Cognitive mechanisms underlying the formation of offline representations in visual working memory
Abstract: Visual working memory (VWM) plays a foundational role in advanced cognitive functions. The state-based modelspropose a hierarchical organization of functional states, where memory representations with high attentional priority are retained in anonlinestate(i.e., active state),while those with lowerpriority are keptinanoffline state (i.e., passive state) for later use. The memory representations can be dynamically transferred between the two states according to thetask demands. However, there was rare work to explorehow the memory representations transitionedinto the offline state from the online, generating the offline representations. Here,we put forward two hypothesis, the consolidation hypothesis and the fade-awayhypothesis.To explore this question, participants were instructed to remember two sequential memory arrays, with Memory array 2 being detected before Memory array 1. In this memory task, Memory array 1 was held in the offline state during the active maintenance of Memory array 2. Colored squares servedas memory stimuli. 30 healthy college students participatedin each experiment. We primarily modulated the temporal context related to the state transformationof memory representations: the interval delay between the two memory arrays in Experiment 1 and the presentation time of Memory array 2 in Experiment 2. The load of online memory varied betweentwoandfour in each trial. These variables were within-subject factors. Experiment 1 aimed to verify that the shortage of interval delay between memory arrays led to the failure of state transformation in the condition of 0.8s-interval. Experiment 2 attempted to determine which hypothesis, consolidation or fade-away, aligned better with the state transformation process.The exploration of representational state transformation was builton the resources-dissociation account, which proposed that the offlinerepresentations areindependent ofthe activeprocessing of onlinerepresentations.Memory arrays 1 and 2 were used to test the offline and online memory, respectively.The results of Experiment 1 showed thatvariations in online load did not affect offline memorywhenextending the interval delay from 0.8s to 1s. This indicatedthatthestate transformation of Memory array 1 continued beyond 0.8s afterits disappearanceand could completewithin a1s-interval. In Experiment 2, the interval was designed at 0.8s. We observedthat the online load variation had no impact on offline memory when extending the presentation time of Memory array2 from 0.2s to 0.5s. This supported the consolidation hypothesis, indicating that the sufficient presentation time of Memory array 2 allowed forthe state transformation of Memory array 1 tocompletebefore the subsequent processing of Memory array 2. Thus, we concluded that the state transformation involved a consolidation processing to transfer the online representations to the offline state, rather than natural fade-away of persistent neural activity.In summary, the state transformation actsas a process of consolidating online memory representations into the offline state,thereby formingoffline representations. Thisprocesscan be completed within a sufficiently long retention interval, or continue during the presentation of subsequent stimuli when providing a deficient interval.The current findingsprovidefresh insights intothe mechanisms of representational maintenance in the two distinct states.