BACKGROUND: PERCLOS is a metric that has been primarily studied in the domain of driver fatigue to predict performance decrements, but there is comparatively less research applying it to aviation, where hypoxia is a safety concern. Hypoxic exposure was expected to increase blink activity, possibly by means of impairing blink inhibition behavior, thereby leading to increased eyelid closure time.METHODS: PERCLOS, blink rate, and blink duration were measured using head-mounted eye-tracking on pilots using a flight simulator inside a hypobaric chamber. Pilot subjects were tasked with programming the autopilot of a G-1000 console according to instructions from a simulated air traffic controller. Data was collected at 5% decrements in blood oxygen saturation (S_po₂) through progressive decreases in hypobaric pressure to model slow-onset hypoxia.RESULTS: PERCLOS, blink rate, and blink duration increased significantly and linearly as a function of decreasing S_po₂, and largely recovered in the posthypoxia normoxia condition. The greatest change in PERCLOS relative to the prehypoxia baseline occurred in the 80% S_po₂ condition, whereas the greatest change in blink rate and duration occurred at 75% S_po₂. As S_po₂ decreased, a higher frequency of long blink durations was observed.DISCUSSION: The increase in blink rate and duration in the absence of task demand manipulation could suggest hypoxia-induced sympathetic excitation and impairment of adaptive blink inhibition behavior. The effect of hypoxia on oculomotor features is also likely task-specific. In consideration of the extensive demand made upon the visual modality in flight, increased PERCLOS may further tax visual information processing.Thropp JE, Scallon JFV, Buza P. PERCLOS as an indicator of slow-onset hypoxia in aviation. Aerosp Med Hum Perform. 2018; 89(8):700–707.