Fig. 4.

Specificity and latency of dva and the LPP. In this figure we compare the specificity of dva and the LPP to the “seen – unseen” dimension and also compare the latency of the peak difference in dva (seen − unseen) with that of the LPP. (A) Evoked potential at parietal EEG electrode Pz and (B) within-trial directional variance for seen face (gray) and seen house (black) stimuli at maximum color contrast. The LPP, which is higher in amplitude for seen versus unseen subjective reports, is also significantly higher in amplitude for face versus house stimuli (A). Gray and black stars at the bottom of the panel indicate time points where the difference is greater than chance at P < 0.05 and P < 0.01, respectively (corrected for temporal nonindependence). No significant differences between face and house stimuli were found for within-trial directional variance (stability, B), suggesting that stability is a more specific indicator of a positive subjective report. (C) Amplitude-normalized time course of the difference potential at electrode Pz (P300, gray) and the difference in directional variance, seen – unseen object. The difference in the latency of the peaks was 140 ms (P < 0.01, two-sided signed-rank test; Materials and Methods). (D) Scatter plot of the time of peak difference between evoked potentials at Pz, versus the time of peak difference in directional variance (each circle is one subject, n = 12). Gray cross shows the mean and SE of both variables. The peak stability effect follows the peak difference in the LPP, consistent with the notion of the LPP as an “ignition” event, the outcome of which is a transient period of relative stability of perceptual information.