Why am I remembering this now? Predicting the occurrence of involuntary (spontaneous) episodic memories.

Involuntary episodic memories are memories of events that come to mind spontaneously, that is, with no preceding retrieval attempts. They are common in daily life and observed in a range of clinical disorders in the form of negative, intrusive recollections or flashbacks. However, little is known about their underlying mechanisms. Here we report a series of experiments in which-for the first time-the activation of involuntary memories is controlled and predicted on the basis of manipulations done at encoding. During encoding, participants were presented with pictures of scenes paired with sounds. Both scene and sound could be either unique (derived from a category that was presented only once) or repeated (derived from a category that was presented several times). During retrieval, the participants conducted an attention-demanding sound location task employing sounds from the encoding phase. In addition to the sound location task, they were asked to record all memories that might spontaneously arise during this task. Unique sounds generated most involuntary memories, consistent with the notion of cue overload. Repeated sounds rarely generated involuntary memories, but often yielded memories of repeated scenes in a voluntary (strategic) recall condition. Retrieval times were lower for involuntary than for comparable samples of strategically retrieved memories, suggesting less executive control involved in involuntary recall. Our findings show that it is possible to control the activation of involuntary episodic memories of daily scenes on the basis of well-known mechanisms of associative memory.