Fine-tuning of utterance length to preverbal infants: effects on later language development.

The purpose of this study was to determine (1) whether mothers simplify their speech during the second half of the first year of development when infants begin to comprehend words and use gestures to communicate intentionally, and (2) whether individual differences in mothers' speech adjustments influence their infants' later language acquisition. The subjects for the study were 14 mother-infant pairs from a medically low risk sample who were followed longitudinally. Mothers' mean length of utterance (MLU) was calculated from transcripts of face-to-face interaction when the infants were 0:3, 0:6, and 0:9 in age. Mothers who provided responsive and stimulating environments, as indicated by HOME scores, also reduced their MLU over the age range studied. Moreover, mothers' MLU adjustments during the first year were more predictive than the HOME scale in forecasting receptive language development at 1:6. In contrast, expressive language abilities at 1:6 were unrelated to the environmental variables measured but were predicted by child characteristics such as the infant's sex. These results suggest that a mother's ability to 'fine-tune' her early linguistic input may be predictive of her child's later receptive language functioning. Precursors of fine-tuning, such as maternal beliefs in reciprocity and infant object orientation, are discussed.