The Retention And Neural Correlates Of Long-term Memory Of Novel Words

Learning and memory is the focus of cognitive research.The previous studies on the word learning mainly accessed the memory of novel words within a short time interval instead of a long-term effect.Some studies found that whether the novel words were acquired implicitly or explicitly was an important factor affecting the long-term retention of novel words.In addition,repeated retrieval is also an important factor to promote long-term memory.However,previous studies focused on the effect of retrieval practice and its interval on memory in a short-time scale.Fast Mapping(FM)is an implicit learning paradigm that learners obtain word meaning by inference,which has received widespread attention recently.A recent study revealed that the words acquired under Fast Mapping have more stable long-term memory representations than Explicit Encoding(EE).Therefore,the present study examined the effects of learning conditions(FM vs.EE),as well as retrieval practice intervals,on the long-term retention of novel words.In addition,the neural mechanism of memory has also been widely concerned recently.Researchers have found that the neural similarity between learning items during encoding may be an important factor on memory.Thus,the neural correlates of long-term memory of novel words are also explored in the present study.This study consisted of three experiments.Experiment 1 examined the effect of learning manners on the long-term retention of novel words.A 3(Learning condition: EE,FM,FM-d)× 4(Learn-test interval: 10-min,2-day,17-day,1.5-year)within subject design was used in experiment 1a(The subjects were all college students.N=19),the third test was occurred 51 days after initial learning in experiment 1b(N=18),to explore the influence of different leaning manners and interval on novel words retention.A 2(Learning condition: EE,FM)×2(Retrieval practice: yes,not)between subject design was used in experiment 2(N=149)to explore the influence of retrieval practice on long-term retention in different learning manners.Through Explicit Encoding paradigm,we compared the neural pattern similarity as well as ERP between remembered and forgotten items in the learning phase to explore the mechanism of memory in experiment 3.Meanwhile,the resting sate EEG signal was recorded to investigate the relation between alpha oscillation and memory performance.The results of experiment 1 showed that the retention of words learned under explicit encoding tended to decline over time,but the recognition of fast mapping condition showed a unique advantage in long-term retention: stable retention of memory even over a time interval as long as one and a half years.However,whether the novel objects and familiar objects simultaneously presented in Fast Mapping paradigm were from the same or different categories did not affect the memory retention of novel words.We investigated the effect of retrieval practice on long-term memory retention with different learning manners in experiment 2.The results showed that the memory performance of words learned from Fast Mapping increased after six months with retrieval practice,while the memory performance of Explicit Encoding remained stable.Without the retrieval practice,the performance in Fast Mapping condition remained stable but that in Explicit Encoding condition declined.The results of Experiment 2 verified the advantages of Fast Mapping learning in long-term retention.At the same time,retrieval practice promoted both learning manners in memory retention,but the Explicit Encoding learning benefits more from retrieval practice.Experiment 3 used Explicit Encoding paradigm combined with EEG to explore the neural mechanism of memory.It was found that the the neural pattern similarity of encoding remembered items was greater than that of forgotten items in the relative early coding stage,and the opposite pattern was observed in the relative late coding stage.The subsequent memory effect on LPC(800-140ms)not only be measured in the shorter interval,but also reflected the memory performance after 1 month.In addition,there was a negative correlation between the power of alpha oscillation in the 5-min resting phase and the subsequent memory performance,which might reflect the increased information processing and benefit memory retention,but failed to predict the memory in the longer time scale.In brief,the present study showed that the incidental Fast Mapping learning have an unique advantage in long-term retention comparing with the Explicit Encoding.Retrieval practice promoted both learning manners in retention,but the Explicit Encoding benefits more from retrieval practice.The brain activity in the encoding and resting phase could predict the subsequent memory.