Author(s): VON HERTLEIN, D., LABORDE, S., SCHIPKE, J., WOLFF, K., VOGT, T., MÖLLER, F., Institution: GERMAN SPORT UNIVERSITY COLOGNE, Country: GERMANY, Abstract-ID: 645

INTRODUCTION:
Critical Flicker Fusion Frequency (CFFF), defined as the threshold at which a blinking light is seen as constant, is discussed as a diagnostic tool for rapid cognitive function (CF) assessments in clinical¹, psychological², and extreme environmentalᵌ settings.
However, the effects of environmental factors on the validity of CFFF are still poorly understood⁴.
Performance assessment in underwater and spaceflight contexts would benefit from fast and valid cognitive diagnostics to assess task readiness and determine further procedures, but environmental factors like changing illumination, immersion, or weightlessness, and altered ambient and inspiratory gas pressures might act as moderators. Furthermore, environmental conditions might affect vagus nerve activity, which is known to interact with cognition.
We hypothesised that (I) different environmental conditions (Water immersion, bright light, darkness, elevated inspiratory oxygen pressures (PᵢO₂) and their combination) would alter CFFF and (II) that transcutaneous vagus nerve stimulation (tvns) would positively affect CFFF.
METHODS:
CFFF was assessed in 19 subjects (Age:23.8+2.9;10 females) in the conditions Illumination (Bright/Dark), Immersion (Land/Underwater), and PᵢO₂ (0.56/1.4 bar) in a crossover design. In a different cohort, 18 participants (Age:23.6+2.3;12 females) conducted the same CFFF tests after either tvns (NEMOS) or a sham condition. HRV was recorded using an ECG (Bittium Faros).
Paired samples t-tests were conducted on the factors Illumination, Immersion, and PᵢO₂ in the 1st cohort and separately for the effects of tvns in the 2nd cohort. Effect sizes are displayed as Cohen’s d.
RESULTS:
A significant effect was observed for illumination outside on land (p=.028, d=.467; Bright: 36.47Hz, Dark: 35.84Hz). Main effects were also observed for immersion during Bright (p=.009, d=.593/Land: 36.28Hz, Underwater: 37.9Hz) and Dark illumination (p=.045, d=-.412/Land: 36.38Hz, Underwater: 37.3Hz). Tvns showed no effects on CFFF (p= .112, d=-.218/tvns: 35.4Hz, sham: 35.0Hz).
CONCLUSION:
Despite the effects of illumination and immersion, the small absolute differences do not suggest a major impact on CFFF validity. A potential explanation for the effect of illumination on CFFF is the eye’s adaptation changes to ambient light⁴. No direct influence of autonomic stimulation on CFFF was observed, supporting robustness for an application in extreme environments. Future work might focus on the link of CFFF to executive function and operational performance in extreme environments and sports contexts to increase safety for planning and decision-making.

¹Fu et. Al (2021). DOI: 10.1016/j.aopr.2021.100011
²Curran & Wattis (2000). DOI: 10.1002/(SICI)1099-1077(200003)15:2<103::AID-HUP149>3.0.CO;2-7
ᵌLafère et. Al (2019). DOI: 10.28920/dhm49.2.119-126
⁴Schipke et. al (2023). DOI: 10.3390/medicina59040800