Working memory is a memory system of storage and encoding in a very short period of time with limited capacity. Slot model holds that individuals store a fixed number of representations generally independent of each other with fixed precision in WM. And the individual WM capacity limit is defined as the number of slots. Resource model also accepts the limitation of working memory capacity. However, it regards working memory as a pool of resource which can be flexibly assigned. Everyone will hold a small number of high-precision items or a lot of low-precision items. The number varies inversely with the resolution of stimulus.
In this research two kinds of models were examined through the regulation of some independent variables such as working memory capacity and set size of display. As the prediction of slot model, the curve of CSD (circular standard deviation, it represents the standard deviation of the circular distribution and in turn reflects the precision of the item stored in WM) will reach a stable plateau once the set size of memory display exceeds the upper limit of one's working memory. Instead, the curve of CSD will never tend to be smooth under the theoretical background of resource model. There isn't any important turning point sense of individual capacity limit. Consequently, in study 1 two kinds of models were preliminarily tested through the observation of change in the CSD curve.
The results showed that there was a significant increase of CSD from set size 1 to 6 in both two individuals groups. The slope of the CSD curve had always been significantly greater than 0. The differences of CSD in all set sizes between the two groups were always significant. While the Pm of high capacity decreased suddenly from set size 4 and the Pm of low capacity individuals declined suddenly from set size 2. The results of experiment 2 showed that there was a significant increase of CSD among set size 1，2, 3, 4, 6, 10, 16 in both two individuals groups. Additionly the slope of the CSD curve had always been greater than 0. Whereas the trends of Pm curve were same in two individual groups. Which meaned, the Pm of two capacity individuals didn't decrease suddenly from their own capacity.
Furthermore, there had different predictions based on the influence of the cue on storage precision between these two models. Besides, previous studies had found that high capacity individuals were more efficient in inhibiting the irrelevant information than low capacity individuals. Then we explored whether the cue would have different impact on the precision of two individual groups in study 2. The results showed that CSD under the valid cue condition were both significantly lower than neutral condition and the invalid cue condition in two groups. Then CSD under neutral condition were also both significantly lower than the invalid cue condition in two groups.
Previous studies of two models always used the precision of a randomly selected item to represent the precision of the whole memory display. We consider this method will conceal the variation of precision among all the items as well as the resource allocation in the whole memory display. Then we carried out study 3 to examine the precision of all the items in the memory display. The results showed that all bars were encoded to different levels of precision no matter whether 2 or 6 bars were in the display, which could be inferred from the differences of Pm and CSD. In addition, every subject had his own ranking from the mostly precise location number to the fuzziest location number, with no distinct rule.
These experimental results illustrate the following points. First of all, the processing CSD will steadily increase with the increase of set size, which suggests resource model can explain the storage of WM better. Additionly the results of study 2 further prove it. Second, the differences between the high and low capacity individual groups also include the quantity of resource, but not the ability of using cues. Third, the spatial resource allocation among all the items in the field of vision are not equal without cues, which suggests that individual distribution of resources is also very flexible in the absence of cues.