Frequency-Dependent Light Stimulation Effects on Performance During Vigilance Tasks on a Laptop

Students, office workers, or other computer and mobile device users can suffer from decrements in alertness or productivity, but many intervention methods on these can be too distracting or even affect daily routines. Using heart rate (HR) to determine a fast and slow target frequency at which to oscillate light brightness stimulation on a laptop, thirty-six participants joined a cognitive task where we hypothesized that fast frequency stimulation would increase alertness and decrease relaxation, while slow frequency stimulation would have the opposite effects. We found that slow frequency stimulation produces a statistically significant delay in response time, users react more slowly (3.8e2 +/- 5.5e1 ms), when compared to the no stimulation (3.7e2 +/- 4.1e1 ms) (p = 9.0e-3) conditions. The (Slow - No Stimulation) response time (1.7e1 +/- 2.7e2 ms) produced a statistically significant delay in response time versus the (Fast - No Stimulation) response time (-0.74 +/- 2.4e1 ms) (p =.016). These delays due to slow stimulation occurred without influencing accuracy or subjective sleepiness ratings. We observed that frequency-dependent light stimulation can potentially influence HRV metrics such as the mean normal-to-normal intervals and mean HR. Future work will target breathing rate to determine light stimulation oscillations as we further investigate the potential of using the slow-frequency domain to unobtrusively influence user performance and physiology.