Fig. 3.

Event-related phase/amplitude coupling modulated by task demands. Trial-by-trial variance in low frequency phase explains a significant amount of the trial-by-trial variance in γ amplitude in visual cortex in response to (a) attended non-target standard and (b) attended target stimuli (data are from the same electrode as in Figure 1). (c) Traditional PAC for a priori α/γ coupling across the first 250 ms post-stimulus onset shows no significant difference between non-targets (blue) and targets (red). Note the lack of temporal resolution because PAC is calculated across time and averaged across trials. In contrast, ERPAC (d) is calculated across trials on a point-by-point basis in the time series. This shows that PAC in response to targets (red) is significantly higher compared to non-targets (blue) during the same 250 ms post-stimulus time window where traditional PAC showed no differences (black dots above ERPAC traces denote time points with a significant PAC difference between stimuli at p < 0.01; see Methods).

Error bars indicate SEM. (n.s.), not significant (p = 0.14)