Infant Directed Speech Enhances Statistical Learning in Newborn Infants: An ERP Study

Abstract

Statistical learning and the social contexts of language addressed to infants are hypothesized to play important roles in early language development. Previous behavioral work has found that the exaggerated prosodic contours of infant-directed speech (IDS) facilitate statistical learning in 8-month-old infants. Here we examined the neural processes involved in on-line statistical learning and investigated whether the use of IDS facilitates statistical learning in sleeping newborns. Event-related potentials (ERPs) were recorded while newborns were exposed to12 pseudo-words, six spoken with exaggerated pitch contours of IDS and six spoken without exaggerated pitch contours (ADS) in ten alternating blocks. We examined whether ERP amplitudes for syllable position within a pseudo-word (word-initial vs. word-medial vs. word-final, indicating statistical word learning) and speech register (ADS vs. IDS) would interact. The ADS and IDS registers elicited similar ERP patterns for syllable position in an early 0-100 ms component but elicited different ERP effects in both the polarity and topographical distribution at 200-400 ms and 450-650 ms. These results provide the first evidence that the exaggerated pitch contours of IDS result in differences in brain activity linked to on-line statistical learning in sleeping newborns.

Fig 1. Example F0 contours, spectrograms of syllables, and schematic of the experimental procedure.

Top panel. Example F0 contours and spectrograms of syllables presented in the ADS (left) and IDS (right) registers. Bottom panel. Schematic of the experimental procedure, i.e., 4 pseudo-words from the speech stream.

Fig 2. Grand-averaged ERPs for word-initial, word-medial, and word-final syllables for ADS and IDS registers collapsed across the 10 exposure blocks.

Grand-averaged ERPs to the word-initial (black line), word-medial (light gray), and word-final (dashed line) syllables in the tri-syllabic pseudo-words for the ADS (top panel) and IDS (right panel) registers collapsed across the 10 exposure blocks. Infants heard each syllable 111 times. Enlarged area displays results at represented electrode sites for each measurement window. Grey bars denote significant differences in mean amplitudes between syllable positions. Negative voltages (microvolts) are plotted upward.

Fig 3. Mean amplitude for the ADS and IDS registers in the 0–100 ms, 200–400 ms and 450–650 ms measurement windows.

Mean amplitude (in microvolts) for the ADS and IDS registers in the 0–100 ms (left panel), 200–400 ms (middle panel) and 450–650 ms (right panel) measurement windows averaged across the 10 exposure blocks, 3 syllable positions and 6 electrode sites. Asterisks indicate significant differences.