The Neural Mechanisms Of Inhibition In Directed Forgetting

Directed forgetting refers to the intentional and directional of forgetting, which is one of the important components of memory systems. It is of great significance on the humanity’s healthy to forgetting the outdated information or painful experience. Great achievements have been made in the research on directed forgetting since the directed forgetting paradigm was developed by Bjork. The TBF items was showed worse performance than the TBR items, this is referred to the directed forgetting effect. By far, there were no consensus theory to explain the internal mechanisms of directed forgetting effect, and there are two kinds of theories accounts for it, differential rehearsal account and inhibitory account. The two accounts were all supported by some studies of themselves. However, the inhibition account was still in argument. Retrieval inhibition was generally considered playing an important role in the list-method directed forgetting paradigm. While in the item-method directed forgetting paradigm, no effective evidence to support the inhibition theory, and it is not clear which pattern of inhibitory mechanism worked. In order to investigate the inhibitory mechanism in the directed forgetting, and solve the theoretical dispute, we adopt event-related brain potentials (ERP) method to investigate the cognitive mechanism of directed forgetting.The present research was focus on the ERPs provoked by study phase and test phase in the item-method directed forgetting paradigm respectively. If directed forgetting was an active inhibition process, forgetting different amount of information need different amount of cognitive resource. In other words, a load effect on directed forgetting was expected. So in Experiment1, we examined whether the load effect on directed forgetting was turn out. We adapt the item-method directed forgetting paradigm. We utilized a single trail memory test. Specifically, different load of memory items were presented to the subjects, and a remembering/forgetting cue was followed indicating these items were to-be-remembered/to-be-forgotten. Then we examined the ERPs evoked by the remembering/forgetting cues of different load. The load effect on forgetting cue was expected, that is, the ERPs evoked by the forgetting cue in high load condition was different than that in the low load condition. In the previous studies of directed forgetting, the TBR items and TBF items were compared directly without the control group which the items was not associated with a remembering cue or a forgetting cue. So it is hard to testify that the forgetting was due to the inhibition mechanism. In the Experiment2, we added the control condition into the item-method directed forgetting paradigm. That is, no remembering/forgetting cues were presented followed by the studied items. Record the ERPs evoked by the items presented in the test phase. And compared the old/new effect elicited by the three kinds of studied items (TBR、TBF、C).Through the brief analysis of experimental results, we have obtained the following conclusions,(1). We observed the load effect on directed forgetting. In the forgetting condition, a positive deflection was found for high load cue than for low load cue during the230-330ms time window. It suggests that greater cognitive resources were involved in processing TBF information. This result implicates that forgetting is an active process involving inhibition.(2). The pattern of the old/new effect among the three conditions was different from each other. Specifically, during the300-400ms time window, C items elicited a frontal old/new effect, and the TBR items elicited a parietal old/new effect. However, the old/new effect for TBF items was presented during the400-500ms time window and reached its maximum over the right central scalps. And the old/new effect elicited by TBR items and C items were presented over the left-central scalps. It might suggest that the TBF items were inhibited, and subjects were more familiar with the TBR items and C items. During the500-800ms time window, the old/new effect elicited by TBR items was presented almost over the whole scalps. The TBF items elicited a frontal and central old/new effect. The C items elicited a frontal old/new effect. We suggested that the intensity of recollection was different across the TBR items, TBF items and C items. TBR items and TBF items were rehearsed in the different extents, and C items were not rehearsed. These results suggested that the directed forgetting was result of the differential rehearsal together with the inhibition.