P300 and Tracking Difficulty: Evidence For Multiple Resources in Dual‐Task Performance

ABSTRACT Subjects performed a visual tracking task while performing a concurrent task in which tones were covertly counted. The P300 component of the event‐related potentials elicited by the tones was examined to determine the extent to which its amplitude was affected by variations in the forcing‐function bandwidth, or difficulty, of the tracking task. P300 decreased in magnitude when tones were counted in conjunction with the performance of the tracking task, relative to a single‐task counting condition. Increasing tracking difficulty failed to reduce P300 amplitude further. A second experiment obviated the possibility that movement‐related potentials caused the P300 attenuation resulting from the introduction of the tracking task. In Experiment 3, subjects performed a reaction time task in conjunction with tracking in order to establish the validity of the tracking difficulty manipulation. The results are interpreted in terms of a theory of functionally‐specific processing resources.