Exploring the nature of recency discrimination deficits in frontal lobe patients.

Abstract

Damage to the frontal lobes appears to result in a deficit in the temporal organization of memory. McAndrews and Milner (1991) recently found that subject performed tasks (SPTs) with objects allowed frontal lobe-damaged patients to circumvent this deficit and perform normally on recency judgments. The present study was an attempt to investigate the critical properties of SPTs, by comparing the performance of frontal lobe-damaged patients and healthy control subjects on recency judgments under five different encoding conditions: SPT, naming, visual imagery, visual observation, and verbal elaboration. Results revealed a significant group-by-condition interaction, indicating that patients' performance varied across encoding conditions, while controls did not. Post-hoc comparisons confirmed that patients performed significantly poorer than normal controls across all encoding tasks, except SPT. In the SPT condition, there was no significant difference between the groups. The present findings serve as a replication of McAndrews and Milner's results. Further, they help elucidate the nature of both SPTs and memory for temporal order. The fact that patients' performance in the SPT condition was superior to all other conditions, suggests that performing an action served as more than an elaborative encoding technique. It is concluded that activating and executing motor programs was the critical feature responsible for the observed SPT effect. It is further concluded that SPTs, rely on automatic processes. The use of an automatic method for item encoding may have allowed frontal lobe patients to devote available cognitive resources to encoding temporal order. Thus, SPTs compensated for frontal lobe patients' deficits in effortful processing, and hence improved their recency judgments.