A longitudinal study of the role of vocabulary size on priming effects in early childhood

Studies on lexical development in young children have routinely suggested that the organisation of the early lexicon may change with age and increasing vocabulary size. In the current study, we explicitly examine this suggestion in further detail using a longitudinal study of the development of phonological and semantic priming effects in the same group of toddlers at three different ages. In particular, we examine the extent to which the development of these effects is influenced by the increasing vocabulary size of the child, since our longitudinal design allows us to disentangle the effects of increasing age and vocabulary size. We tested phonological and semantic priming effects in monolingual German infants at 18-, 21- and 24-months-old. We used the intermodal preferential looking paradigm combined with eye tracking to measure the influence of phonologically and semantic related/unrelated primes on target recognition. In addition, Growth Curve Analysis examined the trajectory of infants’ looking behaviour during target recognition. Even after controlling for age at test, both phonological and semantic priming effects were influenced by participants’ receptive and expressive vocabulary size respectively. In particular, children with larger receptive vocabularies showed phonological interference effects, while children with smaller receptive vocabularies showed phonological facilitation effects. With regards to semantic priming, we found an overall semantic interference effect, which was modulated by expressive vocabulary size. These results highlight the fact that vocabulary size is a strong predictor of the development of phonological and semantic priming effects in early childhood, even after controlling for age.