Individual Differences & Clinical Populations
Much research on speech perception and word recognition focuses on “normal” individuals - people who hear well, and have normal language abilities. Such research has revealed a great deal about the general characteristics of speech processing. From the perspective of this group of listeners, speech appears to be processed effortlessly and accurately, despite the challenging nature of the problem. In reality, though, there is a wide range of variation in how individuals use language and how well they do it. A wealth of work in the fields of speech pathology and communication disorders has documented how differences in cognitive, sensory or social factors during development or later in life affect language performance or how well people use language. The MACLab is interested in how these differences affect language processing, that is the process by which listeners unpack meaning from the speech signal. While work in speech pathology typically focuses on understanding a single population or disorder (e.g., people with autism, individuals who use Cochlear Implants), in the MACLab, we examine multiple forms of individual differencesas a way to understand the different dimensions along which the language processing system varies.
Currently we are investigating two somewhat complementary populations: adolescents with language impairment (LI) and people who use Cochlear Implant (CIs). LI is diagnosed when an individual (usually a child) scores poorly in generalized measures of language in the absesnce of any other causal factor such as hearing difficulties, speech production problems, or neurological or developmental disorder. These people have very clear deficits in higher level language (e.g. grammar), but there is also some evidence that they may have a perceptual deficit as well. Cochlear Implants are an increasingly common approach to remediating severe hearing impairment, in which a small computer processes incoming sound and electrically stimulates the cochlear to help a person hear. This group can offer an interesting complement to people with LI as those who lost their hearing late in life will generally have good higher level language, but much poorer perceptual skills.
Our findings indicate that even when individuals from these populations perceive words correctly, the process by which they reach the correct interpretation differs. Adolescents with SLI have difficulty maintaining activation for the word they are hearing, while individuals with cochlear implants are delayed in activation and show an adaptive hedge-your-bets strategy, committing less strongly to the target interpretation and sustaining activation of competitor words, in case they have to revise their initial interpretations. We hope that by identifying differences in how different special populations understand language, we can improve diagnostic and intervention strategies and at the same time better understand “normal“ language processing and development.
McMurray, B., Samelson, V., Lee, S., and Tomblin, J.B. (2010) Individual differences in online spoken word recognition: Implications for SLI. Cognitive Psychology, 60(1), 1-39.