ArXiv paper: Flicker fusion threshold is a falsifiable boundary of brain plasticity

In a 44-page review posted to ArXiv (q-bio.NC, paper 2607.29068), neuroscientist Natalia D. Rydzenska and colleagues from Poland tackle a fundamental puzzle: why do some perceptual abilities refuse to improve no matter how much you train them? Their answer centers on critical flicker fusion frequency (CFFF), the point at which a flickering light perceptually fuses into a steady glow. CFFF is notoriously stable within individuals across adulthood, even though the same visual cortex pathways handle spatial processing that remains highly trainable.

The authors propose a hierarchical model where CFFF marks a hard boundary between plastic and non-plastic systems. They systematically evaluate peripheral, thalamocortical, and cortical explanations, concluding that CFFF stability emerges from convergent constraints across processing levels — not from one limiting stage. Crucially, they show that CFFF is unresponsive to generic cognitive training yet shifts when subjects train with paradigms that engage the magnocellular-dorsal stream, what they call a defining feature of the boundary rather than a contradiction. The paper grounds this in three principles: a perceptual clock needs a stable reference frame, metabolic costs make faster processing prohibitive, and speed-accuracy trade-offs favor optimized integration windows. They stop short of claiming CFFF is a trait marker for cognition, instead framing links to working memory precision, metacognitive accuracy, and capacity limits as testable hypotheses. This falsifiable framework could help researchers distinguish genuinely plastic cognitive capacities from hard-wired sensory constraints.