Fig. (1).

In 15-s blocks (alternating with 15-s baseline with no stimuli), the subjects were presented with broadband noise bursts (gray circles; duration 100 ms) with varying pitch and Gabor gratings with varying orientation in four (left and right ear, above and below fixation) concurrent, independent and asynchronous streams (within stream onset-to-onset interval 200–400 ms). In the auditory tasks, the subjects selectively attended to sounds presented to the left ear and ignored the input to the right ear or vice versa. In the visual tasks, the subjects selectively attended to Gabor gratings presented above fixation and ignored the pictures below fixation or vice versa. Throughout the experiment, subjects focused on a fixation mark which also indicated the current task. For example, an arrowhead pointing up instructed the subjects to attend to Gabor gratings presented above fixation.