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Implicit, automatic semantic word categorisation as revealed by fast periodic visual stimulation

Poster B66 in Poster Session B and Reception, Thursday, October 6, 6:30 - 8:30 pm EDT, Millennium Hall

Angelique Volfart^1,2,3, Grace E. Rice⁴, Matthew A. Lambon Ralph⁴, Bruno Rossion^2,3,5; ¹Queensland University of Technology, ²University of Louvain, ³CRAN, University of Lorraine, ⁴MRC Cognition and Brain Sciences Unit, ⁵CHRU-Nancy, University of Lorraine

Conceptual knowledge allows the categorisation of items according to their meaning beyond their physical similarities. This ability to respond to different stimuli (e.g., a leek, a cabbage, etc.) based on similar semantic representations (e.g., all vegetables) is particularly important for language processing, because word meaning and the stimulus form are unrelated. The neural basis of this core human ability is debated and is complicated by the strong reliance of most neural measures on explicit tasks, involving many non-semantic processes. Here we establish an implicit method, i.e., fast periodic visual stimulation (FPVS) coupled with electroencephalography (EEG), to study conceptual categorisation processes with written word stimuli. In a first experiment, fourteen neurotypical participants were presented with different written words belonging to the same semantic category (e.g., different animals) alternating at 4Hz rate. Words from a different semantic category (e.g., different cities) appeared every 4 stimuli (i.e., at 1Hz). Following a few minutes of recording, objective electrophysiological responses at 1Hz, highlighting the human brain’s ability to implicitly categorize stimuli belonging to distinct conceptual categories, were found over the left occipito-temporal region. Topographic differences were observed depending on whether the periodic change involved living items, associated with relatively more ventro-temporal activity as compared to non-living items associated with relatively more dorsal posterior activity (Volfart et al., 2021). In a second, control experiment, we addressed whether the periodic EEG responses could be (partly) generated simply from the rare presentation of specific stimuli as oddball among more frequently presented stimuli, irrespective of their semantic categories, (i.e., a statistical learning effect; De Rosa et al., 2022). We tested seventeen neurotypical participants with the condition providing the largest amplitudes in the first experiment (cities/animals), manipulating the number of base/alternate stimuli (either 8 base and 8 alternate stimuli [8x8] or 24 base and alternate stimuli [24x24]) and the conceptual category consistency (with [CC] or without [NCC], e.g., in the 24x24 NCC condition, base stimuli were words of 12 animals and 12 cities, and alternate stimuli were different words of 12 animals and 12 cities). With 8 stimuli, we found significant left occipito-temporal 1Hz responses even in the NCC condition, reflecting a statistical learning effect. While a significantly larger number of significant electrodes were found in the CC condition, there was no overall amplitude difference between CC and NCC conditions over the key brain region. However, critically, with 24 stimuli, there was no significant occipito-temporal 1Hz response in the NCC condition anymore, while the response even increased for the CC condition. These observations indicate that statistical learning effects alone can elicit spurious EEG responses at 1Hz in paradigms with small stimulus sets, but they are not as robust as conceptual category effects and disappear when larger stimulus sets are used. Overall, this study demonstrates the validity and high sensitivity of an implicit frequency-tagged marker of word-based semantic memory abilities.

Topic Areas: Meaning: Lexical Semantics, Methods