Symbolic Performances in Learners with Developmental Disabilities

Krista Wilkinson

Fundamental to human intellectual functioning is the ability to form categories made up of multiple members. Many individuals with mental retardation have trouble with categorization in general and, oftentimes, in using linguistic symbols (words) as a means for organizing or structuring those categories. Yet efforts to study category formation has been hampered by two problems; (1) lack of a concise definition of the concepts of symbol and category, and (2) limitations in available methodologies. This project represents an explicit integration of state-of-the-art approaches derived from stimulus control, psycholinguistics, and electrophysiological recording that is intended to address both of these problems.

We have successfully initiated behavioral and biobehavioral methods for exploring category formation. A well-established behavior analytic approach for establishing and verifying "equivalence classes" has been integrated with pycholinguistic and electrophysiological methods by which semantic language categories have historically been studied. The methods were developed and tested with non-clinical adults during the first year, and are in the process of being adapted for individuals with intellectual impairments. In this time, we have evaluated whether laboratory-generated equivalence classes provide an appropriate model for the study of semantic categories. This has been accomplished two ways: (1) comparison of electrophysiological testing of brain responses to equivalence classes with brain responses elicited by semantic language categories, and (2) evaluation of whether equivalence classes adhere to the same structural constraints observed in many semantic language categories. Results to date suggest that laboratory-generated equivalence classes elicit the same brain responses as semantic language categories, and can adhere to the same structural constraints as semantic categories. These results support the use of equivalence categories as experimental models of category formation. In the current year, this project will be dedicated to replicating the early findings within the population of individuals with intellectual disabilities. Research has been initiated with the first 10 individuals with severe mental retardation.