Fig. 9.

Comparison of the first 40 Hz component to the low-frequency P1 of the evoked response. The broad-band averaged evoked potential (thin line) of a typical subject is presented at two electrodes, superimposed with the 30–50 Hz filtered evoked potential (thick lines). The vertical barindicates stimulus onset. The oscillatory 40 Hz event occurs atC4, whereas the low-frequency P1 is rising at O2. Note the amplitude difference between the two events. The topographies of the 30–50 Hz and 0–25 filtered evoked potential are shown at three latencies: they are clearly distinct.