Implicit Learning in Preschoolers with and Without Developmental Language Disorder

The purpose of this study was to compare implicit learning of sound categories across preschoolers with and without developmental language disorder (DLD), in order to test the Procedural Deficit Hypothesis (Lum, Conti-Ramsden, Page, & Ullman, 2012), which argues that procedural memory, the basis for implicit learning, is the core deficit in DLD. We tested 52 preschoolers in total, 26 with typical language development (TLD), and 26 with DLD. Preschoolers participated in a computer-based task assessing implicit mapping of sounds to meanings. We predicted that children with DLD would show deficits in implicit learning relative to children with TLD. Results were congruent with our hypothesis, however, an unforeseen experimental-design issue changed our interpretation of learning effects. During the mapping task, the target picture switched sides between experimental trials (vs. repeating on the same side) roughly 65% of the time. Participants noticed the tendency for visual targets to alternate, relying on this pattern to predict where the target would appear. This represents a form of implicit learning--just not the one we intended to probe. Both groups of children showed sensitivity to the alternation pattern, but only TLD children reached above-chance accuracy using the strategy. We discuss implications of this result for the Procedural Deficit Hypothesis and discuss follow-ups to this study, currently in progress