Sources of variation in developmental language disorders: evidence from eye-tracking studies of sentence production

Courtenay Frazier Norbury 0 0 Department of Psychology, Royal Holloway, University of London , Egham, Surrey TW20 0EX , UK Articles on similar topics can be found in the following collections Receive free email alerts when new articles cite this article - sign up in the box at the top right-hand corner of the article or click here - Subject collections Email alerting service rstb.royalsocietypublishing.org Review Cite this article: Norbury CF. 2014 Sources of variation in developmental language disorders: evidence from eye-tracking studies of sentence production. Phil. Trans. R. Soc. B 369: 20120393. http://dx.doi.org/10.1098/rstb.2012.0393 One contribution of 17 to a Discussion Meeting Issue Language in developmental and acquired disorders: converging evidence for models of language representation in the brain. Author for correspondence: Courtenay Frazier Norbury e-mail: Electronic supplementary material is available at http://dx.doi.org/10.1098/rstb.2012.0393 or via http://rstb.royalsocietypublishing.org. Sources of variation in developmental language disorders: evidence from eyetracking studies of sentence production Courtenay Frazier Norbury Skilled sentence production involves distinct stages of message conceptualization (deciding what to talk about) and message formulation (deciding how to talk about it). Eye-movement paradigms provide a mechanism for observing how speakers accomplish these aspects of production in real time. These methods have recently been applied to children with autism spectrum disorder (ASD) and specific language impairment (LI) in an effort to reveal qualitative differences between groups in sentence production processes. Findings support a multiple-deficit account in which language production is influenced not only by lexical and syntactic constraints, but also by variation in attention control, inhibition and social competence. Thus, children with ASD are especially vulnerable to atypical patterns of visual inspection and verbal utterance. The potential to influence attentional focus and prime appropriate language structures are considered as a mechanism for facilitating language adaptation and learning. 1. Introduction Speaking in sentences is a momentous developmental milestone that marks the beginning of a childs ability to communicate an infinite array of ideas, feelings and experiences, past and present, real or imagined, to other people. Intuitively, this seems an effortless development for most children, yet producing a fluent and meaningful utterance is a complex process. Models of skilled, adult sentence production outline at least three key processes: conceptualization, formulation and articulation [1]. Conceptualization is the stage at which speakers decide on the message to be conveyed. Formulation requires that speakers map that intended message onto word forms (lexicalization) and particular word orders (syntactic planning). Finally, the speaker must plan and make the motor movements necessary to articulate the message. The vast majority of children will begin to master this complex process in the preschool years. For those with neurodevelopmental disorders, however, language production may present lifelong challenges. Until recently though, we have known little about where in the processing chain language breaks down and how identifying points of difficulty may inform potential intervention strategies. Traditionally, psychologists and linguistics have had to rely on the product of this processing chain to infer the prerequisites needed at each stage for successful production [2]. What skilled speakers say, and importantly the timing of production elements and the errors that speakers make, have provided insights into processing mechanisms and informed computational models of how meaning is translated into the syntax of a particular language [3]. Such models have also made inroads into our understanding of how children become competent syntactic speakers. These models highlight the importance of experience-dependent and error-based learning mechanisms that are shaped by the innate (neural) architecture of the developing system [4]. For most young children, experience is socially mediated; children learn from their interactions with caregivers and very quickly can adapt their language production to their listening audience. Thus, typical children become competent speakers by evaluating their actual or & 2013 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0/, which permits unrestricted use, provided the original author and source are credited. intended outputs against expectations derived from linguistic input [4] and the social conventions shared by interlocutors [5]. What speakers say, however, will only take us so far. Analysing speech output tells us relatively little about the process of conceptualization, for instance, how do people decide what to talk about and how do children learn to create utterances that are relevant to context and to listener need? How is the form of the intended message constrained by individual differences in the developing system, by for instance, limited vocabulary or reduced memory capacity? This question assumes particular relevance when considering language development in atypical populations; similar output may arise from qualitatively different underlying processing mechanisms (cf. [6]). Recent advances in eye-tracking technology may elucidate these processes in new ways, by taking advantage of the fact that eye-movements are temporally linked to verbal output [7], and thus can reveal more about the processes involved in conceptualization, formulation and articulation of utterances, as they occur. This paper therefore considers the application of eye-tracking paradigms to investigate language production in two common neurodevelopmental disorders, autism spectrum disorder (ASD) and developmental language impairment (LI). The goal of the research programme is to elucidate any qualitative differences between these two populations in the conceptualization and formulation of sentences. The work builds extensively on adult models of sentence processing, but yields novel insights into the multiple factors that contribute to language development and disorder. The paper begins by considering what is known from previous eye-tracking studies about language production processes in skilled adult speakers and young typically developing speakers. Then, language production in ASD and LI and the potential advantages of using eye-movements to reveal continuities and discontinuities in the language processing of these populations is discussed. Finally, four case studies of eye-movements and language production in children with typical development (TD), ASD and LI are provided, highlighting possible sources of language breakdown and hinting at future intervention strategies. 2. Eye-tracking as a (...truncated)