Infant temperament predicts early communicative skills in the FinnBrain Birth Cohort Study

Studies have established that dimensions of temperament and language development are associated in childhood. Insofar, however, longitudinal studies from infancy into toddlerhood accounting for all temperament dimensions and covering preverbal communication in addition to emerging verbal skills are scarce. Existing findings are inconclusive.The current study is an extension of our previous study (N = 91) on a large cohort sample (N = 1200 and 1039 depending on analysis). Temperament (positive emotionality, negative emotionality and emerging self-regulation) was assessed at 6 and 12 months of age and gesturing and receptive vocabulary at 14 months. As an extension to the previous study, expressive vocabulary and sentence complexity in toddlerhood, at 30 months, were also assessed. All assessments utilized parent reports.The temperament traits of positive emotionality and self-regulation positively predicted all communicative skills except sentence complexity. Positive emotionality accounted for 10-11% of the variance in gesturing, 4-5% in receptive vocabulary and 1-3% in expressive vocabulary. Self-regulation accounted for 4-6% of the variance in gesturing, 2-3% in receptive vocabulary and 0-1% in expressive vocabulary.Results aligned with the findings of our prior study but also highlighted weak longitudinal positive associations between positive emotionality and self-regulation and gesturing and vocabulary. However, associations were notably stronger with gesturing compared to verbal skills, suggesting temperament and preverbal communication are intertwined on a higher level compared to verbal skills. Longitudinal weakening of associations suggests the role of infant temperament is replaced by other factors influencing language development moving into toddlerhood.