Memory for items and relationships among items embedded in realistic scenes: disproportionate relational memory impairments in amnesia

Abstract

Objective: The objective of this study was to examine the dependence of item memory and relational memory on medial temporal lobe (MTL) structures. Patients with amnesia, who either had extensive MTL damage or damage that was relatively restricted to the hippocampus, were tested, as was a matched comparison group. Disproportionate relational memory impairments were predicted for both patient groups, and those with extensive MTL damage were also expected to have impaired item memory.

Method: Participants studied scenes, and were tested with interleaved 2-alternative forced-choice probe trials. Probe trials were either presented immediately after the corresponding study trial (Lag 1), 5 trials later (Lag 5), or 9 trials later (Lag 9) and consisted of the studied scene along with a manipulated version of that scene in which 1 item was replaced with a different exemplar (item memory test) or was moved to a new location (relational memory test). Participants were to identify the exact match of the studied scene.

Results: As predicted, patients were disproportionately impaired on the test of relational memory. Item memory performance was marginally poorer among patients with extensive MTL damage, but both groups were impaired relative to matched comparison participants. Impaired performance was evident at all lags, including the shortest possible lag (Lag 1).

Conclusions: The results are consistent with the proposed role of the hippocampus in relational memory binding and representation, even at short delays, and suggest that the hippocampus may also contribute to successful item memory when items are embedded in complex scenes.