Relationship between the amplitude of alpha waves and reaction time

The amplitude of alpha waves in an ongoing electroencephalogram can be reduced by visual stimuli and by attention. We reduced alpha amplitudes by presenting a short visual stimulus in the visual periphery, 10 degrees apart from the fovea, and measured (i) the decrease of alpha amplitudes as a function of time and (ii) delays in reaction to foveal stimuli presented at various intervals after the peripheral stimulus. It turned out that in the time window from 0 to 2 s after the peripheral stimulus, both responses decrease in parallel with a minimum at 350-500 ms. The close correspondence between alpha amplitude and reaction time supports the view that alpha waves are functionally relevant for this behaviour.