As there were only two possible new rule sets after a switch, both correct and incorrect feedback were equally informative: a correct outcome indicated that participants should keep using the chosen response rule whereas incorrect implied they should switch to the other possible set. Therefore, in contrast to work which has emphasised the importance of the ACC for processing errors (Brown and Braver, 2005; Holroyd and Coles, 2002; Ullsperger and Von Cramon, 2003), it is interesting to note that activity in the ACC was identical in the GENERATE+MONITOR condition regardless of whether the feedback was positive or negative, suggesting that it is the salience of the information gained from the outcome that is driving the change in signal. This concurs with electrophysiological studies in monkeys which show that both receipt and withholding of reward can drive ACC neurons (Amiez, Joseph and Procyk, 2006; Matsumoto, Suzuki and Tanaka, 2003; Niki and Watanabe, 1979; Procyk, Tanaka and Joseph, 2000). Moreover, in spite of some differences between participants' reaction times on the first trial after a switch cue compared to that after a
