The Effects of Activation Levels of Visual Long-Term Memory on Visual Short-Term Memory

Abstract

It is a fundamental question that whether visual short-term memory(VSTM) and visual long-term memory(VLTM) are two separate stores or two different states of the same representation. Previous researches focused on whether VSTM could be facilitated by VLTM, however, existing studies on this topic yielded conflicting results. Most neurophysiological or behavioral studies adopted faces as stimuli, and have arrived at the conclusion that VLTM could facilitate VSTM. It ought to be noted that in studies that found no facilitation, the exposure of the experimental materials was not sufficiently to activate VLTM. Therefore, it was hypothesized that only a highly activated VLTM could facilitate VSTM.The purpose of the present study was to investigate the effect of activation level of VLTM on facilitating VSTM within the change-detection paradigm. In Experiment 1, participants were instructed to memorize a study image including 6 geometric figures(6 random shape-color bindings from a pool of eight shapes and eight colors), and then after a random inter-stimulus interval(1, 1.5, or 3 s), either the same image or an image with one shape or color changed was presented, and participants were asked to judge whether they detected a change. In Experiment 2, a total of 8 geometric figures with fixed combinations of color and shape were used to substitute all the random combinations of experiment 1. The experimental procedure and design was identical to experiment 1. One hour after the experiment, participants were asked to participate in a post-experiment to examine whether the study stimuli were stored in VLTM. In Experiment 3, participants were asked to visually study the 8 figures in experiment 2 for a week(at least 10 min a day). Then, they took part in a pre-experiment(the same as the post-experiment in experiment 2) to test whether a highly activated VLTM was obtained. At last, the experimental procedure as described in Experiment 2 was performed. The results showed that although VLTM was formed in experiment 2, there was no significant increase in d' or K value of VSTM, indicating no facilitation of VLTM in this case. However, in experiment 3, VLTM was highly activated, and a better performance was observed as compared with experiment 1 and 2. In addition, the effect size of ISI decreased as the activation level of VLTM increased from experiment 1 to experiment 3. The results suggest that whether VLTM can facilitate VSTM is mainly depend on the activation level of VLTM, only a highly activated VLTM can facilitate VSTM, and can inhibit the rapid fading of VSTM traces. On this basis, we conclude that VSTM and VLTM are more likely to be two states of the same representation.