Impaired relational organization of propositions, but intact transitive inference, in aging: Implications for understanding underlying neural integrity

The ability to perform relational proposition-based reasoning was assessed in younger and older adults using the transitive inference task in which subjects learned a series of premise pairs (A > B, B > C, C > D, D > E, E > F) and were asked to make inference judgments (B?D, B?E, C?E). Learning of premise pairs was related to subsequent inference performance and conscious awareness of the stimulus hierarchy (A > B > C > D > E > F). Despite extended training, age-related deficits were observed for response times, accurate learning of the premise pairs, making inference judgments, and articulating the hierarchy. When performance for younger and older adults was examined with respect to whether they were subsequently considered aware of the hierarchy, older and younger adults still significantly differed on their accuracy for studied premise pairs, but performance between the age groups was similar for the inference pairs. Successful transitive inference performance is contingent upon the relational organization of propositions within memory and such processes are impaired in aging, potentially leading to disruptions in conscious access to the stimulus hierarchy. Such findings, in concert with previous neuropsychological and neuroimaging studies, implicate an age-related deficit in the functioning of frontal and medial temporal lobe structures, with particular emphasis on the hippocampus.