Conservative Decisions Guided by the Anterior Cingulate Cortex

occur. In their task, subjects responded to target shapes (e.g., triangles) appearing in a stream of distractor shapes. The authors varied the likelihood with which any particular stimulus (or sequence of two stimuli) would be followed by a target. Since participants were not told about these regularities (and indeed failed to notice them during the experiment), predictive information was learned implicitly during each block. In an elegant analysis of reaction time distributions (Carpenter and Williams, 1995), the authors were able to test whether predictive information influenced the decision threshold, the accumulation rate of sensory evidence, or both. They found that more predictive information lowered the decision threshold but did not accelerate the rate of evidence accumulation, biasing participants to make faster responses when they were expecting a target shape on the basis of previous distractors. However, since all stimuli were easily discriminable, perceptual processes had likely reached asymptotic performance and could not be further improved by gain control mechanisms. When stimuli are harder to discriminate, predictive information may influence perceptual processing as well (Liston and Stone, 2008; Melloni et al., 2011). If predictive information lowers the decision threshold, any evidenceaccumulation brain region should respond less to targets when predictive information is high, but should respond more when the accumulation rate is fast. Only the right dorsolateral prefrontal cortex (dlPFC) had both response properties (their Figure 7), partially confirming previous findings in humans and monkeys that the dlPFC represents the amount of accumulated sensory evidence (Heekeren et al., 2004; Gold and Shadlen, 2007). Predictive information itself was negatively correlated with a large, distributed network. It consisted of the inferior frontal gyri, the right intra-parietal sulcus, the left and right dlPFC, and, most importantly, Conservative decisions guided by the anterior cingulate cortex