QUANTIFICATION AND STATISTICAL ANALYSIS

All statistical tests were based on the combined data from both animals, constituting a fixed-effect analysis that results in inferences limited to the investigated sample of two animals. To lend equal weight to each animal, data were first combined within each animal (across sites, site pairs, trials) and subsequently averaged over the two animals. All significance thresholds were computed using non-parametric permutation statistics (Maris and Oostenveld, 2007). For the median split analysis, the observed PPC spectra were derived by 1) calculating PPC spectra across all epochs of a given condition in a given animal, separately for all V1-V4 site pairs, 2) averaging PPC spectra across those site pairs, and 3) averaging across the two animals after aligning the peaks of the respective frequency bands. Surrogate distributions were then generated by randomly distributing epochs in two conditions, maintaining the sample sizes of the original conditions (short RTs versus long RTs) (Maris et al., 2007). Then, the same steps as for the observed PPC spectra were followed. For each of 1000 randomizations, the maximal absolute difference value across all frequencies was retained and placed into the randomization distribution. The observed differences were compared against the distribution of maximal absolute differences. This procedure corrects for multiple comparisons across frequencies. A similar approach was used in the phase relation analysis. A surrogate distribution was generated under the hypothesis that there is no correlation between RTs and the preceding phase relation between V1 and V4. So, in each randomization, the correlation coefficients were calculated on randomly shuffled RTs. The observed coefficients were then compared against the surrogate distribution of maximal absolute coefficients.