This article presents a theoretical framework designed to accommodate core evidence that the abilities to repeat nonwords and to learn the phonological forms of new words are closely linked. Basic findings relating nonword repetition and word learning both in typical samples of children and adults and in individuals with disorders of language learning are described. The theoretical analysis of this evidence is organized around the following claims: first, that nonword repetition and word learning both rely on phonological storage; second, that they are both multiply determined, constrained also by auditory, phonological, and speech–motor output processes; third, that a phonological storage deficit alone may not be sufficient to impair language learning to a substantial degree. It is concluded that word learning mediated by temporary phonological storage is a primitive learning mechanism that is particularly important in the early stages of acquiring a language, but remains available to support word learning across the life span.

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).

Individual differences in nonword repetition (NWR) show a particularly strong association with vocabulary acquisition for both first- (L1) and second-language (L2) learners, and they serve as a behavioral marker for specific language impairment (SLI) in children (Gathercole, 2006). However, this association is susceptible to alternative explanations.

In line with the original presentation of nonword repetition as a measure of phonological short-term memory (Gathercole & Baddeley, 1989), the theoretical account Gathercole (2006) puts forward in her Keynote Article focuses on phonological storage as the key capacity common to nonword repetition and vocabulary acquisition. However, evidence that nonword repetition is influenced by a variety of factors other than item length has led Gathercole to qualify this account. In line with arguments put forward by Snowling, Chiat, and Hulme (1991), one of Gathercole's current claims is that nonword repetition and word learning are constrained by “the quality of temporary storage of phonological representations, and this quality is multiply determined.” Phonological storage is not just a quantity-limited capacity.

In her Keynote Article, Gathercole (2006) presents a theoretical framework intended to account for evidence regarding the relation between nonword repetition and word learning. This framework stems from an impressive amount and breadth of research on this topic, including findings from adults and children with typical language abilities as well as language learning disorders. In this commentary we focus on claims relative to the interpretation of nonword repetition deficits in children with specific language impairment (SLI). One issue we address pertains to the nature of the proposed model of nonword processing and word learning, particularly with respect to phonological sensitivity and storage. The second issue we address relates to the assumption that a phonological storage deficit, although not sufficient, is necessary for SLI.

Our understanding the relationship between verbal short-term memory as indexed by nonword repetition and word learning must now incorporate myriad factors that were not as apparent 17 years ago when Gathercole and Baddeley (1989) proposed that “the phonological memory skills tapped by nonword repetition play a causal role in vocabulary development” (p. 211). In particular, successful nonword repetition involves more than the phonological loop, word learning happens by degrees, and is influenced by many factors other than phonology, and children with specific language impairment (SLI), who have served as test cases by virtue of consistently demonstrating phonological memory deficits, often exhibit other deficits with the potential to negatively impact word learning. Gathercole (2006) still makes the case for temporary phonological storage playing an important role in word learning, but with several caveats. I would like to add two.

The proposals that (a) nonword repetition and word learning both rely on phonological storage and (b) both are multiply determined are two of the major foci of Gathercole's (2006) Keynote Article, which marshals considerable evidence in support of each. In my view, the importance of these proposals cannot be overstated: these two notions go to the heart of the relationship between nonword repetition and word learning. Indeed, they figure prominently in the approach that my colleagues and I have taken to studying that relationship (e.g., Gupta, 2006; Gupta, Lipinski, Abbs, & Lin, 2005; Gupta & MacWhinney, 1997). An important aspect of our approach has been the attempt to construct a computational model that can simulate performance in a nonword repetition task and in a word learning task, the rationale being that a computational model that achieved this would constitute a proposal about the processing mechanisms that may underlie the relationship. In this Commentary, I describe how our computational work offers a concrete way of thinking about how nonword repetition and word learning may rely on phonological storage, and about how these abilities may be multiply determined. Such computational work is, I suggest, a valuable tool in further investigating the important relationship that has been revealed by Gathercole's influential work, and that is analyzed in the Keynote Article.

This Commentary supports Gathercole's (2006) proposal on a double deficit in children with specific language impairment (SLI). The author suggests that these children have a limited phonological storage combined with a particular problem of processing novel speech stimuli. According to Gathercole, there are three areas of skill contributing to memory for nonwords: general cognitive abilities, phonological storage, and an unidentified skill specific to nonword repetition. The focus of this Commentary is to examine whether these children's nonword repetition performance is influenced by an unidentified skill or some other processes. An alternative hypothesis is that the nonword repetition errors observed in children with SLI are related to one of their main weaknesses, to their difficulties in simultaneous processing of information. Evidence for this argument comes from our recent studies: from error analyses data and from findings on nonword repetition with stimuli that included meaningful parts (monosyllabic real words).

In her Keynote, Gathercole (2006) provides a comprehensive review regarding the nature of the nonword repetition (NWR) task and a compelling argument for the utility of the task as a robust index of children's phonological short-term storage capacity. She further argues that temporary phonological storage acts as a primitive learning mechanism that plays an instrumental role in the lexical learning of young children, including children with specific language impairment (SLI). In this Commentary, we focus our remarks on two related themes concerning the relation of NWR and SLI: (a) performance on NWR tasks provides a window into these children's more general cognitive (dis)abilities and (b) the robustness of NWR as a predictor of these children's lexical knowledge and learning abilities.

Susan Gathercole's Keynote Article (2006) is an impressive summary of the literature on nonword repetition and its relationship to word learning and vocabulary size. When considering research by Mary Beckman, Jan Edwards, and myself, Gathercole speculates that our finding of a stronger relationship between vocabulary measures and repetition accuracy for low-frequency sequences than for high-frequency sequences is due to differences in the range of the two measures. In our work on diphone repetition (e.g., Edwards, Beckman, & Munson, 2004; Munson, Edwards, & Beckman, 2005) we tried to increase the range in our dependent measures by coding errors on a finer grained scale than simple correct/incorrect scoring would allow. Moreover, restriction of range does not appear to be the driving factor in the relationship between vocabulary size and the difference between high- and low-frequency sequence repetition accuracy (what we call the frequency effect) in at least one of our studies (Munson et al., 2005). When the children with the 50 lowest mean accuracy scores for high-frequency sequences were examined, vocabulary size accounted for 10.5% of the variance in the frequency effect beyond what was accounted for by chronological age. When the 50 children with the highest mean accuracy scores for high-frequency sequences were examined (a group in which the range of high-frequency accuracy scores was more compressed, arguably reflecting ceiling effects), an estimate of vocabulary size accounted for only 6.9% of the frequency effect beyond chronological age. The associated β coefficient was significant only at the α<0.08 level. This is the opposite pattern than Gathercole's argument would predict.

The first report of a connection between vocabulary learning and phonological short-term memory was published in 1988 (Baddeley, Papagno, & Vallar, 1988). At that time, both Susan Gathercole and I were involved in longitudinal studies, investigating the relation between nonword repetition and language learning. We both found a connection. Now, almost 20 years later, in her Keynote Gathercole (2006) reviews a multitude of data bearing on the interpretation of this often replicated connection. Her main conclusions are three. First, both nonword repetition and word learning are constrained by the quality of temporary storage. She sees this storage as multiply determined, that is, affected by factors like perceptual analysis, phonological awareness (ability to identify and reflect on the speech sounds that make up words). Second, both nonword repetition and word learning are also affected by sensory, cognitive, and motor processes. Third, an impairment of phonological storage is typically associated with specific language impairment (SLI) but may not be a sole causal factor.

Using nonword repetition tasks as an experimental approach with both adults and children has become quite common in the past 10 to 15 years for studying lexical learning and phonological processing (e.g., Bailey & Hahn, 2001; Gathercole, Frankish, Pickering & Peaker, 1998; Munson, Edwards, & Beckman, 2005; Storkel, 2001; Vitevich & Luce, 2005). In her Keynote, Gathercole (2006) indicates that “The ability to repeat multisyllabic nonwords…probably represents the most effective predictor of language learning ability that is currently known” and that “nonword repetition…may also hold the key to understanding developmental disorders of language learning.” Her Keynote reviews many of the findings from a variety of nonword repetition studies with typically developing children and children with specific language impairment (SLI) or other language-related disorders. Despite the substantial benefits and interesting findings that nonword test paradigms have provided in addressing different issues, a number of questions and precautions should be kept in mind regarding such approaches. Researchers who routinely employ these procedures are likely to be well aware of these issues, and in fact, Gathercole points out some of the limitations. For those less familiar with nonword repetition tasks, it seems advisable to reinforce the need for a certain amount of caution in evaluating the results of such approaches.

In 1990 Gathercole and Baddeley proposed a strong hypothesis that has generated a wealth of research in the field of language development and disorder. The hypothesis was that phonological memory, as indexed by nonword repetition, is causally related to vocabulary development. Support for the hypothesis came from an impressive range of longitudinal, correlational, and laboratory training studies, and from studies of specific language impairment (SLI). However, more recently, Gathercole, Tiffany, Briscoe, Thorn, and The ALSPAC Team (2005), directly tested the causal hypothesis by following a cohort of children from age 5 to 8 years. Contrary to prediction, children with poor nonword repetition abilities at age 5 had normal vocabulary at the age of 8.

Gathercole's (2006) comprehensive and interesting Keynote Article on the nature of the relations between nonword repetition and word learning highlights the complex number of interacting factors that affect this relation through development. In this Commentary we focus on the impact of higher level cognition, particularly linguistic representations on lower level functions such as attention and processing, as well as higher level functions such as memory. In addition, we note the importance of distinguishing children with specific language impairment (SLI) who do and do not have phonological deficit when testing for memory impairments. We argue that further detailed investigations are warranted at the linguistic levels of cognitive processing alongside memory tasks that tap different components of language and nonlinguistic memory. Such studies would help tease apart the complex, and probably bidirectional relations between attention, memory, and linguistic representations. Moreover, we propose that this investigative strategy crucially needs to take a longitudinal developmental perspective if we are to understand the developmental trajectory.

The work of Susan Gathercole and others on nonword repetition has increased general interest in the relationship between memory and language, and has provided a fertile theoretical framework for researchers to explore how the language system makes use of the phonological loop, a component in Baddeley's (1986) working memory model. Gathercole (2006) integrated a number of findings from a variety of research methodologies and populations to support this theoretical framework. She also discussed how this framework might be applied to increase our understanding of language disorders characterized by word learning problems. Synthesizing the findings from many and diverse areas of study to formulate a coherent theory is a challenge, but this challenge must be undertaken if we hope to significantly advance our understanding of human behavior, including the differences in processing that are found across the lifespan and across individuals. I admire Gathercole for undertaking this challenge (and the additional challenge of applying the theory to language disorders) in the area of word learning.

Because words represent the building blocks upon which the facility to produce and comprehend language at all levels is based, the capacity of a child to learn words has immense impact on his or her developing abilities to communicate and engage properly with the outside world. Both the Keynote Article and the Commentaries in this issue demonstrate that this capacity to acquire vocabulary is neither singular nor simple. Children may fail to learn new words in as rapid and efficient manner as their peers for many reasons: they may, for example, have inadequate environmental experience of either the spoken and printed form of the language (Huttenlocher, Haight, Bryk, Seltzer, & Lyons, 1991), or they may have poor abilities to produce the sound contrasts of the language (Mirak & Rescorla, 1998). The focus of the present discussion lies somewhere in between these extremes of influence, in the intervening perceptual and cognitive processes that constitute the speech processing and word learning system. Here, too, complexities abound. The developing language system is characterized by dependencies between the multiple processes involved in processing and learning language (Bishop, 1997), rarely evincing the dramatic dissociations in adults with acquired language disorders that have served cognitive neuropsychology so well in its bid to identify a modular structure of the language system. Weaknesses in perceptual analysis of the sound structure of the language, in the storage of the resulting mental representations, and in the availability of existing representations that can support the processing of new words, often coexist within an individual. As a consequence, it can be extremely difficult to tease apart the developmental underpinnings of language acquisition. In this article, I argue that real progress toward understanding vocabulary acquisition requires a substantial and systematic body of research evidence designed to provide strong empirical challenges to existing (and new) hypotheses and theories. Whereas mere description is unlikely to lead to major advances, systematic experimental analysis and the specification of detailed theoretical accounts should result in a more complete understanding of the complexities and constraints of new word learning.