Figure 3.

Second-stage P300 and transition type. A, Grand average waveforms of rare and common trials stimulus locked to second-stage stimuli (aliens). Waveform is baselined −200 to 0 ms. The mean amplitude for stimulus-locked P300 was obtained over four centro-parietal electrodes [D16 (CP1), A3 (CPz), B2 (CP2), A4], as indicated by the white dots in the topography plot. This transition effect was no longer significant when the second-stage P300 signal was response locked (Fig. 3B). B, Topography plot represents the P300 component –100 to 0 ms before second-stage response. White dots indicate parietal electrode sites [A4, A5, A19 (Pz), A32] where the positive component was measured. Grand average second-stage P300 is plotted response-locked comparing the waveforms following rare versus common transitions. Single-trial analyses indicate that the P300 amplitude, measured as the mean amplitude −100 to 0 ms (shaded gray), does not distinguish transition type (β = −0.02, SE = 0.01, p = 0.23).