Language, aging, and inhibitory deficits: evaluation of a theory.

This article evaluates the success of Inhibitory Deficit theory in addressing two basic functions of a theory: explaining available results and predicting new findings. The review focuses on language comprehension and production, domains of cognition vulnerable to age-linked inhibitory deficits under the theory. Considerable research, however, reports remarkable age constancy in many aspects of language performance, contrary to the predictions of Inhibitory Deficit theory. For conditions that do produce age differences in language comprehension and production, evidence for inhibitory deficits is controversial at best. In predicting new findings, Inhibitory Deficit theory is constrained by lack of a well specified model, producing confusion between inhibition that occurs at a behavioral level versus a theoretical level. Modification of the theory is required to bring it in line with empirical findings on language and aging, and greater specification of underlying processes is required to reduce contradictions in predictions.