? Audiovisual processing in developmental language disorder Emerging developmental studies show that visual speech cues facilitate the acquisition of important building blocks of language, such as phonemes and words, and shape the development of both speech production and speech perception. Because visual speech cues influence multiple aspects of typical language acquisition, and speech perception more generally, we ask whether impairment in the processing of visual articulatory movements and/or difficulty in integrating such movements with concurrent auditory speech may underlie some of the deficits observed in children with developmental language disorder (DLD). DLD is characterized by difficulties in acquiring language in the absence of an easily identifiable cause, such as hearing impairment, frank neurological disorders, or low non-verbal intelligence. It affects approximately 7% of preschool children in the US and is typically a life-long condition. Earlier studies suggest that at least some aspects of audiovisual processing are impaired in DLD, but the causes remain unknown. In this project, we propose to examine in children with DLD and their typically developing (TD) peers a set of mechanisms that are essential for normal audiovisual processing. These mechanisms include the following: (1) sensitivity to temporal relationships between events in auditory and visual modalities; (2) sensory encoding of speech-relevant visual features, namely shape and motion; (3) allocation of attention to features of complex visual objects; and (4) knowledge of auditory/articulatory correspondences for speech sounds. Examining these mechanisms in the same groups of children with DLD and TD will provide information about both the hetero/homogeneity of audiovisual impairments in DLD and the effects of impairment in just one vs. several mechanisms on audiovisual language use. We combine behavioral measures with ERP and EEG data analyses in order to map the nature of neural processes engaged by each mechanism. Understanding the causes of audiovisual processing difficulties in DLD has significant clinical implications. Audiovisual integration normally facilitates some of the linguistic skills that are impaired in DLD, such as phonological and lexical processing and speech-in-noise perception. Hence, identifying the mechanisms that prevent children with DLD from using visual speech cues as well as their TD peers do and rehabilitating them could potentially lead to improvements in these linguistic skills. Additionally, comparing the neural processes underlying audiovisual integration in children with typical and atypical language ability provides a unique window into the development of the neural networks connecting auditory and visual modalities and their impact on normal and disordered language function.
Developmental language disorder (DLD) affects at least as many children as autism and stuttering combined and has a life-long impact on individuals' well-being. Language acquisition is a multisensory process, in which seeing a talker helps children learn speech sounds and words of their language. Our earlier studies showed that the ability to combine information from audition and vision is impaired in children with DLD. The goal of this research is to identify specific neural mechanisms responsible for this impairment and help determine whether these DLD children's language acquisition and speech perception difficulties may be alleviated by therapy techniques that focus on enhancing audiovisual processing skills.
