Input and processing factors affecting infants' vocabulary size at 19 and 25 months

Jae Yung Song*, Katherine Demuth, James Morgan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)
16 Downloads (Pure)


This study examined the relative contributions of three factors to individual differences in vocabulary development: the acoustic quality of mothers' speech, the quantity of mothers' speech, and infants' ability to recognize words. To examine the quality and quantity of mothers' speech, recordings were collected from 48 mothers when their infants were 17 months old. Infants' ability to recognize words was gauged by their performance in a perception experiment at 19 months. We examined the relationship between these measures and infants' vocabulary size at 19 and 25 months. The quantity of mothers' speech accounted for the greatest amount of variance in infants' vocabulary size at 19 months; infants' ability to recognize words followed next. At 25 months, when mothers' speech alone is presumably no longer the primary input for infants, infants' ability to recognize words at 19 months was a better predictor of vocabulary size. The acoustic quality of mothers' speech was not correlated with infants' vocabulary size at either age. The findings highlight the importance of considering multiple factors that contribute to early word learning, providing a better understanding of the mechanisms underlying the facilitation process.

Original languageEnglish
Article number2398
Pages (from-to)1-11
Number of pages11
JournalFrontiers in Psychology
Issue numberNOV
Publication statusPublished - 30 Nov 2018

Bibliographical note

Copyright the Author(s) 2018. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.


  • language acquisition
  • individual differences
  • vocabulary size
  • infant-directed speech
  • word recognition


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