Department of Brain and Cognition, Leuven Brain Institute, KU Leuven, Leuven 3000, Belgium
Center for Developmental Psychiatry, Leuven Brain Institute, KU Leuven, Leuven 3000, Belgium.
J Neurosci. 2024 Apr 17;44(16):e1346232024. doi: 10.1523/JNEUROSCI.1346-23.2024.
Categorization is an essential cognitive and perceptual process, which happens spontaneously. However, earlier research often neglected the spontaneous nature of this process by mainly adopting explicit tasks in behavioral or neuroimaging paradigms. Here, we use frequency-tagging (FT) during electroencephalography (EEG) in 22 healthy human participants (both male and female) as a direct approach to pinpoint spontaneous visual categorical processing. Starting from schematic natural visual stimuli, we created morph sequences comprising 11 equal steps. Mirroring a behavioral categorical perception discrimination paradigm, we administered a FT-EEG oddball paradigm, assessing neural sensitivity for equally sized differences within and between stimulus categories. Likewise, mirroring a behavioral category classification paradigm, we administered a sweep FT-EEG oddball paradigm, sweeping from one end of the morph sequence to the other, thereby allowing us to objectively pinpoint the neural category boundary. We found that FT-EEG can implicitly measure categorical processing and discrimination. More specifically, we could derive an objective neural index of the required level to differentiate between the two categories, and this neural index showed the typical marker of categorical perception (i.e., stronger discrimination across as compared with within categories). The neural findings of the implicit paradigms were also validated using an explicit behavioral task. These results provide evidence that FT-EEG can be used as an objective tool to measure discrimination and categorization and that the human brain inherently and spontaneously (without any conscious or decisional processes) uses higher-level meaningful categorization information to interpret ambiguous (morph) shapes.
分类是一种重要的认知和感知过程，它是自发发生的。然而，早期的研究往往忽视了这个过程的自发性，主要通过在行为或神经影像学范式中采用显式任务来进行研究。在这里，我们使用脑电图（EEG）中的频率标记（FT）作为一种直接的方法，来精确定位自发的视觉分类处理。从示意性的自然视觉刺激开始，我们创建了包含 11 个相等步骤的形态序列。模仿行为分类感知辨别范式，我们进行了 FT-EEG 奇数范式的实验，评估了神经对刺激类别内和类别间相同大小差异的敏感性。同样，模仿行为类别分类范式，我们进行了扫频 FT-EEG 奇数范式的实验，从形态序列的一端扫到另一端，从而使我们能够客观地确定神经类别边界。我们发现 FT-EEG 可以隐式测量分类处理和辨别。更具体地说，我们可以从两个类别中区分出所需的神经指数，并且这个神经指数显示出了分类感知的典型标记（即，类别之间的辨别力比类别内更强）。隐式范式的神经发现也通过显式行为任务进行了验证。这些结果表明，FT-EEG 可作为一种客观工具，用于测量辨别和分类，并且大脑固有地且自发地（无需任何意识或决策过程）使用更高层次的有意义的分类信息来解释模糊（形态）形状。
