# Complex Relationship Between Critical Flicker Fusion Frequency and Established Cognitive Tests Unveiled by Hyperbaric Exposure

## TL;DR

This study shows that a visual flicker test can detect brain function changes under pressure, but it only predicts recovery time when breathing air, not nitrogen-free gases.

## Contribution

The study reveals that flicker test recovery patterns differ based on breathing gas, offering new insights for dive safety and cognitive readiness.

## Key findings

- CFFF increased under pressure but only remained elevated after air breathing.
- CFFF and cognitive tests showed weak correlations, indicating they measure different brain functions.
- Nitrogen-free gases allowed faster recovery of CFFF compared to air.

## Abstract

Divers and people working in pressurized environments often experience changes in their ability to think clearly and react quickly. To ensure safety, we need simple tools that can quickly assess whether someone’s brain is functioning normally under these challenging conditions. This study examined whether a rapid visual test called the “flicker test”, which measures how fast a person can detect changes in flickering light, could serve as a practical indicator of cognitive performance when people breathe different gas mixtures in a pressure chamber simulating a 30 m dive. We tested 40 healthy adults three times, each time with a different breathing gas: atmospheric air, a helium–oxygen mixture, and a helium–oxygen–nitrogen mixture. We found that pressure increased flicker test scores regardless of the gas breathed, but only while breathing air did the scores remain elevated after returning to normal pressure. The flicker test results showed weak correlations with cognitive performance tests, suggesting they measure somewhat different aspects of brain function. These findings indicate that people breathing air may need more recovery time before resuming demanding cognitive tasks after diving, while nitrogen-free gases allow faster return to baseline brain function, which has important implications for dive planning and post-dive work protocols.

Critical flicker fusion frequency (CFFF) has been proposed as a rapid marker of central nervous system arousal state, but its relationship to cognitive performance under hyperbaric stress remains unclear. Forty healthy adults (20 women; age 19–46 years) underwent three hyperbaric exposures at 4 ATA (equivalent to 30 m seawater depth) while breathing air, heliox, and trimix in randomized order. CFFF and cognitive performance (Simon task, Digit Span, Corsi Block-Tapping) were assessed before compression, at 4 ATA, and after decompression. Both CFFF and reaction times increased modestly at 4 ATA across all breathing gases (3–5% elevation, p < 0.05). Following decompression, however, these measures showed divergent recovery patterns: CFFF normalized completely after heliox and trimix, but remained partially elevated after air breathing. In contrast, reaction times improved substantially after decompression (10–15% faster than baseline) regardless of breathing gas, reflecting practice effects. Weak correlations emerged between specific CFFF components and executive cognitive measures, while memory performance remained stable throughout all conditions. CFFF and cognitive performance exhibit some parallel increases under hyperbaric stress but most likely capture largely independent aspects of neural function. Breathing gas composition selectively influences CFFF recovery dynamics, with nitrogen producing prolonged neural effects relevant for assessing post-dive cognitive readiness.