The long and the short of it: relational memory impairments in amnesia, even at short lags

Abstract

Classic studies of amnesia led to characterizations of hippocampal function emphasizing involvement in long-term memory rather than short-term (or working) memory. In two experiments, we show that when memory for relations among co-occurring items is tested, hippocampal amnesia results in a deficit even at very short lags. Hence, we find evidence for hippocampal involvement in relational memory, even at short lags normally considered the province of working memory.

Figure 1.

Magnetic resonance scans of hippocampal amnesic patient 0001. The images are coronal (left) and transverse (right) slices through the midportion of the hippocampus. They are from four sets of high-resolution T1-weighted (magnetization prepared rapid gradient echo) scans that have been averaged together to optimize gray-white contrast. Volume changes can be noted in the region of the hippocampus bilaterally.

Figure 2.

Stimuli used to test relational memory. Top, In experiment 1, repeated (match) versus manipulated (nonmatch) versions of previously viewed scenes probed memory for the relations among scene elements, at short (lag 1), medium (lag 5), or long (lag 9) lags. Bottom, In experiment 2, three-face test displays superimposed on previously viewed scenes probed memory for face-scene relations, at either short (lag 1) or long (lag 9) lags. Red boxes are for illustrative purposes only.

Figure 3.

Deficit in relational memory in amnesia. The proportion of correct relational memory judgments for the comparison group (white bars) and the amnesic patients (gray bars) in experiment 1 (top) and experiment 2 (bottom) are shown. SE bars are plotted around the means. The dashed line represents chance performance.