| The work reported here was directed at illuminating the brain systems mediating memory for relations and the time-course of the critical processes. Eye movements and event-related potentials (ERPs) were used to examine the time-course of subjects' access to and use of relational memory. In three eye-movement experiments, subjects studied face-scene pairs and were tested with 3-face displays superimposed on the scenes viewed earlier. When, at test, there was a preview of the scene before each 3-face display, disproportionate viewing of the matching face, from among the other, equally familiar faces was evident just 500-750 msec after the faces were presented. This effect was similar in magnitude and time-course whether or not behavioral responses were required. The effect was delayed approximately one second if the preview was not provided. In the ERP experiment, relational memory effects were evident beginning as early as 270-350 msec after face onset, early enough in time that it might be part of the chain of events leading to the preferential viewing observed in the eye-movement experiments. Relational memory effects were also observed on two other ERP components: the late positive complex (LPC), with a latency of 600-900 msec, which had been the earliest documented component sensitive to relational memory, and also the N400, which reflected some combination of item and relational memory.; Another set of experiments explored the role of the hippocampus in supporting relational memory. In three experiments conducted with well-characterized amnesic patients, disproportionate impairments were seen in memory for the relations among items in scenes, as compared to memory for the scenes themselves and memory for a single critical object embedded in those scenes. Patients with confirmed bilateral hippocampal damage were impaired in memory for relations among co-occurring items, with performance not better than chance at longer lags. More surprisingly, memory impairments were also evident even at the shortest possible lags (lag 1) when there were no intervening stimuli between corresponding study and test trials.; Taken together, these findings indicate that relational memory processes occur early and spontaneously, and are critically dependent upon the hippocampus, consistent with and extending the relational memory theory. |
