Fig. 2.

Phase-of-firing differences by stimulus category. (A) Population average of phase differences between categories, across time and frequency. The average F statistic taken from each single unit’s phase difference between face and object stimuli is displayed. Time on the x-axis indicates the center point of the 200-ms sampling window; frequency of oscillation is indicated on the y-axis. Significance was determined through permutation testing (Methods). Time-frequency points that failed to achieve significance at the population level are masked in gray, and the color map is capped at 10 for direct comparison with Fig. 3A. (B) Single spike–LFP example showing a difference in mean phase for faces and objects across time and frequency. Time-frequency points are masked if they fall within the 95th percentile of the category-shuffled distribution (Methods). The rate response of this example is shown in Fig. 1A, Left (middle trace). (C) Phase-dependent spike histograms (Upper), and the difference between the histograms from the face and object conditions (Lower). For each trial category, spikes were binned according to the phase of gamma in which they occurred for a given time window. Here the spike phase is shown for one of the peaks of phase angle difference seen in B: 46 Hz, 55 ms after image onset ± 100 ms). For clarity, the cycle is plotted twice (i.e., from 0 to 4π) and normalized by the grand maximum bin count across the two conditions.