Search Abstracts | Symposia | Slide Sessions | Poster Sessions
Newly acquired knowledge of word meanings enhances neural entrainment to speech
Poster Session B, Wednesday, September 30, 4:30 - 6:30 pm, Wangari Maathai
Albert E. Kim1, Jacqui Fallon1, John Trueswell2; 1University of Colorado, Boulder, 2University of Pennsylvania
A central goal for neurophysiological studies of language learning is to identify measures that reveal whether, and when, novel linguistic input has begun to carry meaning for the learner. Neural entrainment to continuous speech is a promising candidate measure because brain activity temporally aligns with low-frequency rhythmic structure in the speech signal, and this alignment is often enhanced by increased speech intelligibility. However, whether intelligibility effects on entrainment reflect access to linguistic meaning, rather than lower-level acoustic processing, remains contested. Typical manipulations of intelligibility, such as noise vocoding, alter both semantic accessibility and acoustic structure, leaving open the possibility that acoustic features alone drive intelligibility effects. Although intelligibility of degraded speech can be increased by providing listeners prior linguistic knowledge without affecting acoustic content, this does not enhance entrainment, suggesting it reflects only low-level processing. We tested the hypothesis that newly acquired knowledge about word meanings would enhance EEG-speech entrainment in an experiment that manipulated such knowledge while holding the acoustic signal constant and avoiding acoustic degradation. Participants listened, task-free, to a 9-minute pseudoword story twice, before and after a training session in which they were taught the meanings of 10 pseudowords and simply familiarized with the forms of 10 others. The assignment of pseudowords to the meaning-taught and familiarized conditions was counterbalanced across participants. We quantified entrainment as phase coherence (PC) between EEG and speech in 1000 ms epochs timelocked to the pseudoword onsets. The speech amplitude envelope and EEG signals were bandpass filtered 4–8 Hz, instantaneous phase was estimated via the Hilbert transform, and trial level PC was calculated as the magnitude of the mean of all unit complex vectors at angles determined by the two signals’ phase differences. PC was averaged for analysis within bilateral temporal ROIs (left: C1/3/5, CP1/3/5; right: C2/4/6, CP2/4/6). Preliminary results (N=19; planned N=30) suggest that PC was greater during the second than the first encounter with pseudowords, consistent with learning, specifically for meaning-taught words and specifically in the left ROI (learning phase×hemisphere×wordtype interaction in a within subjects ANOVA was F(1,18)=4.27, p=.054). A focused test in the left ROI of the learning phase×word type interaction was also marginal (F(1,18)=4.33, p=.052). PC scores in the left ROI did not differ for meaning-taught and familiarized pseudowords before training (t(18)=−0.09, p=.537) but were marginally different after training (t(18)=1.68, p=0.056). The right ROI showed no learning-related interaction (F(1,18) = 0.16, p = .693). These preliminary results are consistent with our hypothesis that semantic access modulates neural entrainment to speech. Acquiring form-to-meaning mappings appears to enhance neural entrainment, specifically at left temporal sites. This effect cannot be attributed to acoustic differences because pre and post learning stimuli were acoustically identical within participants. Data collection and alternative approaches to quantifying entrainment (cross-spectral density, temporal response functions) are ongoing. If entrainment is increased by access to meaning, it could provide unique, task-free sensitivity to semantic access during continuous speech listening and language learning.
Topic Areas: Speech Perception, Language Development/Acquisition