Figure 1.

Behavioral tasks. Participants performed both 2-AFC tasks. A, Visual task. Participants viewed two circular stimuli that were presented simultaneously to the left and right of fixation; one stimulus contained only visual noise, and the other contained a grating embedded in noise. Participants performed a 2-AFC judgment, indicating which stimulus (left or right) contained the grating. Subsequently, participants rated how confident they were that their 2-AFC judgment was correct using a 4-point scale (not shown on the screen). Participants were constrained to provide both responses within 5 s (see Materials and Methods). B, Memory task. At the beginning of each block of 50 trials, participants studied a list of words arranged in 10 rows and 5 columns (an 8 row × 3 column is shown here for ease of display). In each trial, participants viewed two words presented simultaneously to the left and right of fixation; one word had been presented on the study list and the other hand not. Participants performed a 2-AFC judgment, indicating which word (left or right) was on the previously studied list. Subsequently, participants rated how confident they were that their 2-AFC judgment was correct using a 4-point scale (not shown on the screen). Both responses had to be provided within 5 s.