Retro-cue effect (RCE) refers to the phenomenon that individuals can use retro-cues to improve their visual working memory (VWM) performance of target items after the disappearance of memory targets. To explain the mechanism of RCE in VWM, five different hypotheses have been proposed by previous studies: the hypothesis of enhancing target representations, the hypothesis of forgetting non-target representations, the hypothesis of preventing memory degradation, the hypothesis of preventing interference from probe array and the hypothesis of cognitive phase separation. Although RCE has been repeatedly observed in previous studies, the mechanism of RCE remains unclear. In this study, we conducted three experiments to test these hypotheses.
In Experiment 1, participants were asked to memorize four colors in a recall task. They needed to recall the color of the target item when the probe array presented. There are three experimental conditions, the normal cue condition, the short interval no-cue condition, and the long interval no-cue condition. In the normal cue condition, a memory array (four colored squares) presented for 200 ms. Then, the memory array disappeared for 450 ms and a retro-cue presented, followed by a 900 ms blank. Then the probe array presented. In the short interval no-cue condition and long interval no-cue condition, no retro-cue presented after the memory array, but the probe array would present after the memory array disappeared for 450 ms (short interval no-cue condition) or 1400 ms (long interval no-cue condition). The design and procedure of Experiment 2 were similar to those of Experiment 1, except we used a grey-wheel cue condition and a colored-wheel cue condition to replace the long interval no-cue condition. These two new conditions were similar to the normal cue condition, except the retro-cue would appear with a distractor of a gray wheel (grey-wheel cue condition) or with a distractor of a colored wheel (colored-wheel cue condition). The design and procedure of Experiment 3 were similar to those of Experiment 2, except a long-grey-wheel short-cue condition and a long-grey-wheel long-cue condition were used to replace the normal cue condition and colored cue condition. In the long-grey-wheel short-cue condition, the retro-cue presented for 100 ms, but the grey wheel presented for 1000 ms. In the long-grey-wheel long-cue condition, the retro-cue and grey wheel presented for 1000 ms.
The results of Experiment 1 showed that there was no significant difference in memory performance between the short interval no-cue condition and long interval no-cue condition, while the performance of the normal cue condition was better than that of short and long interval no-cue conditions. The results of Experiment 2 showed that participants obtained the RCE under the normal cue, the grey-wheel cue, and the colored-wheel cue conditions. However, the degrees of RCE obtained by these three conditions were different (normal cue > grey-wheel cue > colored-wheel cue). The results of Experiment 3 showed that participants obtained the RCE under the grey-wheel cue condition, the long-grey-wheel short-cue condition, and long-grey-wheel long-cue condition. The degree of RCE obtained by these three conditions was the same.
The results of the present study supported the hypothesis of cognitive phase separation, which suggested that the retro-cue can separate the internal attention reallocation process and decision-making process, avoiding cognitive interference from the probe display. In addition, when the retro-cue was accompanied by the distractors, the type of distractors (rather than the presentation time) affected the degree of RCE. This study provides further evidence for the hypothesis of cognitive phase separation, which is crucial to solve the debate on the mechanism of RCE and to understand the relationship between attention and VWM.