Gulbinaite Rasa, İlhan Barkın, VanRullen Rufin
Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5549, Faculté de Médecine Purpan, Toulouse, 31000 France,
Université de Toulouse, Centre de Recherche Cerveau et Cognition, Université Paul Sabatier, Toulouse, 31052 France, and.
J Neurosci. 2017 Jul 26;37(30):7219-7230. doi: 10.1523/JNEUROSCI.3929-16.2017. Epub 2017 Jun 29.
The modulatory role of spontaneous brain oscillations on perception of threshold-level stimuli is well established. Here, we provide evidence that alpha-band (∼10 Hz) oscillations not only modulate perception of threshold-level sensory inputs but also can drive perception and generate percepts without a physical stimulus being present. We used the "triple-flash" illusion: Occasional perception of three flashes when only two spatially coincident veridical ones, separated by ∼100 ms, are presented. The illusion was proposed to result from superposition of two hypothetical oscillatory impulse response functions generated in response to each flash: When the delay between flashes matches the period of the oscillation, the superposition enhances a later part of the oscillation that is normally damped; when this enhancement crosses perceptual threshold, a third flash is erroneously perceived (Bowen, 1989). In Experiment 1, we varied stimulus onset asynchrony and validated Bowen's theory: The optimal stimulus onset asynchrony for illusion to occur was correlated, across human subjects (both genders), with the subject-specific impulse response function period determined from a separate EEG experiment. Experiment 2 revealed that prestimulus parietal, but no occipital, alpha EEG phase and power, as well as poststimulus alpha phase-locking, together determine the occurrence of the illusion on a trial-by-trial basis. Thus, oscillatory reverberations create something out of nothing: A third flash where there are only two. We highlight a novel property of alpha-band (∼10 Hz) oscillations based on three experiments (two EEG and one psychophysics) by demonstrating that alpha-band oscillations do not merely modulate perception, but can also drive perception. We show that human participants report seeing a third flash when only two are presented (the "triple-flash" illusion) most often when the interflash delay matches the period of participant's oscillatory impulse response function reverberating in alpha. Within-subject, the phase and power of ongoing parietal, but not occipital, alpha-band oscillations at the time of the first flash determine illusory percept on a trial-by-trial basis. We revealed a physiologically plausible mechanism that validates and extends the original theoretical account of the triple-flash illusion proposed by Bowen in 1989.
大脑自发振荡对阈限水平刺激感知的调节作用已得到充分证实。在此，我们提供证据表明，阿尔法波段（约10赫兹）振荡不仅能调节阈限水平感觉输入的感知，还能在没有物理刺激的情况下驱动感知并产生知觉。我们使用了“三闪光”错觉：当仅呈现两个空间重合、间隔约100毫秒的真实闪光时，偶尔会感知到三次闪光。该错觉被认为是由对每次闪光产生的两个假设振荡脉冲响应函数叠加所致：当闪光之间的延迟与振荡周期匹配时，叠加会增强振荡中通常会衰减的后期部分；当这种增强超过感知阈限时，就会错误地感知到第三次闪光（鲍恩，1989年）。在实验1中，我们改变了刺激起始异步性并验证了鲍恩的理论：在人类受试者（男女皆有）中，错觉发生的最佳刺激起始异步性与通过单独的脑电图实验确定的受试者特异性脉冲响应函数周期相关。实验2表明，刺激前顶叶而非枕叶的阿尔法脑电图相位和功率，以及刺激后阿尔法相位锁定，共同在逐个试次的基础上决定错觉的发生。因此，振荡回响能凭空创造出东西：只有两次闪光时却出现了第三次闪光。基于三项实验（两项脑电图实验和一项心理物理学实验），我们突出了阿尔法波段（约10赫兹）振荡的一个新特性，即表明阿尔法波段振荡不仅能调节感知，还能驱动感知。我们表明，当只呈现两次闪光（“三闪光”错觉）时，人类参与者最常报告看到第三次闪光的情况是，闪光间隔与参与者在阿尔法波段中回响的振荡脉冲响应函数周期相匹配。在个体内部，第一次闪光时正在进行的顶叶而非枕叶阿尔法波段振荡的相位和功率在逐个试次的基础上决定错觉知觉。我们揭示了一种生理上合理的机制，该机制验证并扩展了鲍恩在1989年提出的关于三闪光错觉的原始理论解释。
