The Mechanism Of Working Memory Retrieval With N-BACK Paridigm

N-BACK task as a classic Working Memory(WM)paradigm was often used to study the WM capacity under different workloads.Although the investigations WM were huge,however,most of studies about WM was focused on understanding how WM process input information,but rarely on how WM retrieval processed information.For that,multiple experiments were designed in order to study the subject.Experiment 1 was used a 2(memory retrieval: recollection vs.familiarity)× 3(memory load: 1 vs.2 vs.3)mixed designed experiment combine with Event Related Potential(ERP)technique to investigate how to retrieval semantic information with WM process.To enable participants retrieval stored item with recollection-based recognition,recollection-based N-BACK task had only one test stimulus presented on center of the monitor,participants had to determine whether test stimulus matched to the target N-BACK presentation prior to the test stage;To enable participants retrieval stored item with familiarity-based recognition,familiarity-based N-BACK task had two test stimuli presented on left and right side of the monitor simultaneously,participants had to determine which of stimuli was matched to the target N-BACK presentation prior to the test stage.0-BACK trails were as baseline condition to current study.As results,there were N1/P1/N2/P3a/FN400 been found on frontalcentrol electrodes and a large amount of LPC was found on parietal electrodes.With observation of 0-BACK trails,it had only N1/P1/N2 components,and with analysis of N1/P1/N2 from N-BACK trails,found that these components could easily affected by physical differences of test stages,indicating that these components cannot reflect process of memory retrieval.Analysis of LPC and P3 a showed that: the amplitude of LPC was greater in familiarity-based N-BACK than recollection-based N-BACK,however,the amplitude of LPC could decreased with increase of memory load,indicated the LPC amplitude differences of familiarity-based and recollection-based N-BACK may cause by the process difficulty that process of familiarity was easier than recollection;The amplitude of P3 a was increased with increase of memory load,and the latency of familiarity-based N-BACK was earlier that recollection-based NBACK.Results of FN400 showed that memory load could not cause differences,but importantly,FN400 amplitude from familiarity-based N-BACK was greater than recollection-based N-BACK,and its latency was also earlier,indicated that FN400 was reflected to process of memory retrieval.Experiment 2 was a 3(stimuli type: new vs.old vs.similar)× 3(memory load: 1vs.2 vs.3)mixed design total within subject study.Previous episodic memory(EM)retrieval study suggested that dissociation of recollection and familiarity could investigated by comparing ERPs from recognize “old” or “new” or “similar” stimuli,however,WM retrieval study could use same method as EM retrieval study or not was unknown.Therefore,the procedure of experiment 2 was same as recollection procedure of experiment 1,but had “old”,“new”,and “similar” types of test stimuli.The analysis of experiment 2 showed that there was nothing differences between different types of test stimuli(both amplitude and time-frequency analysis),indicated that test stimuli type could not cause different retrieval process in WM,and study of WM retrieval cannot use same method as EM retrieval.WM could process semantic and spacial information separately in different sub-system.The retrieval of semantic information was investigated with experiment 1,however,this cannot further find the retrieval of spacial information.Experiment 3 was used a 2(memory retrieval: recollection vs.familiarity)× 3(memory load: 1 vs.2 vs.3)mixed designed experiment with spacial stimuli.As a result of experiment 3,FN400 differences by retrieval method was mainly on F4 and FC4 electrodes,this was same as found of previous studies which special information was mainly processed on right hemisphere.There was also a result showed that there were no FN400 differences between 2-and 3-BACK conditions,however,they both were significantly lower than FN400 from 1-BACK condition.This may indicate that participants were more preferring to use familiarity to retrieval 1-BACK condition information.The result of LPC was similar to the experiment 1.In brief,current study found that the retrieval of WM under N-BACK paradigm could not affected by different test stimuli type(new/old/similar),and only FN400 was correlated with retrieval of WM under N-BACK paradigm,and it was more sensitive to familiaritybased retrieval.LPC was more related with processing difficulty factors,but not retrieval methods.