Beyond words: Phonological short-term memory and syntactic impairment in specific language impairment

The assessment of nonword repetition in children goes back at least to 1974, when the Goldman–Fristoe–Woodcock Auditory Skills Battery was published, including a subtest (Sound Mimicry) assessing nonword repetition (Goldman, Fristoe, & Woodcock, 1974). Nevertheless, it was not until 20 years later, when Gathercole and Baddeley (1990) reported a study of short-term memory in children with specific language impairment (SLI), that a theoretical framework was developed linking deficits in nonword repetition to impaired language acquisition. Gathercole’s Keynote in this issue (2006) tells the story of how this initial study revealed a striking nonword repetition deficit in children with SLI, complementing work on typically developing children showing a major role of phonological short-term memory (STM) in word learning. As she points out, the story is a complex one: phonological STM is not the only skill tapped by the nonword repetition task, and children may do poorly for different reasons. Furthermore, relationships between nonword repetition and word learning may be reciprocal, with vocabulary level affecting children’s ability to segment nonwords efficiently and retain them in memory. However, the original finding, that deficient nonword repetition is a strong correlate of SLI, has stood the test of time, to the extent that poor performance on this test has been used successfully as a marker of a heritable phenotype in molecular genetic studies of SLI (Newbury, Monaco, & Bishop, 2005). According to the theoretical framework presented by Gathercole (2006), word learning should proceed slowly in SLI, and this is indeed usually the case. Nevertheless, for most children, vocabulary is less impaired than syntax (see Leonard, 1998, for review). This raises the question of whether phonological STM is implicated in acquisition of syntax as well as vocabulary. This issue was raised in 1998 by Baddeley, Gathercole, and Papagno, who presented a theory of the phonological loop as a language learning device, arguing that the ability to retain small amounts of phonological information in STM evolved as a human characteristic that had selection advantage because it facilitated language acquisition. In that paper they reviewed evidence that, in typically developing children, nonword repetition, a measure of phonological loop capacity, was related not only to vocabulary learning but also to acquisition of syntax. This theoretical account was attractive to those working on SLI, because it suggested that a deficit in a single specialized memory system could potentially account for the whole gamut of linguistic deficits seen in language-impaired children, without needing to invoke domain-specific impairment of specialized