Fig. 1.

Experimental design. a Sixteen blocks of trials were each preceded by an arbitrary task difficulty label, presented to influence expectations about task difficulty. Twelve trials per block included a jittered fixation (1–6 s), stimulus presentation/response period (4 s), and immediate presentation of positive or negative feedback (1 s). b Within each block of trials, 12 distinct figures from two different families would appear in random order. Members of one family were associated with the first button on the button box, while members of the second family were associated with the second button. During the next block, members from two new families would be randomly presented