Memory Subtypes in Learning Disabled Readers

This study assumes that learning disabled readers may be characterized by different patterns of memory dysfunction. To test this assumption, subgroups of LD readers were determined through a hierarchical cluster analysis, which included a memory classification battery of semantic, elaborative, and effortful encoding tasks. Eight subtypes of memory dysfunction were identified. One LD subtype, 8% of the sample, presented a normal profile; however, all subtypes were inferior to non-LD readers in composite scores reflecting elaboration and central-processing demands. Five subtypes (over 78% of the sample) demonstrated severe memory difficulties primarily with elaboration and high-effort encoding tasks when compared to the other subtypes. The results were generally consistent with memory-capacity theories suggesting that individual differences in recall are related to possessing (a) sufficient amount of structural resources (i.e., word knowledge base) to meet task demands, (b) sufficient supply of required capacity under high-effort encoding conditions, and (c) sufficient resource monitoring policy. The study provides external validation for classification of LD readers on psychometric measures according to patterns of memory performance.