Fig. 1.

Working memory paradigm. Subjects were asked to remember the position of circles (d = 125px) that were presented at 20 pseudo-randomly chosen angles along a hidden radial grid (r = 415px). This was done to mimic the ‘ring’ structure of the biophysically-based computational model motivating the design (Compte et al., 2000). After a delay subjects used a high-sensitivity joystick to indicate the remembered location, providing a parametric index of accuracy (as opposed to a forced-choice yes/no answer). The delay period varied parametrically such that subjects were asked to hold the location in memory for 0 s (i.e. immediate recall), 5 s, 10 s, 15 s, or 20s (60–20 trials). Subjects also completed a series of trials that contained a distractor, such that an additional circle appeared that subjects did not have to remember. During the distractor task the delay period was always 10s and the distractor appeared in the middle of the delay (after 4.3 s). There were two types of distractors, appearing at either 20° (proximal distractors) or 50° (distal distractors) from the original cue position (40 trials each). Lastly, subjects completed a control motor task (not shown) where cue circle and probe circle appeared simultaneously, requiring subjects to place the probe on top of the cue circle which necessitated a motor response but no WM maintenance or recall (20 trials).