Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, 6525 HR Nijmegen, The Netherlands.
J Neurosci. 2013 Feb 13;33(7):3212-20. doi: 10.1523/JNEUROSCI.3755-12.2013.
Several studies have demonstrated that prestimulus occipital alpha-band activity substantially influences subjective perception and discrimination of near-threshold or masked visual stimuli. Here, we studied the role of prestimulus power fluctuations in two visual phenomena called double-flash illusion (DFI) and fusion effect (FE), both consisting of suprathreshold stimuli. In both phenomena, human subjects' perception varies on a trial-by-trial basis between perceiving one or two visual stimuli, despite constant stimulation. In the FE, two stimuli correspond to veridical perception. In the DFI, two stimuli correspond to an illusory perception. This provides for a critical test of whether reduced alpha power indeed promotes veridical perception in general. We find that in both, DFI and FE, reduced prestimulus occipital alpha predicts the perception of two stimuli, regardless of whether this is veridical (FE) or illusory (DFI). Our results suggest that reduced alpha-band power does not always predict improved visual processing, but rather enhanced excitability. In addition, for the DFI, enhanced prestimulus occipital gamma-band power predicted the perception of two visual stimuli. These findings provide new insights into the role of prestimulus rhythmic activity for visual processing.
已有多项研究表明，刺激前枕叶 alpha 频段活动会显著影响对近阈或掩蔽视觉刺激的主观感知和辨别。在此，我们研究了刺激前功率波动在两种视觉现象中的作用，这两种现象都包含阈上刺激：双闪光错觉（DFI）和融合效应（FE）。在这两种现象中，尽管刺激是恒定的，人类受试者在每次试验中对感知一个或两个视觉刺激的感知会有所不同。在 FE 中，两个刺激对应于真实的感知。在 DFI 中，两个刺激对应于错觉感知。这为减少 alpha 功率是否确实普遍促进真实感知提供了一个关键的测试。我们发现，在 DFI 和 FE 中，减少刺激前枕叶 alpha 功率可预测感知两个刺激，无论这是真实的（FE）还是错觉的（DFI）。我们的结果表明，减少 alpha 频段功率并不总是预测改善视觉处理，而是增强兴奋性。此外，对于 DFI，增强的刺激前枕叶伽马频段功率可预测感知两个视觉刺激。这些发现为视觉处理中刺激前节律活动的作用提供了新的见解。
