Structural MRI, mask and functional activation.

<p>(<b>a</b>) Structural region-of-interest (white) on the subjects' average anatomical image. For visualization, black blobs exceed the 0.05 level uncorrected threshold corresponding to a Student's <i>t</i> (13 df). See the main text for statistical inference at a corrected p<0.05 level. (<b>b,c</b>) Whole brain analysis of the effect of ambiguity. (<b>b</b>) Shows a glass-brain view (maximum intensity projection) of significant activations. (<b>c</b>) Shows the anterior activation, which included right anterior hippocampus and amygdala as defined, superimposed on the subjects' average anatomical image. (<b>d</b>) The observed fMRI trial-by-trial time-series (blue) averaged over all subjects for the hippocampal activation identified in our whole brain analysis (see main text). The model-based ambiguity is shown in red. Note that the model only captures the slow changes in observed responses over blocks as the contingencies are learned.