UC San Diego

A substantial and still growing body of literature has consistently shown that sensitivity to the relationship between auditory and visual information plays an important role in developing language abilities (Kushnerenko et al., 2013; Soto-Faraco et al., 2012). Emerging evidence suggests that audiovisual processing may be impaired in specific language impairment (SLI) (e.g., Norrix, Plante, Vance & Boliek, 2007). The persistence of this finding in SLI over a wide age range has not yet been investigated. Importantly, typical audiovisual processing follows a protracted developmental trajectory, such that audiovisual processing abilities change with age, and do not reach full maturity until adolescence (Hillock, Powers, & Wallace, 2011; Massaro, Thompson, Barron, & Laren, 1986; McGurk & MacDonald, 1976). Furthermore, research characterizing these abilities in childhood and adolescence is relatively sparse, compared to research available in adults. Thus, the nature of audiovisual processing abilities in children is less stable and less well understood. Investigating audiovisual processing abilities in SLI in adulthood, when these abilities are more stable, may be more informative about the persistence and pervasiveness of a deficit. While research on audiovisual processing in adults is much more extensive than in children, findings span disparate fields and research paradigms and, thus, are somewhat disunified (Calvert, Spence, & Stein, 2004). In order to constrain our investigation, we looked at audiovisual processing abilities under the predictions of the intersensory redundancy hypothesis (IRH) (Bahrick & Lickliter, 2012), which makes specific predictions about how multisensory processing (i.e., audiovisual processing) affects behavior in adults. Since this particular hypothesis is relatively understudied in adults, the research in this dissertation necessarily began by investigating the predictions made by the IRH in typical adults, prior to investigating these same predictions in adults with SLI. This dissertation utilized eye-tracking and behavioral measures to investigate intersensory processing in adults with and without SLI. Chapter 1 provides an overview of the research motivating the questions addressed in this dissertation. Chapters 2-4 present the studies included in this dissertation. Specifically, in Chapter 2, in a group of typical adults (N = 30) accuracy and reaction time in a go/no-go task were compared in audiovisual, auditory-only, and visual-only conditions. In Chapter 3, in a group of typical adults (N = 30) accuracy, reaction time and looking behavior were compared in a go/no-go task, in synchronous and asynchronous audiovisual conditions, in three different experiments, in which timing, predictive cue value, and signal quality were manipulated. In Chapter 4, normal language adults (N = 12) and adults with SLI (N = 12) were compared on accuracy, reaction time, and looking behavior in a go/no-go task, in three different experiments, which looked at performance in an audiovisual condition versus performance in several comparison conditions. Finally, Chapter 5 discusses the implications the current findings for future research in typical and language disordered populations and for clinical practice