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The Journal of Neuroscience, November 2, 2005, 25(44):10138-10146; doi:10.1523/JNEUROSCI.2731-05.2005
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Behavioral/Systems/Cognitive
Declarative Memory, Awareness, and Transitive Inference
Christine Smith1 andLarry R. Squire2,3 1Institute for Neural Computation and 2Departments of Psychiatry, Neurosciences, and Psychology, University of California, San Diego, La Jolla, California 92093, and 3Veterans Affairs Medical Center, San Diego, California 92161
A characteristic usually attributed to declarative memory is that what is learned is accessible to awareness. Recently, the relationship between awareness and declarative (hippocampus-dependent) memory has been questioned on the basis of findings from transitive inference tasks. In transitive inference, participants are first trained on overlapping pairs of items (e.g., A+B-, B+C-, C+D-, and D+E-, where + and - indicate correct and incorrect choices). Later, participants who choose B over D when presented with the novel pair BD are said to demonstrate transitive inference. The ability to exhibit transitive inference is thought to depend on the fact that participants have represented the stimulus elements hierarchically (i.e., A>B>C>D>E). We found that performance on five-item and six-item transitive inference tasks was closely related to awareness of the hierarchical relationship among the elements of the training pairs. Participants who were aware of the hierarchy performed near 100% correct on all tests of transitivity, but participants who were unaware of the hierarchy performed poorly (e.g., on transitive pair BD in the five-item problem; on transitive pairs BD, BE, and CE in the six-item problem). When the five-item task was administered to memory-impaired patients with damage thought to be limited to the hippocampal region, the patients were impaired at learning the training pairs. All patients were unaware of the hierarchy and, like unaware controls, performed poorly on the BD pair. The findings indicate that awareness is critical for robust performance on tests of transitive inference and support the view that awareness of what is learned is a fundamental characteristic of declarative memory.
Key words: awareness; transitive inference; amnesia; memory; declarative; hippocampus; medial temporal lobe
Received July 1, 2005; revised September 13, 2005; accepted September 19, 2005.
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