Figure 1.

Illustration of the reference-back task. In each trial, subjects indicate whether the probe stimulus (‘X’ or ‘O’) is the same as or different to the stimulus in the most recent red frame (the WM referent). In reference (red frame) trials, subjects must update WM with the currently displayed probe item. In comparison (blue frame) trials, subjects make the ‘same/different’ decision but do not update WM. Comparing behavior (e.g., accuracy, RT) between different trial types measures the costs of several WM control processes (see the main text and Table 1 for details).