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Luhe Li, Yuko Yotsumoto; Neural entrainment influences visual perception without the conscious perception of stimulus changes. Journal of Vision 2020;20(11):487. doi: https://doi.org/10.1167/jov.20.11.487.
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Rhythmic visual stimulation can cause neural entrainment, the synchronization of intrinsic oscillations and the external stimulus rhythms. Neural entrainment has been reported to modulate perceptual processes, such as enhancing perceived brightness and facilitating temporal prediction. However, flicker-induced neural entrainment effect is confounded by change saliency, the subjective perception of stimulus changes. It remains unclear whether neural entrainment without change saliency could influence visual perception. To preclude change saliency, we used frequencies higher than the critical fusion threshold to render flicker perception stable. Importantly, we simultaneously presented two flickers at 55.5 Hz and 62.5 Hz while measuring electroencephalography to assess whether their beat frequency (i.e., 7 Hz) arose by the nonlinear processing at the visual cortex. To test the influence of neural entrainment at the beat, we used this combined flicker in a duration discrimination task with a two-alternative forced-choice design. In this task, 17 participants compared seven durations of the combined flicker with the standard duration of a stable stimulus. Behavioral results revealed that the combined flicker induced time dilation, supporting the engagement of neural entrainment. We also conducted the power analysis, inter-trial coherence analysis, and rhythmic entrainment source separation that could increase the signal-to-noise (SNR) ratio of SSVEPs. The SNR at the lower fundamental frequency was significantly larger than the control condition, suggesting that the neural entrainment of fundamental frequencies was successful. We concluded that neural entrainment could influence visual perception without the conscious perception of stimulus changes, while stronger neural entrainment methods are needed to further examine the existence of the beat derived from high frequencies.
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