Local temporal regularities in child-directed speech in Spanish

Purpose: 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: 18 female adults addressed their 4-year-old children versus other adults spontaneously and also read aloud (CDS versus ADS). We compared CDS and ADS speech productions using a spectro-temporal model (S-AMPH, Leong & Goswami, 2015), obtaining three temporal metrics: 1) distribution of modulation energy, 2) temporal regularity of stressed syllables, and 3) syllable rate. Results: CDS was characterized by 1) significantly greater modulation energy in the lower frequencies (0.5-4 Hz), 2) more regular rhythmic occurrence of stressed syllables, and 3) 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.