Proceedings of the Annual Meeting of the Cognitive Science Society

Although previous studies have found a link between thequantity and quality of child-directed speech learners receiveand their vocabulary development, no previous studies havefound a parallel link between overheard speech measured ata very young age and vocabulary development (Shneidman& Goldin-Meadow, 2012; Shneidman, Arroyo, Levine, &Goldin-Meadow, 2013; Weisleder & Fernald, 2013). This isdespite the fact that children are able to learn words from over-heard speech in laboratory settings (Shneidman & Woodward,2015). Drawing on the idea that children preferentially at-tend to stimuli that are at a manageable level of complexity(Kidd, Piantadosi, & Aslin, 2012, 2014), the present researchexplores the possibility that children do not initially tune intooverheard speech because it is initially too complex for theirstage of lexical development (i.e., contains too great a propor-tion of unfamiliar words). Using transcripts from CHILDESand the Santa Barbara Corpus, and estimates of vocabularyby age from the MB-CDI, we find that child-directed speechis significantly less complex than overheard speech throughat least 30 months. If attention based on complexity at leastpartially accounts for the statistical independence of overheardspeech and vocabulary development in early childhood, thenchildren might only begin learning from more complex, over-heard speech sometime after 30 months.