Grammaticality judgements in adolescents with and without language impairment

Existing evidence suggests that young children with specific language impairment have unusual difficulty in detecting omissions of obligatory tense-marking morphemes, but little is known about adolescents' sensitivity to such violations.

The study investigated whether limitations in receptive morphosyntax (as measured by grammaticality judgements) were present at age 16 years, and, if so, whether participants' profiles showed less sensitivity to omissions of tense and agreement morphemes than to (1) inappropriate uses (intrusions) of these same morphemes, and (2) omissions of morphemes that do not encode tense and agreement. The study also compared adolescents with language impairment and non-verbal IQ more than 1 standard deviation (SD) below the mean (nonspecific language impairment) to adolescents with specific language impairment.

Adolescents with specific language impairment (n = 48), adolescents with non-specific language impairment (n = 25), and adolescents with normal language development (n = 108) performed speeded grammaticality judgements of sentences presented over headphones. Half the sentences were ungrammatical. They included omissions of non-tense morphemes (-ing and possessive -s), omissions of tense morphemes (-ed and third-person singular present -s), and intrusions of the same tense morphemes. The A' statistic was used as the dependent variable for comparisons across groups and item types.

Overall, the normal language development group was more sensitive to grammatical violations than the specific language impairment and non-specific language impairment groups, and there was no significant interaction of group and item type. Post-hoc analyses showed that the specific language impairment group was less sensitive to violations than the normal language development group on each item type, and the specific language impairment and non-specific language impairment groups did not differ. Across groups, performance on omission of past tense -ed was lowest, and properties of the items that may have contributed to this difference were explored.

The adolescents with language impairment in this study showed evidence of reduced sensitivity to morphological errors, including both tense-marking and non-tense-marking morphemes, but no evidence of any extraordinary difficulty in detecting the omission of tense-marking morphemes, in contrast to results from other research on younger children with specific language impairment. Participants whose non-verbal IQ score was too low to meet the criteria for specific language impairment performed similarly to their peers with specific language impairment. Grammatical competence is compromised in these adolescents with specific language impairment and non-specific language impairment. Neither researchers nor clinicians can assume that adolescents with language impairment have fully mastered grammatical morphology.