Fig. 1.

Schematic representation of the visual stimuli (upper part) and trial sequence (lower part) in the single- and dual-task conditions. Note that the key difference between single- and dual-task conditions is the appearance of the central distractor stimulus in the dual-task condition, containing 1, 2, or 3 to-be-identified digits (for the 1-, 2-, and 3-distractor groups, respectively). In the single-task condition there is no distractor stimulus; here the neutral fixation sign (+) continues to be visible for the same duration as the distractor stimulus (i.e., 29 ms)