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Prosodic structure aids neural tracking of speech in the delta band
Poster Session F, Friday, October 2, 2:45 - 4:45 pm, Wangari Maathai
Mathias Scharinger1,2,3, Christiane Eichenauer3, Ulrike Domahs1,2,3; 1Institute of German Linguistics, University of Marburg, Germany, 2Center for Mind, Brain & Behavior, Universities of Marburg & Gießen, Germany, 3Research Unit »Weak Elements in Phonology«, University of Marburg, Germany
Neural tracking of speech is based on the coherence of cortical oscillations and speech acoustic information. In previous studies, cortical oscillations in the range of the theta frequency (4–8 Hz) have been discussed as a mechanism to segment the continuous speech signal into syllable-sized units, thereby supporting speech processing. Within linguistic research, the syllable is just one unit in the prosodic hierarchy. Combinations of strong and weak syllables into feet provide the prosodic scaffolding of speech, with a particular preference in German for the trochaic strong–weak pattern. While brain oscillations have been shown to align to syllable structure, it is less clear whether they align to supra-syllabic foot structure in a similar way, however. We hypothesize that a candidate oscillation for parsing foot structure occurs in the delta band (1-3 Hz). To probe this assumption, we modified the Sternberg memory task using 8-digit numbers that were arranged in either trochaic (i.e., strong–weak, “dréi – vier” [thrée – four]) or iambic foot structure (i.e., weak–strong, “drei – víer” [three – fóur]). A total of 25 participants listened to these 8-digit sequences and had to memorize the numbers. A visual 4-digit probe number was used to test recall performance. The probe was either congruent or incongruent with the foot structure of the 8-digit numbers. Recall performance was measured by accuracy and reaction times. Additionally, we recorded the continuous EEG from 32 active scalp electrodes. Accuracy was significantly better for probes congruent with the foot structure, evidencing that feet are indeed used during the encoding of speech. Reaction times for correct recall were faster for probes with congruent foot structure and in general, for the trochaic as compared to iambic foot structure of the numbers. Neural tracking was assessed by power- and phase coherence measures within the theta and the delta frequency band, calculated on epochs ranging from 0.5 s before and 4 s after the acoustically presented number sequences. Notably, power coherence was stronger within delta than within theta frequency, and for trochaic as compared to iambic foot structure. Differences between coherence in the delta- and theta band were reduced for trochaic foot structure, as evidenced by a significant foot x frequency band interaction. Furthermore, phase coherence was stronger in the delta than in the theta band, and for the trochaic compared to the iambic foot structure. The foot x frequency band interaction was driven by the effect in the delta band, with notably stronger coherence for trochaic than for iambic foot structure. Together, these findings provide evidence for the role of foot structure during speech comprehension in a memory task, highlighting the functional relevance of delta oscillations for prosodic processing. The pattern of results also demonstrates the special status of the trochaic foot for speech processing in German. As neural oscillations have been shown to interact with attention and prediction, future research should clarify whether the neural tracking of foot structure within the delta band corresponds to the optimal alignment of attention to prosodically prominent positions within the continuous speech signal.
Topic Areas: Prosody, Speech Perception