Forgetting is an important phenomenon in working memory. Understanding forgetting could offer a window into the very core of cognition. According to the removal hypothesis, forgetting occurs because distractors interfere with memory traces, and this interference can be actively removed. In the decay refresh hypothesis, forgetting occurs because the memory trace decays with time and can be recovered by refreshment. In the present study, a multidistractor complex span task was designed to directly test the cause of forgetting. The free time after a particular distractor and the total free time were manipulated, with the priming effect of the repeated distractor as a detector. The results showed that a longer free time after the first distractor weakened the priming effect, but a longer total free time had no influence. These results supported the removal hypothesis. The forgetting of distractors was not due to decay but due to removal. The trace of a distractor would be removed when it stops being processed. The removal of a distractor occurs when individuals have free time directly after it, whereas the free time after another distractor is not beneficial.
Keywords: Working memory; decay; forgetting; removal.