Effects of input rate and age on the real-time language processing of children with specific language impairment.

Background: School-age children with specific language impairment (SLI) exhibit slower real-time (i.e. immediate) language processing relative to same-age peers. The offline sentence comprehension of children with SLI can be improved when the input is slowed down. Although this finding suggests that a slower input delivery facilitates these children's language processing, such an interpretation is premature, as there are no data directly addressing the issue. Additionally, while typically developing (TD) children demonstrate age-related improvements in language processing (i.e. they become faster processors), it is unclear whether children with SLI show the same developmental improvement.

Aims: It was investigated whether a reduced input rate can enhance the online language processing of children with SLI. If it does, their reaction time (RT) for recognizing words embedded in sentences delivered at a slow rate should be faster relative to words in normal- and fast-rate sentences. For TD children, RT should be unaffected by rate manipulation, as their language-processing system is sufficiently robust to handle such a simple input manipulation. A secondary aim was to provide preliminary data on the developmental course of language processing proficiency in children with SLI.

Methods And Procedures: Twenty school-age children with SLI and 20 age-matched TD children completed a word recognition RT task. Children monitored simple sentences for a target word and made a timed response immediately upon recognizing the target. Sentences were presented at 'normal', 'slow' and 'fast' speaking rates.

Outcomes And Results: There was a significant group by input rate interaction. Children with SLI, relative to TD peers, yielded significantly slower RT for normal- and fast-rate sentences, but faster RT for slow-rate sentences. Within-group analyses showed the children with SLI produced the fastest RT for slow-rate sentences and the slowest RT for fast-rate sentences. The TD children showed the opposite response pattern: the fastest RT for fast-rate sentences and the slowest RT for slow-rate sentences. Age also had a significant effect. Regardless of language status, older children produced faster RT than younger children. Interestingly, even the oldest children with SLI still demonstrated significantly slower RT than the youngest TD children.

Conclusions: The real-time language processing of children with SLI can be facilitated when the material is presented at a slower rate. A slower rate apparently allows these children time to allocate their attentional resources more effectively to the various processing operations supporting comprehension. Additionally, the language proficiency of children with SLI improves with age. However, older children with SLI are still slower than their youngest TD peers, suggesting that the language-processing apparatus of children with SLI operates even more inefficiently than what their receptive language knowledge might otherwise predict.