Fig. 1.

Experimental design. A, Baseline task: three pictures repeatedly appeared in the same order (1-2-3-… ) but were intermittently immediately repeated (*). Subjects were requested to detect these immediate picture recurrences.B, Activation task: five runs were composed from the same set of pictures, among which some were selected in each run to reappear once or twice during the run. Subjects were requested to detect pictures recurrences within, and only within, each run (*). Only the picture order changed from run to run; all other parameters (set of pictures, number of targets, etc.) were constant in all runs.