The many curious cases of mouses

Error and expectation in language learning: The curious absence of ‘mouses’ in adult speech has just come out in Language, and opens, enticingly enough, with a quote from the Silver Blaze:

Gregory: “Is there any other point to which you would wish to draw my attention?”

Holmes: “To the curious incident of the dog in the nighttime”.

Gregory: “The dog did nothing in the nighttime”.

Holmes: “That was the curious incident”.

–Sir Arthur Conan Doyle

For more puzzles on learning, morphology, and negative evidence, we turn to the abstract:

As children learn their mother tongues, they make systematic errors. For example, English speaking children regularly say “mouses” rather than “mice”. Because children’s errors aren’t explicitly corrected, it has been argued that children could never learn to make the transition to adult language based on the evidence available to them, and thus that learning even simple aspects of grammar is logically impossible without recourse to innate, language specific constraints. Here, we examine the role children’s expectations play in language learning, and present a model of plural noun learning that generates a surprising prediction: At a given point in learning, exposure to regular plurals (e.g. rats) can decrease children’s tendency to overregularize irregular plurals (e.g. mouses). Intriguingly, the model predicts that the same exposure should have the opposite effect earlier in learning. Consistent with this, we show that testing memory for items with regular plural labels contributes to a decrease in irregular plural overregularization in six-year-olds, but an increase in four-year-olds. Our model and results suggest that children’s overregularization errors both arise and resolve themselves as a consequence of the distribution of error in the linguistic environment, and that far from presenting a logical puzzle for learning, they are inevitable consequences of it.