Effect of typicality level on proactive inhibition in adults with mental retardation.

Adults with mental retardation heard four triads of highly typical, atypical, or unrelated words (Experiment 1, proactive inhibition buildup) and three triads of typical, atypical, or unrelated words, shifting to either typical or atypical words (Experiment 2, inhibition release). Our purpose was to examine the structure of their semantic system and determine whether they encode information in semantic memory on the dimensions of item prototypicality and list organization. No list differences occurred in Experiment 1. Apparently, interference effects inhibited encoding by organization and typicality. Amount of release varied as a function of item typicality and list organization (Experiment 2), demonstrating multidimensional encoding in semantic memory.