Stokes, S.
University of Canterbury, New Zealand
Word learning in infants and toddlers is a contemporary topic in developmental science, but the mechanisms that underpin typical lexical development are not well understood, and those of slower learners even less so. Phonological neighborhood density (ND) is a statistical cue that toddlers harness to create an expressive lexicon. Recent research showed that ND accounted for 47%, 53% and 39% of the variance in expressive vocabulary size for English-, French-, and Danish-speaking toddlers. High ND words are composed of onsets, rhymes and consonants that are repeated across words (CV#, such as cat, cap; #VC, such as cat, hat; C1#C2, such as cat, cot). High ND words are less taxing on toddlers' short-term memory systems than low ND words. Toddlers who struggle to learn an expressive lexicon (late talkers, LTs) have reduced short-term memory abilities relative to their typically developing (TD) peers. The Extended Statistical Learning (ExSL) account, proposed as an explanation for slow vocabulary development in LTs, claimed that LTs continued to harness high ND cues because they were unable to abstract low ND cues from the ambient language, with subsequent difficulty forming representations for sparse words. The current research tested the ExSL account by examining whether the ACTIVE (words said and understood) and PASSIVE (words understood, NOT said) lexicons of LTs differed from those of TD children on phonological ND. The ACTIVE and PASSIVE lexicons of 120 toddlers aged 17-24 months were coded for ND values. There was no significant difference between the LT's and TD children's PASSIVE lexicons in ND, but the average ND of LT's ACTIVE lexicons was significantly higher than that of the TD children. The results only partially support the ExSL account. LTs can form at least partial phonological representations for sparse words, but they cannot activate these representations for word production.