Resource reciprocity: an event-related brain potentials analysis.

The amplitude of the P300 component of the Event-Related Potential (ERP) has proven useful in identifying the resource requirements of complex perceptual-motor tasks. In dual-task conditions, increases in primary task difficulty result in decreases in the amplitude of P300s elicited by secondary tasks. Furthermore, P300s elicited by discrete primary task events increase in amplitude with increases in the difficulty of the primary task. The reciprocity in P300 amplitudes has been used to infer the processing tradeoffs that occur during dual-task performance. The present study was designed to investigate further the P300 amplitude reciprocity effect under conditions in which primary and secondary task ERPs could be concurrently recorded within the same experimental situation. Forty subjects participated in the study. Measures of P300 amplitude and performance were obtained within the context of a pursuit step tracking task (the primary task) performed alone and with a concurrent auditory discrimination task (the secondary task). Primary task difficulty was manipulated by varying both the number of dimensions to be tracked (from one to two), and the control dynamics of the system (velocity or acceleration). ERPs were obtained from both secondary task tones and primary task step changes. Average root-mean-square (RMS) error estimates were also obtained for each tracking condition. Increased primary task difficulty, reflected in increased RMS error scores, was associated with decreased secondary task P300 amplitudes and increased primary task P300 amplitudes. The increases in primary task P300 amplitudes were complementary to the decrements obtained for the secondary task, supporting the hypothesis of reciprocity between primary and secondary task P300 amplitudes across different manipulations of primary task difficulty.