The P300 component of the event-related brain potential and mental effort

The P300 component of the ERP has been gaining importance as an index of information processing and cognitive activity and as a measure of workload. This study was conducted to test whether or not P300 reflects changes of effort accompanying a graduation of the task demand. The event-related brain potentials were elicited directly by task stimuli of a reference-task paradigm. Eleven healthy subjects had to detect omitted digits in tasks of randomly ordered digits varying in their number (categories I to V). Tasks of categories II to V were equiprobable (5% each) and embedded in a sequence of the reference tasks (I). The electroencephalogram was recorded from leads Fz, Cz, and Pz. Reaction time and rated effort confirmed a graduation of task demands from I towards V. The P300 amplitude increased from category II to V and was related linearily to the rated effort. It is proposed that an effort-contingent task evaluation on the basis of physical cues takes place.