Verb production by individuals with Down syndrome during narration.

The intellectual disability group had higher nonverbal cognitive ability than the Down syndrome and typically developing groups, so the groups were not fully matched on that variable. Verb coding counted any verb used in story-relevant speech, even if it was not grammatically or semantically correct, so it does not show accuracy. The relationship between verb production and sentence length was measured from the same narration task, and correlations do not show that verb problems cause syntax problems. The study included only English-speaking participants, so the pattern may not apply to other languages. The intellectual disability group included participants with fragile X syndrome, which may have influenced that comparison. This was the first study to compare verb production in Down syndrome with mixed-etiology intellectual disability, so replication is needed. The age ranges in the Down syndrome and intellectual disability groups were wide, although age was not correlated with the verb outcomes in the Down syndrome group.

Do not conclude that verb production is a Down syndrome-specific deficit relative to other intellectual disability. Verb density was not significantly different between the Down syndrome and mixed-etiology intellectual disability groups, and verb diversity was not different among groups.