Ladouce Simon, Dehais Frédéric
Human Factors and Neuroergonomics, Institut Superieur de l'Aeronautique et de l'Espace, Toulouse, France.
Brain and Cognition & Leuven Brain Institute, KU Leuven, Leuven, Belgium.
Imaging Neurosci (Camb). 2024 Jul 12;2. doi: 10.1162/imag_a_00223. eCollection 2024.
Steady-State Visually Evoked Potentials (SSVEPs) manifest as a sustained rhythmic activity that can be observed in surface electroencephalography (EEG) in response to periodic visual stimuli, commonly referred to as flickers. SSVEPs are widely used in fundamental cognitive neuroscience paradigms and Brain-Computer Interfaces (BCI) due to their robust and rapid onset. However, they have drawbacks related to the intrusive saliency of flickering visual stimuli, which may induce eye strain, cognitive fatigue, and biases in visual exploration. Previous findings highlighted the potential of altering features of flicker stimuli to improve user experience. In this study, we propose to reduce the amplitude modulation depth of flickering stimuli down to the individuals' perceptual visibility threshold (periliminal) and below (subliminal). The stimulus amplitude modulation depth represents the contrast difference between the two alternating states of a flicker. A simple visual attention task where participants responded to the presentation of spatially cued target stimuli (left and right) was used to assess the validity of such periliminal and subliminal frequency-tagging probes to capture spatial attention. The left and right sides of the screen, where target stimuli were presented, were covered by large flickers (13 and 15 Hz, respectively). The amplitude modulation depth of these flickers was manipulated across three conditions: control, periliminal, and subliminal. The latter two levels of flickers amplitude modulation depth were defined through a perceptual visibility threshold protocol on a single-subject basis. Subjective feedback indicated that the use of periliminal and subliminal flickers substantially improved user experience. The present study demonstrates that periliminal and subliminal flickers evoked SSVEP responses that can be used to derive spatial attention in frequency-tagging paradigms. The single-trial classification of attended space (left versus right) based on SSVEP response reached an average accuracy of 81.1% for the periliminal and 58% for the subliminal conditions. These findings reveal the promises held by the application of inconspicuous flickers to both cognitive neuroscience research and BCI development.
稳态视觉诱发电位（SSVEPs）表现为一种持续的节律性活动，可在表面脑电图（EEG）中观察到，它是对周期性视觉刺激（通常称为闪烁）的响应。由于其稳健且快速出现，SSVEPs在基础认知神经科学范式和脑机接口（BCI）中被广泛应用。然而，它们存在与闪烁视觉刺激的显著侵入性相关的缺点，这可能会导致眼睛疲劳、认知疲劳以及视觉探索中的偏差。先前的研究结果强调了改变闪烁刺激特征以改善用户体验的潜力。在本研究中，我们建议将闪烁刺激的幅度调制深度降低到个体的感知可见阈值（阈限下）及以下（阈下）。刺激幅度调制深度表示闪烁的两个交替状态之间的对比度差异。使用一个简单的视觉注意力任务，即参与者对空间提示的目标刺激（左和右）的呈现做出反应，来评估这种阈限下和阈下频率标记探针捕捉空间注意力的有效性。呈现目标刺激的屏幕左右两侧被大的闪烁（分别为13和15赫兹）覆盖。这些闪烁的幅度调制深度在三种条件下进行操纵：对照、阈限下和阈下。后两个闪烁幅度调制深度水平是通过基于单受试者的感知可见阈值协议定义的。主观反馈表明，使用阈限下和阈下闪烁显著改善了用户体验。本研究表明，阈限下和阈下闪烁诱发的SSVEP反应可用于在频率标记范式中推导空间注意力。基于SSVEP反应对关注空间（左对右）的单次试验分类在阈限下条件下平均准确率达到81.1%，在阈下条件下为58%。这些发现揭示了将不显眼的闪烁应用于认知神经科学研究和BCI开发所带来的前景。
