No abstract

Despite good early rhythm processing abilities, and clear enjoyment of music, infants appear not to be able to spontaneously synchronize their movement to the beat of a song (Zentner and Eerola, Proceedings of the National Academy of Sciences, 107, 2010, 5768). We present a new social bell‐ringing task designed to facilitate synchronous movement to music in infants. Ten‐month‐olds, 18‐month‐olds, and adults were played musical tracks of various tempos and given handheld bells to ring, in the presence of either a live experimenter or an animated nonsocial stimulus. Surface electromyography (EMG) was used to measure the timing of arm movements during periods of bell ringing. Infants showed no evidence of synchronous bell ringing at any tempo. However, while the 10‐month‐olds did not modulate their ringing to the music tempo, the 18‐month‐olds showed tempo‐flexibility. Moreover, 18‐month‐olds displayed more associated behaviors such as bouncing and rocking in the absence (rather than presence) of a social partner, whereas the behavior of the 10‐month‐olds was not modulated by the presence or absence of a social partner. The results suggest a distinction between “moving together” and “moving to the beat,” which may have separate underlying mechanisms and developmental trajectories.

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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.

Time is central to any understanding of the world. In adults, estimation errors grow linearly with the length of the interval, much faster than would be expected of a clock-like mechanism. Here we present the first direct demonstration that this is also true in human infants. Using an eye-tracking paradigm, we examined 4-, 6-, 10-, and 14-month-olds’ responses to the omission of a recurring target, on either a 3- or 5-s cycle. At all ages (a) both fixation and pupil dilation measures were time locked to the periodicity of the test interval, and (b) estimation errors grew linearly with the length of the interval, suggesting that trademark interval timing is in place from 4 months.

The foundations for language acquisition are laid in infancy. A key feature of infant-directed speech (IDS) is that the slowest modulations of its amplitude envelope (~2 Hz) contain more energy than in adult-directed speech. These slow modulations may provide a cross-language rhythmic scaffold for the neural tracking of speech in infancy. To investigate relations between early neural processing of speech and language acquisition in English, the BabyRhythm project followed 113 infants during infancy and toddlerhood. The neural predictor of language development reported here was the cortical tracking of slow, rhythmic audiovisual stimuli, processing of which is known to differ in older children with dyslexia. To find out how such stimuli are tracked early in development, infants were presented with videos of a woman repeating the syllable “Ta” twice per second, and a ball bouncing on a drum to create a 2Hz beat. At the ages of six and nine months, infants exhibited a significant peak in EEG power at 2Hz when listening to these stimuli, indicating that the infant brain was responding to these stimuli at the expected frequency. Time-frequency analysis showed increased inter-trial EEG phase coherence at 2Hz, suggesting that the increase in oscillatory power was driven by the stimuli. There were no differences in how the speech and non-speech stimuli were tracked. These results indicate that the infant brain can track the rhythm of slow auditory stimuli. They lay the foundation for future investigation of how individual differences in tracking might relate to later language acquisition.

Brain activity is known to track the amplitude envelope of adult-directed speech (ADS). Infant-directed speech (IDS) has significantly greater modulation energy than ADS in an amplitude-modulation (AM) band centered on ~2 Hz. Accordingly, cortical tracking of speech by delta-band neural signals may be critical for language acquisition. We examined the presence and maturation of low frequency (<12Hz) cortical speech tracking, recording EEG longitudinally from 60 infants aged 4-, 7-, and 11- months listening to sung nursery rhymes. After establishing stimulus-induced neural signals in delta and theta, cortical tracking at each age was assessed in the delta, theta and alpha [control] bands using a multivariate temporal response function (mTRF) method. Delta-beta, delta-gamma, theta-beta and theta-gamma phase-amplitude coupling (PAC) was also assessed. Significant delta and theta but not alpha tracking was found, the earliest such demonstration for speech. Significant PAC was present at all ages, with stronger delta-driven coupling observed, as hypothesised.

Highlights EEG was recorded while 8-week old infants listened to rhythmic speech and non-speech. Both A CNN and SVM reliably classified infant brain responses. The CNN was more robust to noisy EEG data. Simple rhythmic EEG measures may enable prediction of language outcomes.