Figure 1.

Experimental design. A, In the sequence learning experiments, participants saw a sequence of images in a fixed order, and were asked to learn the sequence order. The stimulus sequence consisted of five to seven image periods (image number fixed per session and determined by the availability of the patient) separated by ISI periods. Each image was presented for 1.5 s followed by an ISI of 0.5 s. The sequence was repeated for 60 loops. 20% of the time, a probe event occurred (black squares) during which participants had to decide which of two choice images was the correct one at the current position in the sequence. The probe events occurred at random positions of the sequence. After the probe event, the sequence resumed. In our main analysis, we consider time periods that occurred between two consecutive probe events as the trials of interest. As shown, each postprobe trial consisted of several image and ISI periods (gray squares). B, The design of experiment 2 was similar to that of experiment 1 except for the insertion of 10-s-long gap periods (black rectangle) during sequence learning. These gap periods occurred periodically (see below, Materials and Methods). During the gap periods, the sequence stopped, and patients were presented with a blank screen. They were asked to simply wait until the sequence resumed.