The role of working memory in the occurrence of involuntary thoughts about the past and future: an experimental investigation

Previous research has demonstrated that although involuntary autobiographical memories (IAMs) and involuntary future thoughts (IFTs) occur spontaneously with minimal effort, their frequency is significantly reduced during cognitively demanding activities, which leaves their precise underlying mechanism(s) yet to be revealed. Across two experiments, we tested the hypotheses that the frequency of IAMs and IFTs may be reduced due to (1) the limited working memory capacity that enables the processing of only a finite number of thoughts and/or (2) the reduced likelihood of noticing incidental, task-irrelevant cues that may potentially trigger IAMs and IFTs. To this end, participants completed a laboratory vigilance task with irrelevant cue-words to trigger IAMs and IFTs, and random thought-probes to measure their frequency. Study 1 manipulated the level of working memory load (none, low, high) while participants performed a letter version of the N-back task during the vigilance task. The presentation of working memory task-items and incidental cue-words in the vigilance task was also manipulated (simultaneous vs. sequential). Study 2 further manipulated the type of working memory load by using either verbal or visuo-spatial N-back task while using a sequential presentation of working memory task-items and cue-words. In both studies, to further examine levels of incidental cue-noticing, participants also completed an unexpected cue-recognition task after completing the vigilance task. Cognitive load reduced cue recognition, which positively predicted IAMs frequency. While working memory type had no robust effect, IFTs tended to be more frequent under visuo-spatial load. Overall, working memory load, cue noticing, and participants’ strategic behaviours jointly shaped IAMs and IFTs retrieval. The results provide new insights about the underlying mechanisms of IAMs and IFTs in terms of their dependency on cognitive load and may open interesting avenues for future research.