Figure 1.

Post hoc scan-by-scan analyses were performed on brain regions identified as having significant MR signal change with the omnibus ANOVA for correct trials. Each 6-sec scan consisted of four behavioral trials, so the four trials were collapsed and averaged. In order for the MR signal to stabilize within an experimental condition (valid vs. invalid condition), scans containing the trial type of interest [compatible (C) or incompatible (I) trials] were preceded by at least one scan of all four compatible trials (valid condition) or all four incompatible trials (invalid condition). Thus the scans of interest consisted of four compatible trials preceded by four compatible trials (A); two compatible trials preceded by four incompatible trials (B); four incompatible trials preceded by four incompatible trials (C); and two incompatible trials preceded by four compatible trials (D). Scans that were analyzed (indicated by the arrows) consisted of those occurring 6 sec after the scan of interest to adjust for the typical 5- to 6-sec delay in peak of the hemodynamic response.