Cortical Tracking of Sung Speech in Adults vs Infants: A Developmental Analysis

Abstract

Here we duplicate a neural tracking paradigm, previously published with infants (aged 4 to 11 months), with adult participants, in order to explore potential developmental similarities and differences in entrainment. Adults listened and watched passively as nursery rhymes were sung or chanted in infant-directed speech. Whole-head EEG (128 channels) was recorded, and cortical tracking of the sung speech in the delta (0.5–4 Hz), theta (4–8 Hz) and alpha (8–12 Hz) frequency bands was computed using linear decoders (multivariate Temporal Response Function models, mTRFs). Phase-amplitude coupling (PAC) was also computed to assess whether delta and theta phases temporally organize higher-frequency amplitudes for adults in the same pattern as found in the infant brain. Similar to previous infant participants, the adults showed significant cortical tracking of the sung speech in both delta and theta bands. However, the frequencies associated with peaks in stimulus-induced spectral power (PSD) in the two populations were different. PAC was also different in the adults compared to the infants. PAC was stronger for theta- versus delta- driven coupling in adults but was equal for delta- versus theta-driven coupling in infants. Adults also showed a stimulus-induced increase in low alpha power that was absent in infants. This may suggest adult recruitment of other cognitive processes, possibly related to comprehension or attention. The comparative data suggest that while infant and adult brains utilize essentially the same cortical mechanisms to track linguistic input, the operation of and interplay between these mechanisms may change with age and language experience.

Synchronizing with the rhythm: Infant neural entrainment to complex musical and speech stimuli

“…When comparing infants' neural entrainment with that of a small sample of adults using the identical experimental stimuli and analytic methods, we found very similar results in terms of SS-EP magnitudes and frequencies to which neural entrainment occurred, in line with recent neural tracking evidence revealing overall "more developmental similarities than developmental differences" between infants and adults in the entrainment to sung nursery rhymes (Attaheri et al, 2022b). For the African musical stimulus, we found robust neural entrainment for both infants and adults, although at different frequencies: whereas infants entrained at 3.48 Hz, corresponding to the faster perceived elements at the rhythmic level (i.e., the quaver, as shown in Figure 1A), adults entrained at 1.74 Hz, corresponding to the beat (i.e., a less perceptual and more «abstract» feature of the stimulus).…”

Emergence of the cortical encoding of phonetic features in the first year of life

“…The rhythmic cues and exaggerated stress patterns characterising nursery rhymes have been demonstrated to be important elements supporting speech perception and language learning 58,59 , accordingly they were ideal stimuli for the Cambridge UK BabyRhythm study. In prior TRF work, we have demonstrated similar envelope entrainment to these nursery rhymes by adults and infants 26 . Nevertheless, it is important to note that the regular rhythms and melodic properties of nursery rhymes makes the different from the typical speech TRF stimuli used with adults, such as audio-books and podcasts.…”

“…The results of this study add to the growing literature on cortical speech tracking 21,27,31,33,44,[60][61][62] . While the literature typically focuses on the cortical tracking of the speech envelope 16,24,[63][64][65][66] (including previous analyses of this dataset 21,26 ), the present investigation enriches our understanding of phonetic feature TRFs.…”

“…The results of this study add to the growing literature on cortical speech tracking 21,27,31,33,44,60–62 . While the literature typically focuses on the cortical tracking of the speech envelope 16,24,63–66 (including previous analyses of this dataset 21,26 ), the present investigation enriches our understanding of phonetic feature TRFs. Prior TRF studies of phonetic encoding in adults and children have revealed that phonetic processing is affected by speech clarity 43 , selective attention 29 , and proficiency in a second language 33 , and shows correlations with psychometric measures of phonemic awareness 32 .…”

“…Neural tracking of the speech envelope (or envelope tracking) was shown to reflect both bottomup and top-down cortical processes in adult listeners, encompassing fundamental functions such as selective attention [15][16][17] , working memory processing load 18 , and prediction 19,20 . While robust envelope tracking has also been demonstrated in infants [21][22][23][24][25][26] , envelope measures only reveal some of the cortical mechanisms underlying speech perception. Recent work with adults and children has demonstrated that TRFs can be extended to isolate the neural encoding of targeted speech properties of interest, starting from phonetic features 27 .…”