Non-Nutritive Sucking is Associated with Reduced Word Comprehension: A Longitudinal, Eye-tracking Study

Non-nutritive sucking (NNS), including pacifier use and thumb sucking, is common in infants and has been associated with both positive and negative developmental outcomes. While NNS is known to reduce distress, sustained use has been linked to lower vocabulary scores (Muñoz et al., 2024). The present longitudinal study investigates the relationship between NNS and word comprehension in 69 Norwegian infants. Parents reported their infant’s NNS use concurrently (C-NNS) at 9, 12, 15, and 18 months old, which was used to derive measures of lifespan use (L-NNS) and relative changes in NNS. Word comprehension was measured using eye-tracking, and vocabulary size was assessed through parental reports (CDIs). Neither L-NNS nor changes over time were significantly associated with language measures. However, greater concurrent NNS (C-NNS) correlated with reduced word comprehension in older infants. These findings extend Muñoz et al. (2024) and provide additional evidence on the role of NNS in language acquisition.