Oculo-Cognitive Addition Test: Quantifying Cognitive Performance During Variable Cognitive Workload Through Eye Movement Features

The need exists for a device that can rapidly and accurately assess cognitive impairment. Because the link between oculometrics (i.e., eye movements) and cognition is well-documented, the Oculo-Cognitive Addition Test (OCAT) was developed which tracks eye movements as the user completes a simple mental addition test. OCAT consists of 12 trials of summing three consecutive single-digit numbers, shown separately on three consecutive screens. The first, second, and third screens in each trial correspond to low, medium, and high cognitive workloads. Using an infinity-loop pattern of 24 symmetrical positions not evident to the subject, eye movements were captured systematically in horizontal, vertical, and diagonal directions. Cognitive impairment was simulated by exposing subjects to 5 minutes of a hypoxic gas mixture (8% O-2 + 92% N-2). 20 subjects completed OCAT at baseline (i.e., normal room air), hypoxia, and post-baseline (i.e., breathing 20 minutes of room air) conditions. Raw scan-paths were collected with an eye-tracking device. Oculometrics pertaining to fixations and saccades were extracted. OCAT completion time significantly increased from baseline to hypoxia, which corresponded to a significant decrease in cerebral oxygenation from baseline to hypoxia. From baseline to hypoxia, saccadic latency significantly increased while saccadic velocity significantly decreased in the diagonal direction. However, results in the horizontal and vertical directions were not significant. Fixation time significantly increased from baseline to hypoxia at medium and high cognitive workloads but did not significantly change at the low cognitive workload. From baseline to hypoxia, fixation size did not significantly change in any cognitive workload, however, the fluctuation in fixation size significantly increased at the medium cognitive workload. From baseline to hypoxia, the fixation area significantly increased in low cognitive workload, and the fluctuation in fixation area significantly increased at the high cognitive workload. OCAT can detect subtle changes in oculometrics that correlate with cognitive impairment. This study provides a rationale for providing varying cognitive loads to elucidate subtle changes in oculometrics that may otherwise go undetected in neurocognitive tests that do not vary the cognitive load.