Suggested Caption:
NEEMO 13 aquanaut, astronaut Richard Arnold, performs the Psychomotor Vigilance Test (PVT), a three-minute test which measures vigilance, attention and psychomotor speed. The PVT is taken at least four times a day — on waking, before and after simulated moon walks, dives and habitat experiments, and before bed.

Suggested Caption:
During NEEMO 12, veteran astronaut Heidemarie Stefanyshyn-Piper is shown with a Psychomotor Vigilance Test (PVT) device. Also visible on the table is a clear bag for the daily saliva samples, which are used to measure cortisol, a hormone that provides information on stress levels.