INTERACTION OF ODDBALL PROBABILITY AND PRIMARY TASK TYPE ON P300 IN THE DUAL-TASK PARADIGM

Using a dual-task paradigm with an oddball secondary task, P300 amp an d latency were studied as a function of factorially manipulated oddbal l probability (low = .22, high = .44) and primary task type. In additi on to a Baseline condition (oddball task only), three primary tasks we re used: (1) Pure Sensory; watching a movie; (2) Pure Motor (manipulat ing a flashlight); and (3) Sensory/Motor (using the flashlight to trac e the outlines of characters in a movie). The findings included the us ual significant effects of probability on amplitude. There was also a significant effect of task type on amplitude, and a significant intera ction of oddball probability with task type. In the low but not high p robability condition, a pure Sensory task depressed P300 amplitude. In both probability conditions, the Sensory/motor task depressed P300 am plitude. Only task type had a significant effect on P300 latency. The results confirm the ability of other labs (using Sensory/motor primary tasks) to demonstrate P300 depression at high oddball probability, in view of the difficulty in our lab of achieving P300 depression with p ure sensory tasks and high oddball probabilities. The results are disc ussed in terms of partial overlap of processing resource pools.