Recognition memory and the hippocampus: A test of the hippocampal contribution to recollection and familiarity

Abstract

It has been suggested that the hippocampus selectively supports recollection and that adjacent cortex in the medial temporal lobe can support familiarity. Alternatively, it has been suggested that the hippocampus supports both recollection and familiarity. We tested these suggestions by assessing the performance of patients with hippocampal lesions on recognition memory tests that differ in the extent to which recollection and familiarity contribute to the recognition decision. When targets and foils are highly similar, prior evidence suggests that, on a forced-choice test in which targets are presented together with highly similar, corresponding foils (the FC-C format), performance is supported primarily by familiarity. By contrast, when targets are presented together with foils that are similar to other targets (the FC-NC format) or when memory is tested in a yes/no (Y/N) format, performance is based much more strongly on recollection. Accordingly, a finding that hippocampal damage impaired both Y/N recognition and FC-NC recognition but spared FC-C recognition would suggest that the hippocampus selectively supports recollection. We administered Y/N, FC-C, and FC-NC tests to five memory-impaired patients with circumscribed hippocampal lesions and 14 controls. The patients were impaired on all three types of recognition test, and there was no indication that the patients were disproportionately benefited or disproportionately impaired on any test. This pattern of performance suggests that the hippocampus supports both recollection and familiarity.

Figure 1.

Test format and materials for the three kinds of recognition test. For each test, 12 images, either objects (A) or silhouettes (B), were presented at study, and memory was tested in one of three ways. For the forced-choice corresponding test (FC-C), each target (a studied item) was presented together with a highly similar foil (a new item). For the forced-choice noncorresponding test (FC-NC), each target was presented together with a foil that was highly similar to a different target from the study list. Participants were asked to point to exactly the same image they had seen during study. For the yes/no test (Y/N), the 12 targets and the 12 foils (each similar to one of the targets) were intermixed and presented one at a time. Participants were asked to respond “yes” if they had seen exactly the same image before and “no” if they had not. Asterisks identify the target items.

Figure 2.

Performance by patients with circumscribed hippocampal lesions (H) and controls (CON) on the three kinds of recognition memory tests: forced-choice corresponding (FC-C), forced-choice noncorresponding (FC-NC), and yes/no (Y/N). Discriminability was measured by d′ for the two-forced choice tests, and by d_a for the Y/N test (see Data analysis). Each participant's score is represented by a circle, and patients are identified by initials. The scores for each type of recognition test are the means of eight different tests, four constructed from objects and four constructed from silhouettes.