Alpha phase, temporal attention, and the generation of early event related potentials

In the present study, we have investigated the influence of ongoing alpha phase on the generation of the P1 component of the visual ERP, recorded in a target detection task. Our hypothesis is that in trials where pre- or peristimulus alpha phase is already aligned in a way that voltage positive alpha peaks develop seamlessly into the P1, detection performance will be enhanced as compared to trials where alpha is not aligned. The findings supported our hypothesis and showed that target detection times for the subset of seamless alpha trials was significantly shorter than for trials that are not seamless. Our findings contradict the evoked model for the generation of early ERP components, which rests on the assumption of fixed latency, fixed polarity components. We found that in the non-seamless trials the 'candidate' component of the single trial P1 was at the opposite polarity. Despite this fact, alpha phase locking was at the same high level as was observed for the seamless trials. Finally, we found that prestimulus alpha phase was aligned already in a time window preceding the P1 by 400ms.