Fig. 3.

Experiments 4–6. A–E, Experiment 4: gender judgment task. F–J, Experiment 5: emotion judgment task. K–O, Experiment 6: wealth judgment task. A, F, K, Task. A question prompt was presented for 500 ms, followed by the stimulus. Subjects were instructed to respond as quickly as possible, and the stimulus stayed on the screen until subjects responded. B, G, L, Confidence ratings (CR). Confidence ratings systematically varied as a function of stimulus ambiguity for the emotion judgment task but not for the gender judgment task nor wealth judgment task. C, H, M, RT. RT can be considered as an implicit measure of confidence, and had a similar pattern as confidence ratings. D, I, N, ERP at the electrode Pz. Gray shaded area denotes the LPP interval. E, J, O, Mean LPP amplitude. Error bars denote one SEM across subjects. Paired t test between adjacent levels of ambiguity: +, p < 0.1; *, p < 0.05; **, p < 0.01; ***, p < 0.001; n.s.: not significant. P, Mean confidence rating for each experiment. Q, Difference in confidence rating between anchor and high-ambiguity stimuli for each experiment. R, Mean RT for each experiment. S, Difference in RT between anchor and high-ambiguity stimuli for each experiment. T, Mean LPP averaged across all conditions for each experiment. U, Difference in LPP between anchor and high-ambiguity stimuli for each experiment. Error bars denote one SEM across subjects. Paired t test between subjects: +, p < 0.1; *, p < 0.05; **, p < 0.01; ***, p < 0.001; n.s., not significant.