Toddlers with delayed expressive language: An overview of the characteristics, risk factors and language outcomes

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• Expressive language delay is an increasingly important area in language learning disabilities (Rescorla, 2011). This article provides an overview of research findings on expressive language delay and is divided into four sections. The first section considers late talker's language profile by focusing on language and communication skills as well as behavioral and socio-emotional development. The second section addresses the intrinsic and extrinsic factors that appear to contribute to the delayed onset and progression of children's expressive language. The third section concerns language outcomes of late talking. Finally, the paper concludes by summarizing language outcomes of late talking toddlers at a later stage in development and clinical guidelines for educators and clinicians. Within the field of atypical language development, the terms ‘late talkers’ or ‘children with expressive language delay’ or ‘children with late language emergence’ are used to describe toddlers who developmentally lag behind in certain aspects of language, such as vocabulary, phonology or syntax (Kelly, 1998, Rescorla and Lee, 1999). Late talkers are children 18–35 months old who acquire language at a slower rate than their typically developing peers. These children have limited expressive vocabulary and/or receptive language, provided they do not have any other deficits, such as cognitive, neurological, socio-emotional, or even a sensory deficit (Rescorla, 1989, Thal, 2000). Some late talkers manage to catch up to their typically developing peers while others do not. It is of great clinical importance to better understand how to differentiate these children early on. The purpose of this manuscript is to review what recent research currently suggests about the differences between these groups with the ultimate aim of providing clinical guidance (evidence-based practice). Over the last three decades, much research has been conducted on children with expressive language difficulties (see, for example, Ellis and Thal, 2008, Henrichs et al., 2011, Paul and Roth, 2011, Rice et al., 2008). Expressive language delay, the primary difficulty of late talkers, is a common symptom of many syndromes associated with speech and language problems, such as intellectual disability or autism spectrum disorder (Rescorla, 2011). This makes differential diagnosis of late talkers a rather challenging task for researchers and clinicians alike. Heterogeneity in research in early expressive language delay diagnosis, in terms of identification criteria and clinical samples, has led to the distinction of two types of developmental trajectories for language delay, late producers and late comprehenders (Ellis and Thal, 2008, Leonard, 2009). The former term refers to children with delayed expressive vocabulary skills, whereas the latter to children with delays in both expressive and receptive language. In the 1980s and 1990s, a number of longitudinal studies used as identification criteria for early language delay two or more standard deviations below the mean on a measure of expressive language (e.g. Paul, 1991) or a cutoff of 50 words on a parent report of toddler's expressive language (Fenson et al., 1993). These studies included children who had an attested expressive delay but normal receptive vocabulary or receptive vocabulary varying in relation to expressive (Desmarais, Sylvestre, Meyer, Bairati, & Rouleau, 2008). A small subset of studies in the late 1990s (see Thal, 2000) and many studies in the 2000s (Paul and Roth, 2011) stress the strong predictive value of receptive abilities. They tend to measure systematically receptive vocabulary in conjunction with the use of communicative gestures such as pointing (Chiat and Roy, 2008, Olswang et al., 1998). So, variations in the identification procedures utilized across both small- and large-scale studies of late talkers reflect the descriptive character of the diagnostic category of late talkers. Approximately 15% of children at the age of 2 present slow onset and progression of expressive language (Desmarais et al., 2008, Horwitz et al., 2003). In 18–23 month-old toddlers, the percentage of late talkers is estimated to be around 13.5%, whereas in 30–36 month-old toddlers the rate rises to 17.5% (Horwitz et al., 2003). In order to identify late talkers, researchers often use parent report measures of expressive vocabulary such as the Language Development Survey (LDS, Rescorla, 1989) or the MacArthur-Bates Communicative Development Inventory (CDI, Fenson et al., 1993, Fenson et al., 2007). In Rescorla and Achenbach's (2002) study, the criteria for identifying a late talker between 18 and 23 months of age included a performance below the 15th percentile on the LDS, which is converted to an expressive vocabulary of 20 words or less. On the CDI, a 24-month toddler is considered a late talker if the average number of words included in her expressive vocabulary is equivalent to the 10th percentile or below (Ellis Weismer, 2007). These differences in diagnostic criteria eventually obscure data. In particular, by the age of 24 months, girls with expressive language delay are more likely to use approximately 92 words out of 680 which are included on the CDI. On the other hand, by the same age, boys’ expressive vocabulary appears to be limited to 63 words (Roos & Weismer, 2008). A large-scale study by Zubrick, Taylor, Rice, and Slegers (2007) found that male children are three times more likely to have language delay compared with females. Horwitz et al. (2003) found that males between 12 and 17 months tend to have statistically significantly lower expressive language performance than girls. However, some researchers criticize the diagnosis of language delay at such early age on the grounds of lexicon size. According to Paul (1996), the development of a normal vocabulary range takes place by the age of 24 months, but not earlier. Kelly (1998) pointed out that the growth rate of vocabulary of a typically developing child tends to slow down between 18 and 24 months. These facts should be taken under consideration when attempting to identify a toddler younger than 24 months as a late talker. Most studies in the field of late talking have focused either on the short- or on the long-term growth outcomes across different dimensions of language. In particular, small-scale longitudinal studies attempted to trace language growth in the preschool period, whereas others have focused on school-age children with language impairments. These studies have indicated that the majority of late talkers scored in the normal range on vocabulary measures by the age of 3, and in the normal range of grammar and conversational skills by school age (Ellis and Thal, 2008, Domsch et al., 2012, Rescorla, 2011, Rice et al., 2008). However, even though most school-age late talkers scored within the normal range on standardized language measures, they continued to show significantly weaker language skills compared to their typically developing counterparts (Rescorla, 2002, Rice et al., 2008). Large-scale epidemiological studies focused on demographic and birth variables to examine the varied outcomes on language acquisition. Sample groups included children at 16–24 months (Henrichs et al., 2011, Horwitz et al., 2003, Westerlund et al., 2006, Zubrick et al., 2007) or over 24 months (Dale, Price, Bishop, & Plomin, 2003). These studies indicated that demographic and birth variables accounted for only a modest percentage of the variance in outcomes at later stages of language acquisition.

• Toddlers with delayed expressive language: An overview of the characteristics, risk factors and language outcomes