Figure 1.

Post-decision wagering behavior in monkeys is indicative of choice certainty. (A) The sequence of events in the task. After acquiring a central fixation point (small red point), two “direction targets” (large red spots) appeared on the screen, one inside the neural response field (RF; gray shading), the other on the opposite side of the screen. The motion stimulus appeared after a short delay, remained visible for 100–900 ms, and was followed by another delay (1200–1800 ms). On half of the trials (lower branch) the delay persisted until the fixation point was turned off, which served as a Go signal that instructed the monkey to indicate the perceived direction of motion by a saccadic eye movement to one of the “direction targets.” A correct response led to a liquid reward; a wrong response led to no reward and a brief timeout. On the other half of the trials (upper branch) a third target was presented 500–750 ms after extinction of the motion. Choosing this “sure target” (T_s; blue spot) led to a smaller reward (~80% of correct reward). On these trials the monkey could choose T_s or a direction choice. The two trial types were randomly interleaved. (B) The frequency of choosing T_s was greater when the motion strength (%coherence) was weak or the duration brief. The points are data grouped in duration quantiles (deciles). Error bars (SE) are smaller than the symbols. (C) Decision accuracy when T_s option was waived. The graph compares performance on trials in which T_s was not shown (open symbols, dashed curves) with trials in which T_s was offered but waived (filled symbols, solid curves).