The impact of lexical frequency on sentence comprehension in children with specific language impairment

Children with SLI generally exhibit poor sentence comprehension skills. We examined the
specific impact of grammatical complexity and lexical frequency on comprehension
performance, yielding contrasting results. The present study sheds new light on sentence
comprehension in children with SLI by investigating a linguistic factor which has attracted
little research interest: the impact of the lexical frequency of known words on sentence
comprehension. We also examined the impact of grammatical complexity and sentence
length by independently varying these two factors. Fifteen children with SLI, 15 age- and
IQ-matched controls, and 15 controls matched on lexical and grammatical skills,
performed sentence comprehension tasks in which three linguistic factors were
manipulated: lexical frequency (sentences containing words of either low or high lexical
frequency), grammatical complexity (sentence containing either a subject relative clause
or an object relative clause) and sentence length (either short or long sentences). Results
indicated that children with SLI performed more poorly overall compared to age- and IQmatched
children and to lexical and morphosyntactic age-matched children. However,
their performance was not more affected by either sentence length or clause type than that
of control children. Only lexical frequency affected sentence comprehension to a greater
extent in children with SLI relative to the control groups, revealing that SLI children’s
sentence comprehension abilities are particularly affected by the presence of lowfrequency
but familiar words.