Purpose: Relative to their age peers, children with specific language impairment (SLI) demonstrate significantly greater difficulty processing and comprehending verbal be passive and object relative sentences, but not subject-verb-object (SVO) sentences. Children with SLI also consistently evidence reduced phonological short-term memory (pSTM) and slower processing speed. This project examined the potential association between these SLI characteristics by attempting to simulate the complex sentence comprehension problems in a group of typically developing children by inducing difficulty comprehending sentences involving syntactic movement (van der Lely, 2005).
Method: Thirty six 7- to 11-year-old children completed a real-time sentence comprehension task in which they selected the agent of the sentence. Sentence comprehension was made harder by introducing two stress factors, sentence length and input rate (designed to stress pSTM and speed of language processing), to passive, object relative, and SVO sentences. Children received equal numbers of 9-, 12-, and 15-word sentences of each sentence type blocked by normal rate, 20% faster rate, and 33% faster rate. The primary dependent variables were sentence comprehension accuracy and speed. The separate effects of sentence length and input rate were of central interest.
Results: The effect of sentence length on comprehension accuracy was not significant for any sentence type. Sentence length did significantly affect speed of comprehension, with processing of 12- and 15-word sentences being comprehended significantly faster than 9-word sentences. Input rate had no significant effect on the comprehension accuracy of any sentence type. However, speed of comprehension was significantly affected by input rate, with 33% rate compressed passive and object relative sentences being comprehended significantly more slowly relative to at least one of the other input rate sentences.
Conclusions: In typically developing children, increasing sentence length (and by extension stressing pSTM) did not induce poorer complex sentence comprehension that is characteristic of children with SLI. Increasing input rate (and, by extension, taxing language processing speed) did lead to slower speed of comprehension of complex sentences, but it did not impair comprehension accuracy. The children demonstrated a clear speed-accuracy tradeoff, sacrificing speed for accuracy.