The inhibitory effect of long-term associative representation on working memory

Abstract

Studies on how long-term memory affects working memory (WM) have found that long-term memory can enhance WM processing. However, these studies only use item memory as the representation of long-term memory. In addition to item memory, associative memory is also an essential part of long-term memory. The associative memory and item memory involve different cognitive mechanisms and brain areas. The purpose of the present study was to investigate how associative memory affects WM processing. Before the WM task, participants were asked to store 16 pairs of dissimilar pictures into long-term memory. The participants would obtain the associative memory of these pairs of pictures in the long-term memory. The WM task was a change detection paradigm. Memory pictures in the memory array appeared in pairs (associative condition) or out of pairs (independent condition). In Experiment 1, the memory array with 6 items (3 pairs) was presented for 500 ms or 1000 ms. After a 1000 ms interval, participants needed to determine whether the probe item was the same as the memory array. The design and procedure of Experiment 2 were similar to those of Experiment 1, except that memory array was presented for only 500 ms, and 2 items (1 pairs) and 4 terms (2 pairs) were added in set size condition. Alpha power of electroencephalogram (EEG) was also collected and analyzed in Experiment 2. The results in Experiment 1 showed that WM capacity and accuracy were significantly lower in the associative condition than in the independent condition (for both presentation-time conditions: 500ms and 1000ms). The results in Experiment 2 showed that the alpha power in the independent condition increased as the memory set size increased (2 items < 4 items < 6 items), while the alpha power in the associative condition reached the asymptote when the set size was 4 (2 items < 4 items = 6 items). Both of these two experiments' results showed that WM capacity in the associative condition was lower than that in the independent condition. In conclusion, long-term associative representations inhibit the current WM processing and decrease WM capacity. This inhibitory effect is not affected by the length of encoding time. It implies that the reason for the increase of WM load by associative memory may come from the disorder of attention distribution.