This project will examine who among Late Talkers are at risk for Specific Language Impairment (SLI) based on real-time measures of cognitive and lexical processing. The term Late talkers (LT) refers to infants (18-24 months) who are delayed in the onset of first words, with scores on standardized vocabulary assessment measures usually below the 10th%ile, despite normal nonverbal intelligence, hearing, development, and birth history. The critical question in LT research is how to best identify those LTs who will have Specific Language Impairment (SLI) at school age. The term SLI refers to children with normal nonverbal intelligence, but who have limitations in language, trouble communicating, difficulties with social skills, and continued language delay and academic problems throughout adolescence and adulthood. Longitudinal studies of language outcomes in LTs have had only moderate success at accurately predicting which LTs will have persistent language delay and will be classified as SLI by age 5-6. The label Late Talker is not a ?clinical? diagnostic category but simply refers to infants who have language abilities in the lower end of the normal distribution. Recent work by Dollaghan (2004, 2011) suggests that children with SLI may represent the lower end of a continuum of language abilities, and encourages future research to focus on characterizing the causal influences of these poor language abilities. Not only does the language learning environment (Hart &Risley, 1995) have a causal influence on a child?s language learning, but research shows that the individual's cognitive processing abilities (e.g., speed of processing, memory and implicit learning) also play an important role (Fernald &Marchman, in press;Graf Estes et al., 2007, Leonard et al., 2007). Therefore, using the lexical and cognitive processing deficits in SLI to inform the study of lexical and cognitive processing in infants may prove more successful in identifying LTs at greatest risk for SLI. This project will go beyond group comparisons, using a dimensional approach and fine-grained eye tracking methods to examine multiple measures of real time processing speed, novel word learning and implicit learning in the same infants. A total of 80, 18-monthold infants will participate in the project. Studies 1 - 3 will examine directly whether lexical and cognitive processing in late talking infants (N = 50) and typically developing infants (N = 30) differs for novel word learning, word segmentation, and real word recognition. Incorporating Dollaghan's proposal to examine children's language abilities from a dimensional perspective, all data will then be converted to Z-scores and individual participants'Z-scores will be rank ordered to determine whether there is a subset of infants who consistently fall on the low end of the distribution across multiple measures of speed and accuracy of lexical processing, statistical word learning (Studies 1-3) and vocabulary knowledge (Studies 4 &5). The outcomes of the current project will inform theoretical models of word learning and vocabulary development in Late Talkers by providing insights into the mechanisms that underlie individual differences in language abilities.
A late talker (LT) is a young child (generally 18-24 months old) with a delay in language onset, but with no other physical or mental disabilities who is at risk for Specific Language Impairment (SLI) by the time they reach school age. Children with SLI have significant difficulty learning and using language and often experience academic failure, have few friends in school, have poor peer relations, and have poor success in the workplace despite normal intelligence. Researchers and clinicians have not been successful in accurately predicting which LTs will have SLI. Using a newly proposed dimensional approach, this project examines the cognitive and lexical processing mechanisms that may underlie individual differences in word learning and vocabulary in infants to better identify those LTs at risk for SLI.