The Temporal Modulation Structure of Infant-Directed Speech

Abstract

The temporal modulation structure of adult-directed speech (ADS) is thought to be encoded by neuronal oscillations in the auditory cortex that fluctuate at different temporal rates. Oscillatory activity is thought to phase-align to amplitude modulations in speech at corresponding rates, thereby supporting parsing of the signal into linguistically relevant units. The temporal modulation structure of infant-directed speech (IDS) is unexplored. Here we compare the amplitude modulation (AM) structure of IDS recorded from mothers speaking, over three occasions, to their 7-, 9-, and 11-month-old infants, and the same mothers speaking ADS. Analysis of the modulation spectrum in each case revealed that modulation energy in the theta band was significantly greater in ADS than in IDS, whereas in the delta band, modulation energy was significantly greater for IDS than ADS. Furthermore, phase alignment between delta- and theta-band AMs was stronger in IDS compared to ADS. This remained the case when IDS and ADS were rate-normalized to control for differences in speech rate. These data indicate stronger rhythmic synchronization and acoustic temporal regularity in IDS compared to ADS, structural acoustic differences that may be important for early language learning.

The Temporal Statistics of Musical Rhythm across Western Genres: An Amplitude Modulation Phase Hierarchy Model

“…Table 1 provides a summary of these 4 temporal bands and the boundaries. It is important to note that, as shown in the spectral PCA, the results of the temporal PCA were highly similar to studies of CDS by Leong and Goswami [8] and to related studies of IDS [9]. Further, overall frequencies showed higher consistency across genres.…”

“…Indeed, speech-based modelling has revealed that IDS shows significant extra modulation energy in the delta band compared to adult-directed speech, contributing to its high rhythmicity [9]. The current data also map nicely to the Plomp and Levelt [55] modeling of the dissonance curve for spectral frequency (i.e., "pitch").…”

“…Recent evidence from adults suggests that these linguistic units can be identified from patterns of amplitude modulation (AM) in the acoustic sound waveforms of speech [7]. Meanwhile, related modelling of infant-and child-directed speech (IDS and CDS) has shown that the temporal patterning of prosodic, syllabic, rhyme and phoneme linguistic levels are yielded by the phase relations of temporal modulation bands in the amplitude envelope which correspond temporally to delta, theta and beta/gamma EEG bands, respectively [8,9]. An amplitude modulation phase hierarchy modelling approach has thus produced clear evidence regarding the acoustic foundations of the rhythm structure of IDS and CDS.…”

Neural encoding of the speech envelope by children with developmental dyslexia

“…Accurate perception of speech prosody is fundamental to the development of a mental lexicon of word forms in infancy and childhood, across languages (Jusczyk et al, 1999, Mehler et al, 1988). Further, recent analyses of the amplitude modulation structure of Australian English infant-directed speech (IDS) show a modulation peak at 2 Hz, the “prosodic rate” (see Leong, Kalashnikova, Burnham, & Goswami, 2014), not at 4–6 Hz, the modulation peak found for adult-directed speech (ADS, see Greenberg, Carvey, Hitchcock, & Chang, 2003). These different modulation peaks imply that early in development, accurate encoding of low frequency envelopes (delta band) could play a crucial role in setting up a phonological lexicon (Leong & Goswami, 2015).…”

Atypical right hemisphere response to slow temporal modulations in children with developmental dyslexia

“…The AM tiers were arranged hierarchically in the speech signal, with delta (2 Hz) as the master oscillator. Indeed, analyses of infant-directed speech (IDS) reveal that the greatest energy in the speech signal is in the delta band, suggestive of a core role for slow temporal modulations in initial language learning (Leong et al, 2014). The dominance of energy modulations in the delta band also provides an interesting contrast to adult-directed speech (ADS), in which theta band modulations dominate (~ 5 Hz).…”