The leading-edge: the significance of sentence disruptions in the development of grammar.

This research explored the relationship between sentence disruptions and the length and complexity of sentences spoken by children developing grammar. The study was cross-sectional in design and used samples of naturalistic, conversational interaction between 26 typically developing children (ages 2;6 to 4;0) and a primary caregiver. The active, declarative sentences produced by these children were coded for the presence of disruption, length in morphemes and words, and clausal complexity. The results showed that, for the majority of the children, disrupted sentences tended to be longer and more complex than fluent sentences. The magnitude of the differences in length and complexity was positively correlated with the children's grammatical development, as measured by the Index of Productive Syntax. It was also found that differences between the average complexity of disrupted versus fluent sentences increased with grammatical development even when sentence length was held constant. As grammatical development proceeded, disrupted sentences were more apt to be sentences on the "leading-edge" of the child's production capacity. Although these more advanced grammatical structures are part of the child's grammatical competence, the child cannot produce these sentences without an increased risk of processing difficulty. The results are congruent with proposals concerning the incremental and procedural nature of adult sentence production.