시각적 탐색에서 표적에 의해 유발된 N2pc 성분의 특성 및 측정

초록

This review aims to specify problems and to explain the reason why they occur when measuring event-related potentials (ERPs)--N2pc(N2 post-contralateral) component often used in recent studies of visual attention. For these purposes, an overview of N2pc measurement technique to observe an attention shift in visual search was provided, and several solutions for the problems were discussed. Presence of N2pc component is determined according to a more negative-going potential in EEG amplitude measured from the electrodes that are contralateral to the target than those ipsilateral, elicited about 200ms after the search array onset. Generally, the amplitude difference between the contra- and ipsilateral electrodes becomes maximal when attention shifts to the target location, and the moment of this attention shift can be sought by systematic tests of the amplitude and latency of N2pc component. N2pc measurement requires high signal-to-noise ratio, and this can be accomplished by minimizing any noise occurring when EEGs are initially recorded online. Eye movements to a target position can exaggerate the N2pc contra-ipsi difference and thus trials with saccades toward the target position are typically rejected rather than corrected. To minimize lateralized readiness potentials (LRPs) possibly evoked by any lateralized search target, it is recommended to use only one hand for responses while switching the hand across blocks to counterbalance handedness.

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