Rhythmic visual stimulation enhances visual search via occipito-parietal alpha modulation: an electroencephalographic...

As a non-invasive neuromodulation technique, visual flicker entrainment has demonstrated considerable potential in enhancing basic visual perception; however, the neurophysiological mechanisms underlying these effects remain unclear. This study investigated whether rhythmic visual stimulation at individualized alpha frequencies can improve low-contrast visual search performance by selectively modulating alpha-band neural oscillations.

Forty-three healthy male participants completed a low-contrast visual search task under two conditions: personalized rhythmic flicker and arrhythmic (random) flicker. Behavioral performance was evaluated using reaction time, accuracy, and perceptual sensitivity. Simultaneously, high-density electroencephalographic data were recorded. Neural activity was quantified using power spectral density analysis across delta, theta, and beta frequency bands. Neural oscillatory characteristics were compared across prefrontal, central, parietal, and temporal areas under different flicker conditions.

Behaviorally, performance under the rhythmic flicker condition was significantly enhanced relative to that under the random flicker condition, as reflected by significantly reduced reaction times. Electrophysiologically, rhythmic flicker elicited a significant increase in overall alpha power (F _{(1, 42)} = 6.90, p = 0.012, η² _p = 0.14). Critically, this effect was region-specific: a significant Condition × Region interaction (F _{(3, 126)} = 7.83, p < 0.001). Alpha power in the occipital region was significantly higher during rhythmic flicker compared to arrhythmic flicker (mean difference = 0.51 μV², p = 0.007, uncorrected). The analysis of the parietal region using the Wilcoxon signed-rank test revealed a significant moderate increase (Z = 2.15, p = 0.031, uncorrected). No significant differences between conditions were found in the frontal or temporal regions (all p s > 0.05). Additionally, a significant Region × Electrode interaction was observed (F _{(6, 252)} = 12.83, p < 0.001, η² _p = 0.21). This indicates that the distribution of alpha power across electrodes differed by brain region. Furthermore, enhanced parietal alpha power was significantly correlated with a reduced reaction time (Pearson's r = -0.35, p = 0.021). By contrast, no significant modulation by rhythmic stimulation was observed in delta, theta, or beta bands (all Condition main effects and Condition × Region interactions, p > 0.05).

Individualized alpha-frequency visual flicker entrainment effectively enhances performance in male participants on complex visual search tasks, with the behavioral benefits mediated by selective modulation of neural oscillations in the parietal alpha band. These findings provide mechanistic electrophysiological evidence that rhythmic stimulation improves visual cognition by modulating frequency- and region-specific neural dynamics.