Figure 1.

Task and behavioral results. A, Schematic of the dimensions task. Participants were presented with three different stimuli, each having a different feature along each one of the three dimensions (shape, color, and texture). Participants then selected one of the stimuli and received binary reward feedback, winning 1 (depicted) or 0 points. After a short delay, a new trial began with three new stimuli. B, Illustration of one game for one participant. Only the chosen stimulus is depicted for each of 10 consecutive trials, along with the outcome of each choice. C, Learning across games and participants, for games in the first 500 trials. Plotted is the percentage of choices of the stimulus that contained the target feature, throughout the games. Dashed line, chance performance; shaded area, SEM across participants. Learning in the 300 trials during functional imaging was similar, but the learning curve is less interpretable as games were truncated when a performance criterion was reached (see Materials and Methods). Other measures of learning, such as the number of trials to criterion (mean = 17.00 for the 500 fast-paced trials; mean = 16.40 for the slower-paced 300 trials; p = 0.09, paired t test), also suggest that performance in the two phases of the task was comparable. D, Percentage of games in which the stimulus containing the target feature was chosen on 0–6 of the last 6 trials of each game, across participants and games in the first 500 fast-paced trials (black) and in the last 300 slower-paced trials (white). In ∼40% of the games, participants consistently chose the stimulus that contained the correct feature (6 of 6 trials correct), evidencing that they had learned the identity of the target feature. In the rest of the games, their performance correct was at chance (on average, only two trials containing the target stimulus, consistent with the participant “playing” on an incorrect dimension and only selecting the stimulus containing the target feature by chance, that is, one-third of the time).