Overextension and underextension in the child's expressive and receptive speech

The tendency of 30 children between the ages of 2; 0 and 2; 1 to overextend and/or underextend newly uttered, but previously understood words in comprehension and production was examined. It was found that both overextensions and underextensions occurred in comprehension and in production. Similarly, in both modes of speech children made more underextensions to peripheral than to central referents, and more overextensions to perceptually similar than to perceptually dissimilar nonreferents. The frequencies of overextensions and underextensions, however, were not the same in comprehension and production. Overextensions occurred more frequently in comprehension than in production, while conversely underextensions occurred more frequently in production than in comprehension. These data are discussed in terms of differences between children's and adult's word meanings, and between comprehension and production.