Disparity in spatial and temporal correlations persists after controlling for the noise effect.
A, B) Comparison of scan-wise spatial and temporal correlations (paired t-tests across individual scans. ***:p<0.005); C-G) Simulation to evaluate factors that affect apparent correlation values including contrast-to-noise ratio (CNR) and the number of data points C) Two fixed signals with the true correlation coefficient of 0.95 are simulated (10000 data points) with random noise at a given CNR level being added. This process is repeated 159 times (i.e. # of scans in our study) for each CNR level. At each CNR, the CC was calculated either based on the averaged signals from all 159 trials (i.e. denoised data, triangle dots in D-G), or on signals of individual trials (i.e. with-noise data, round dots in D-G) before the resulting correlations are averaged across trials. D) Simulated signals resampled to 1200 data points (equal to the number of time points used to calculate temporal correlations). E) Simulated signals resampled to 6157 data points (equal to the number brain voxels used to calculate spatial correlations). Importantly, we can replicate the difference between true (R = 0.95) and apparent (R = 0.58) correlations obtained from denoised data and with-noise data, respectively, when CNR = 1.3. Therefore, we estimate that the CNR of our BOLD data is ~1.3. F,G) The same process as C-E with the true correlation of 0.59. This true correlation value is obtained by iteratively setting different true correlation values and searching for the one that provides the trial-wise apparent correlation of 0.37 (as measured by the gamma-BOLD temporal correlation in our real data, Figs. 3A) at CNR = 1.3. F) Simulated signals resampled to 1200 data points. G) Simulated signals resampled to 6157 data points.