Toddlers’ Verb-Marking Errors Are Predicted by the Relative Frequency of Uninflected Sequences in Well-Formed Child-Directed Speech: A Pre-registered Corpus Analysis

Verb-marking errors such as ‘she play football’ and ‘Daddy singing’ are a hallmark feature of English-speaking children’s speech. We investigate the proposal that these errors are input- driven errors of commission, arising from the high relative frequency of subject+unmarked verb sequences in well-formed child-directed speech. We test this proposal via a pre-registered corpus analysis, and ask at what level the effects occur: is it the relative frequency of specific subject+unmarked verb sequences in the input that is important, or is it simply that verbs become entrenched, such that their frequency of appearance with any third-person singular subject accounts for errors? We find that the best predictor of children’s verb-marking errors is the relative frequency of unmarked forms of specific subject+verb sequences. Our results support the proposal that children's apparent omissions of certain grammatical morphemes are in fact input- driven errors of commission and provide insight into the mechanisms by which this occurs.