Figure 1.

Subjective Report of Decision Termination in a Perceptual Task

(A) Controlled-duration task. On each trial, participants fixated a central fixation point (FP). A random dot motion stimulus then appeared at the same time as a central clock started rotating. Participants were asked to judge the direction of motion (left versus right) and also the position of the clock hand at the time they made their decision. After a computer-controlled time (0.2–0.8 s), the motion stimulus was extinguished, and after a delay (0.2–0.8 s), a tone sounded and participants indicated the perceived motion direction by moving the cursor to one of two choice targets. They then reported their subjective decision time by moving a stylus to position the clock hand at the remembered clock location at the time of their decision about the motion direction (see STAR Methods, Methods S1 and S2, and Figure S1).

(B) Information flow diagram showing visual stimulus and hypothesized events leading to a decision. The visual stimulus gives rise to a decision variable (black trace) that is the accumulation of noisy evidence. The decision is complete when a “right” or “left” bound is crossed (that is, when ±B of evidence has accumulated). The example illustrates a trial that gives rise to a rightward choice with decision time around 500 ms, although the stimulus lasts 800 ms. Data from neural recordings [16, 19] suggest that the delay from motion onset to the beginning of the accumulation (t_s) is around 200 ms. In general, the reported subjective decision time (t_SD) might differ from the actual moment of decision termination by additional delays attributed to perceptual and cognitive operations associated with storage and recall of the clock position.