Pupillometric assessment of compensatory effort in a memory search task under physical and pharmacologically-induced...

Extensive research has shown that the phasic pupil size (peak level on each trial) is a sensitive measure of the degree of mental effort demanded by a task. In the present study, the validity of the pupil response as an index of mental effort in suboptimal conditions was investigated. Thirteen males (19-29 years) performed a memory and display-search task in a practice session, followed in random order by an oxazepam session, a placebo session, a physical exercise session, and a control session. After both oxazepam and physical exercise, decision times increased, but pupil response increased only after physical exercise. This result was explained by the possibility that under physical fatigue, compensatory effort was exerted, whereas under drug-induced fatigue, subjects seemed unable to compensate for the performance decrement. The pupil response appears to be a valuable tool for gaining more insight into different effects of suboptimal states.