PUPILLOMETRIC ASSESSMENT OF COMPENSATORY EFFORT IN A MEMORY-SEARCH TASK UNDER PHYSICAL AND PHARMACOLOGICALLY-INDUCED SUBOPTIMAL STATES

Extensive research has shown that the phasic pupil size (peak level on each trial) is a sensitive measure of the degree of mental effort dem anded by a task. In the present study, the validity of the pupil respo nse as an index of mental effort in suboptimal conditions was investig ated. Thirteen males (19-29 years) performed a memory and display-sear ch task in a practice session, followed in random order by an oxazepam session, a placebo session, a physical exercise session, and a contro l session. After both oxazepam and physical exercise, decision times i ncreased, but pupil response increased only after physical exercise. T his result was explained by the possibility that under physical fatigu e, 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 insi ght into different effects of suboptimal states.