A curvilinear trend in naming errors as a function of early vocabulary growth.

This research examines changes in word retrieval and naming during a developmental period in which there is a substantial increase in productive vocabulary. That increase generally occurs when children have between 50 to 150 words in productive vocabulary. We examined children's naming errors in two studies for what these errors could tell us about the emerging lexicon. The method we used for eliciting spontaneous naming was picture book reading by the parent. In Experiment 1, 12 children were followed longitudinally at three-week intervals from 15 to 22 months. Parent diaries were used as a measure of vocabulary growth. Experiment 2 used a cross-sectional design to compare the naming errors of 60 children assigned to one of three vocabulary ranges. Measures of vocabulary size were based on the MacArthur Communicative Development Inventory. In both experiments we found a sharp increase in naming errors in the picture book task that was coincident with sudden changes in productive vocabulary. These naming errors were often perseverative in nature and appear to reflect interference in the retrieval process from previously retrieved words. The results suggest that these errors in naming are a consequence of changes in lexical processing that occur with rapid growth of productive vocabulary and concurrent increased rates of speaking.