Figure 1.

The STWM task. Each session consisted of alternate presentations of pairs A, B, and C. The first three trials with each pair were acquisition trials (both arms rewarded). Each of the following trials was at the same time an acquisition trial (for the following trial with the same pair) and a test trial (for the arm visit made during the preceding trial with the same pair); the rewarded arm was the one that has not been visited on the preceding trial with the same pair. Memory demand varied across successive trials according to the retention interval (i.e., the number of intervening trials with other pairs between two successive presentations of the same pair). Three retention interval levels were distinguished: short (0 intervening trial), medium (1–2 intervening trials), and long (3–4 intervening trials). Organizational demand varied across trials according to proactive interference level [i.e., the number of intervening trials between the to-be-remembered trial (n-1) and the interfering trial (n-2): the more trials between them, the lower the proactive interference effect]; two proactive interference levels were distinguished: low PI (3–4 trials between n-2 and n-1) and high PI (0–1 trial between n-2 and n-1)