrupt rejection of the irrelevant visual stimuli, when these stimuli are presented among auditory stimuli.

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