The Trade-off Relationship Between Number And Precision In Visual Working Memory

Visual working memory(VWM) is one of the most prominent mechanisms in human information processing system. Individual differences of VWM can be embodied in the two aspects, VWM number and VWM precision. There are three basic models for the storage mechanism of visual working memory storage: classic slot model, "slot + average" model and flexible resource model. The key point for distinguishing these models is to confirm whether there is an inverse relationship for the trade-off between VWM number and VWM precision. But the question for the trade-off between VWM number and VWM precision is still remain unclear. Here, the author adopted the color feature as visual material, and tested the trade-off relationship between VWM number and VWM precision by recording the event-related potentials(ERP) during the retention interval of a change detection task and by conducting behavioral experiments with a mixture model fitting. The author used these techniques to confirm the relationship between VWM number and VWM precision, to give the previous related researches systematic discussions and to explore the reasons for the unclear results.This study is composed of three parts. The first part investigates the relation between VWM number and VWM precision for color feature by recording the event-related potentials in a change detection task. But the author did not observe the evidences that show an inverse relationship for the trade-off between VWM number and VWM precision. In the second part, the author divided the participants into high VWM capacity group and low VWM capacity group, by using an color recall task and the mixture model analysis to separately assess the probability and the precision of the memory item, the author tested whether the relationship between VWM number and VWM precision affected by the VWM capacity in different condition of precision demand, the results show that the reason why author could not observe the trade-off between VWM number and VWM precision in the first part is that the participants could not allocate the memory slots flexibly according to the task requirements. In the third part, after the author discussed the reasons why the author could not obtain the trade-off between VWM number and VWM precision in the first two parts, the author found an inverse relationship for the trade-off between VWM number and VWM precision in the high VWM capacity group during long exposure duration. These results reject the classic slot model, and provide the new evidences for the "slot + average" model. In addition, the results show the reason why the previous research could not find the trade-off between VWM number and VWM precision is that participants could not allocate the memory slot by the top-down control. The results also show that the exposure duration and VWM capacity will determine the mode of memory slot allocation. Finally, the author put forward a two-phase resource allocation hypothesis to reconcile the argument about the slot allocation modes.