Electrooencephalographic activity associated with shifts of visuospatial attention

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Abstract
The neural processes underlying shifts of visuospatial attention were studied in normal adults by non-invasive recording of brain electrical activity. Event-related evoked potentials (ERPs) were recorded during target detection tasks with targets preceded by central of peripheral directional cues in the visual field, which are hypothesized to provoke voluntary and reflexive shifts of spatial attention. Reaction time to targets varied as a functionn of cue type and cue—target interval, indicating that the tasks induced shifts of spatial attention across the visual field. Event-related evoked potential recordings showed that central cues elicited negative potential shifts starting 240 ms after cue onset over posterior scalp sites contralateral to the cued visual field, which spread to anterior scalp sites over time. After 500 ms post cue, negative potentials were more negative in right temporaal parietal sites regardless of cue direction. Peripheral cues enhanced the NI component (140–200 ms post cue) over the contralateral hemisphere. Following Nl enhancement, a sustained negative potential shift appeared after 460 ms post cue at posterior scalp sites contralateral to cued field and spread over the temporal and central regions. These results suggest that the neural processes underlying spatial selection are initiated in the posterior region and that other cortical activities are recruited in a serial fashion. Symmetrical early activation of each contralateral hemisphere suggest independent involvement of the hemispheres in the early stages of shifting attention toward the contralateral visual field. A predominant contribution of the right hemisphere to sustained spatial attention was demonstrated in the late stage of cue processing at the right temporal and parietal regions. Different ERP patterns generated by central and peripheral cues support the hypothesis that distinct neural systems are involved in voluntary and reflexive mechanisms of attention shift.

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