Hemispheric Asymmetry of Exogenous Orienting of Attention: Inferences from Reaction Time, P1 and N1 Amplitude

The effect of exogenous orienting of attention on reaction time (RT) critically depends on the stimulus onset asynchrony (SOA) between cue and target: RT is shorter for cued target locations (facilitation) when the SOA is short, whereas this RT effect reverses when the SOA is long (inhibition). In the present study we were primarily interested in the lateralization of exogenous visuospatial attention mechanisms, as these are known to depend in right-handers predominantly on the right hemisphere. Specifically, we recorded event related brain potentials (ERPs) to investigate how hemispheric lateralization of attention modulates facilitation and inhibition effects. Thirty right-handed participants performed a Posner-like cueing task (p(valid) 5 .50) using SOAs of 200 and 800 ms, in which go-nogo responses were demanded to the visual target stimulus. RTs showed an asymmetric facilitation effect that was larger for right visual field targets. Visual ERP components over lateral occipito-temporal sites (P1,N1) indicated that facilitation and inhibition influenced already early stages of visual processing. Crucially, for the short SOA, it was only for targets displayed in the left visual field that the contralateral P1 was enhanced for valid trials. Moreover, no hemispheric asymmetries, neither in RT nor in P1 andN1 amplitudes, were observed with the long SOA. In conclusion, present findings support the assumption that the right hemisphere plays a dominant role in exogenous orienting of visuospatial attention