Impaired procedural learning in language impairment: results from probabilistic categorization.

The Weather Prediction (WP) Task is a classical task of probabilistic category learning generally used for examining the dissociation of procedural and declarative memory. The current study focuses on performance of children with language impairment (LI) and compares their performance to that of typically developing (TD) children and adults with the aim of testing the procedural deficit hypothesis of LI (PDH; Ullman & Pierpont, 2005), which states that language impairment is not a specific linguistic phenomenon, but results from the dysfunction of a more general cognitive system: the procedural system. To test the generality of the procedural impairment, we needed a task that is dissimilar from language in that it does not build on sequential information. Children with language impairment show deficient learning on the Weather Prediction Task, which already appears at the early stages of the task. These results, in line with the PDH, point to the deficit of the procedural system in language impairment going beyond the language system. Whether this deficit is selective to the procedural system or is complemented by deficits in the declarative system is the subject of future studies.