Assessing Critical Flicker Fusion Frequency: Which Confounders? A Narrative Review

Abstract

The critical flicker fusion frequency (cFFF) refers to the frequency at which a regularly recurring change of light stimuli is perceived as steady. The cFFF threshold is often assessed in clinics to evaluate the temporal characteristics of the visual system, making it a common test for eye diseases. Additionally, it serves as a helpful diagnostic tool for various neurological and internal diseases. In the field of diving/hyperbaric medicine, cFFF has been utilized to determine alertness and cognitive functions. Changes in the cFFF threshold have been linked to the influence of increased respiratory gas partial pressures, although there exist inconsistent results regarding this effect. Moreover, the use of flicker devices has produced mixed outcomes in previous studies. This narrative review aims to explore confounding factors that may affect the accuracy of cFFF threshold measurements, particularly in open-field studies. We identify five broad categories of such factors, including (1) participant characteristics, (2) optical factors, (3) smoking/drug use, (4) environmental aspects, and (5) breathing gases and partial pressures. We also discuss the application of cFFF measurements in the field of diving and hyperbaric medicine. In addition, we provide recommendations for interpreting changes in the cFFF threshold and how they are reported in research studies.

Comment on Muth et al. Assessing Critical Flicker Fusion Frequency: Which Confounders? A Narrative Review. Medicina 2023, 59, 800

“…We agree with Muth et al [ 1 ] that the state of knowledge about CFFF still has many gaps and ambiguities. Possibly, an international cooperation involving key research teams exploring the intricacies of flickering light could represent an important step toward developing general protocol standards.…”

“…We first want to thank the authors of the excellent review for their contributions to summarizing the confounders associated with critical flicker fusion frequency (CFFF) [ 1 ]. We read this review with great interest as the publication significantly broadened with this aspect of the summary we wrote [ 2 ].…”

“…They pointed out that the sensory functions and processing speed, used in the flicker test, may be relevant to executive functions, but it is possible that the CFFF scores were correlated with stronger brain connectivity (as efficient executive functions also require this) [ 7 ]. As Muth et al [ 1 ] justify, the reduction in retinal illumination may impact the lower CFFF threshold in older people compared to the young ones [ 8 ], but in view of explanations provided by Mewborn and colleagues [ 6 ], we might also expect that these differences were the result of brain connectivity deteriorating with age [ 9 , 10 , 11 ]. So what connectivity networks are involved in flickering light processing?…”

The speed of sight: Individual variation in critical flicker fusion thresholds

“…As variation between individuals of the same species is present in many aspects of visual perception, we aimed to evaluate whether this is also the case for critical flicker fusion thresholds, using healthy human participants. CFF has been well studied in humans, and previous research has found that critical flicker fusion thresholds are affected by many physiological factors [ 10 ]. For instance, different parts of our retina have different levels of sensitivity to flicker [ 11 , 12 ].…”

Reply to Mankowska et al. Comment on “Muth et al. Assessing Critical Flicker Fusion Frequency: Which Confounders? A Narrative Review. Medicina 2023, 59, 800”

“…First and foremost, we like to express our gratitude for the praise bestowed upon our narrative review [1], particularly as it comes from a group of such esteemed reputation [2].…”