Condition-based non-parametric analysis.
For the neuronal analyses we focused on mixed-risk trials with and
without ambiguity in comparison to high- and low-risk trials. During
mixed-risk trials as compared to high- and low-risk trials in the
pure-risk block significant activation was observed in the left
parahippocampal gyrus (Table 1, Figure 2). In the ambiguity block
activations were present in the right inferior frontal gyrus IFG (BA 47)
for mixed-risk trials with high ambiguity compared to high- and low-risk
trials with high ambiguity (Table 2, Figure 3). For the same contrast
with low ambiguity, activity in the left supplementary motor area (BA 6)
and in the left posterior insula was significant (Table 2, Figure 4).
The contrast high versus low ambiguity showed a significant BOLD effect
in the mixed-risk condition. High compared to low ambiguity was
correlated with activations in the right inferior parietal cortex and
the left DLPFC in BA 9 (Table 2, Figure 5). As noted above, mixed-risk
trials under high ambiguity showed the highest amount of low-risk
decisions on the behavioral level.