Fig. 2.

Functional connectivity analysis on residual data. (A) Residual data (blue, Y_R) not influenced by the main effect of stimulation were obtained for each visual quadrant from the fMRI data (green, Y_M) by subtraction of the data as estimated (modeled) by spm2 (pink, Y_E). Data were collected selectively for each attention condition and time-shifted by five images to account for the hemodynamic delay (see Materials and Methods). (B) Residual signal in two quadrants of V1 when both were attended (black) or unattended (red; data for one participant). The correlation was decreased in the unattended condition. (C) Average correlation coefficient (across participants) between quadrants that were both attended (black) or unattended (red). V1↔V1 and V2↔V2 refer to within-region correlation, and V1↔V2 refers to correlation between V1 and V2. The correlation between quadrants was significantly decreased when they were both unattended. Note that this change in correlation cannot be a consequence of differences in the main effects, because these differences were removed. Furthermore, the extraction of residuals is time-delayed by five images to avoid contamination by fMRI transients at the onset and offsets of each block. As a result, the residual signals showed no significant difference in variance under attended and unattended conditions ( and ; T = 1.17; P = 0.15).