BOLD response functions as predicted by the working memory and difficulty hypotheses.

<p>Figure 1 illustrates hypothesised BOLD response functions. The BOLD response in sub-regions of the frontoparietal network could be predicted according to one of two distinct hypotheses. If a frontoparietal brain region tunes to represent the current task set, then a BOLD response function relating to the probability of positive identification should be observed (similarity to target; black). Alternatively, if a frontoparietal brain region is recruited during increased cognitive demand, then a function related to distance from the 50% target/distractor decision boundary, where the target-distractor discrimination is at its most ambiguous should be observed (ambiguity; grey). To mimic conditions in the current experiment (see later), here the decision boundary is drawn close to the target.