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Neural Speech Processing Under Selective Attention: Isolating the Effects of Speech Understanding and Familiarity
Poster Session D, Thursday, October 1, 4:30 - 6:30 pm, Wangari Maathai
Jessie Rademacher1,2, Marc Schönwiesner1; 1Leipzig University, 2International Max Planck Research School on Cognitive NeuroImaging
Introduction: Selective auditory attention enables listeners to focus on relevant speech while suppressing distractions. Comprehensible background speech is particularly disruptive, yet it remains unclear whether unattended speech is semantically processed or whether interference is primarily driven by speech content or familiarity with speech sounds. A major challenge in previous research has been the comparability of comprehensible and incomprehensible speech stimuli, as manipulations such as vocoding or inversion alter acoustic properties and naturalness. Likewise, comparing native and foreign languages introduces linguistic and acoustic differences unrelated to comprehension. To address these limitations, we developed a paradigm that isolates comprehensibility while keeping the acoustic stimulus constant. Using identical speech material before and after participants learned a micro-language, we investigated how comprehension shapes neural processing of attended and unattended speech. Methods: Healthy participants completed an auditory selective-attention task with continuous target and distractor speech during electroencephalography (EEG) and pupillometry recordings. Distractor speech consisted of a micro-language that was initially incomprehensible. Participants performed the task before and after one week of language training, after which they achieved fluent comprehension of the distractor speech. A control group received equivalent exposure to the speech material without learning word meanings, controlling for familiarity effects. Neural responses were analyzed using multivariate temporal response function methods. Results: We show that neural tracking of the distractor speech differed before and after language learning, with reduced neural encoding for comprehensible distractor speech around 170ms. Notably, for unattended speech, similar effects were also observed in the exposure group, suggesting that familiarity with speech sounds alone modulates neural encoding. In contrast, when distractor speech was attended, differences emerged mainly in the language-learning group, indicating a stronger contribution of semantic comprehension. In addition, pupil size varied between comprehension and non-comprehension conditions, consistent with changes in arousal or listening effort associated with meaningful distractor speech. Conclusion: By clearly isolating speech comprehension and acoustic familiarity, this paradigm provides a controlled approach for examining the neural mechanisms of selective auditory attention. The findings suggest that familiarity and semantic comprehension contribute differently depending on attentional state: familiarity appears sufficient to influence unattended speech processing, whereas semantic understanding exerts stronger effects when speech is actively attended. These results highlight the importance of separating acoustic familiarity from linguistic comprehension in studies of speech distraction and provide evidence that comprehension-related changes in neural speech encoding can be detected even when the acoustic input remains identical.
Topic Areas: Control, Selection, and Executive Processes,