Temporal regularities in child-directed speech (Pérez-Navarro et al., 2022)

Purpose: The purpose of this study is to characterize the local (utterance-level) temporal regularities of child-directed speech (CDS) that might facilitate phonological development in Spanish, classically termed a syllable-timed language.

Method: Eighteen female adults addressed their 4-year-old children versus other adults spontaneously and also read aloud (CDS vs. adult-directed speech [ADS]). We compared CDS and ADS speech productions using a spectrotemporal model (Leong & Goswami, 2015), obtaining three temporal metrics: (a) distribution of modulation energy, (b) temporal regularity of stressed syllables, and (c) syllable rate.

Results: CDS was characterized by (a) significantly greater modulation energy in the lower frequencies (0.5–4 Hz), (b) more regular rhythmic occurrence of stressed syllables, and (c) a slower syllable rate than ADS, across both spontaneous and read conditions.

Discussion: CDS is characterized by a robust local temporal organization (i.e., within utterances) with amplitude modulation bands aligning with delta and theta electrophysiological frequency bands, respectively, showing greater phase synchronization than in ADS, facilitating parsing of stress units and syllables. These temporal regularities, together with the slower rate of production of CDS, might support the automatic extraction of phonological units in speech and hence support the phonological development of children.

Supplemental Material S1. Formula of cross-frequency phase synchronization index (PSI).

Supplemental Material S2. Delta-theta PSI values across different n:m ratios. The point within each distribution represents the mean, and the bars represent standard deviations.

Supplemental Material S3. Pearson correlation between manual and automatic syllable rate computation. Correlation index at the top left corner.

Supplemental Material S4. Delta-theta PSI across speaking conditions and spectral bands. Error bars represent standard error of the mean. Pie plot in the bottom right corner represents the percentage of Tukey HSD contrasts for which PSI is higher for CDS (orange), ADS (blue), or resulted in a non-significant difference (gray, adjusted p-threshold = .05).

Pérez-Navarro, J., Lallier, M., Clark, C., Flanagan, S., & Goswami, U. (2022). Local temporal regularities in child-directed speech in Spanish. Journal of Speech, Language, and Hearing Research. Advance online publication. https://doi.org/10.1044/2022_JSLHR-22-00111