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Child language acquisition is a process in which children develop the ability to understand and use language. They are able to do this because they are exposed to language input – language in their environment. By listening to other people speak to them, children can acquire language elements (e.g. words) and patterns (e.g. inflected forms) so that they can use language to communicate and express their needs. Therefore, properties of the input, including “messy” data such as overabundant and defective forms, are of great importance for language acquisition.

In our work we used language experiments, indirect information from parents in the form of a parental questionnaire and naturalistic data. We analysed two languages, Croatian and Estonian. It is known that the properties of the input children are exposed to affect linguistic development, from the frequency of words children hear to the grammatical patterns in which the word forms occur. Croatian has plentiful overabundance within a morphological class, while Estonian has overabundance cutting across inflectional classes.

Using a corpus study we investigated the presence of overabundant forms in the input children hear in the two languages. We then used stimuli based on the child-directed speech in an elicitation experiment to investigate how overabundance is acquired and produced by children. Five-year-old participants in the experiment showed greater accuracy with non-overabundant lexemes, indicating not only that they prefer one available form, but that the presence of parallel forms in CDS may hinder the acquisition of those forms. Lexemes with overabundant morphological paradigms may initially be harder for children to acquire, even while they are producing overgeneralized forms and willing to fill in defective cells. This decreased accuracy is gradually replaced by a target-like use of parallel forms. Accuracy was found to be affected by frequency of word forms and morphological patterns, age and language-specific features like complexity of stem changes.

Certain forms of children's language, known as overgeneralisations (e.g. goed), are similar to overabundant forms in adult language, as children most frequently use both the overgeneralised and the correct form. We investigated how children rely on frequency information from input to recover from this particular phase of dual form use in Croatian language acquisition. Croatian has a complex system of morphological classes. Verbs belonging to the same class show the same pattern of morphological changes. Some patterns are simple, while others have a higher morphological complexity (leading to overgeneralisation). The verb classes differ in frequency, as some classes occur more frequently in the input than others. First, we obtained information about the frequency of verbs and verb classes used by adults when communicating with children from the naturalistic data of child language. On this basis, we developed a questionnaire in which we asked parents of preschool children how often their children produce overgeneralised or correct forms of verbs. Parents of older children reported fewer overgeneralised forms. The frequency of a verb class determines the frequency of overgeneralised forms more than the frequency of individual verbs.

Hržica, G.; Bošnjak Botica, T; Košutar, S. (2023). Stem overgeneralizations in the acquisition of Croatian verbal morphology: Evidence from parental questionnaires. Word Structure 16(2-3), 176-205.