Figure 2.

Behavior Was Influenced by the Base Rate

(A) Proportion of trials on which the participants reported rightward motion as a function of motion coherence. Data (symbols) are shown separately for the six levels of base rate, from 0 (leftward was the correct choice for all trials in the block) to 1 (all rightward), combining all stimulus durations and trials in the block. The solid lines are fits of a logistic regression model (Equation 19). The shift in the psychometric functions indicate that participants choices were influenced by the base rate. Inset shows the magnitude of the bias (${\beta }_3$, Equation 19) against the actual base rate (error bars are SE; most are smaller than the points; solid line is least-squares fit).

(B) Effect of motion strength and base rate on choice accuracy (same data as in A).The base rates (color) are combined by degree of informativeness.

(C) Average confidence reported on correct trials as a function of the motion coherence. The a priori probability of correct (color) is an expression of the base rate relative to the choice that is made (see text). Error bars represent SE across trials.

(D) Average belief as a function of trial number within a block for the six different biases. Same color convention as in (A). A belief of 0 or 1 indicates full certainty that the block was biased to the left or right, respectively. Shading indicates SEM. Data are combined across all participants. The same analyses for each participant are shown in Figure S1, and the distributions of confidence and belief for each subject are shown in Figure S2.