Figure 1. Timeline of an experimental trial.

Participants were asked to maintain in memory the orientation of a memory cue (grating); at the end of each trial they were asked to indicate whether a test probe was tilted to the left or to the right relative to the memory cue. In addition, participants provided a confidence rating for this memory jdugment by using a scale from 1–9 (1 = not confident at all; 9 = extremely confident). On 75% of the trials, the first memory cue was followed by a second cue; this could be either identical to the first cue, or its orientation differed by 10 or 40 degrees. In the active condition, participants were asked to hold its orientation in memory. Thus in this condition, participants were required to hold the orientation of two cues on each trial. The maintenance of the 2^nd cue was assessed in the same manner as that of the 1^st cue: they were asked to indicate whether a test probe was tilted to the left or to the right relative to the memory cue. The memory judgment relating to the 2^nd cue was always made after the two responses (accuracy and confidence responses) relating to the first cue. In the passive condition, participants were not required to hold the 2^nd cue in memory. To ensure that they attended to the 2^nd cue, participants were asked to indicate at the end of the trial whether or not the 2^nd cue was presented.