I have just read a short article by Bradley, Moulin and Kvavilashvili in the March 2013 edition of The Psychologist, the BPS offical publication called Involuntary autobiographical memories.
Involuntary autobiographical memories (IAMs), pop into our minds without any deliberate attempt at retrieving them. They have been proposed as the result of ecphory, an automatic memory process where events, words or objects in the environment match stored information and bring a related memory into consciousness without any ‘request’ for its retrieval. Although they are very common and normal, they can be troublesome in PTSD flashbacks, epilepsy and under some drugs.
The IAMs that people notice and make note of seem to occur when they are not concentrating on a task but instead doing something like walking or eating. But with other methodology they can occur more often. One method is to record subjects as they generate continuous free word associations for half a minute and then play them the tape and have them report any autobiographical memories that had come to mind during the chain of associations. About 90% had IAMs. So they are probably much more common than we notice.
“IAMs are more likely to be of a specific event, and come to mind significantly faster than voluntary autobiographical memories. They are also more likely to result in bodily reactions and impact on current mood than voluntary memories. However, no differences were observed in terms of perspective experienced in memory (field vs. observer) and the accuracy (measured by participants’ own confidence ratings) of recorded memories.”
“According to Conway and Pleydell- Pearce’s influential model of autobiographical memory, during involuntary recall ‘ecphoric’ cues can bypass the usual top-down strategic retrieval pathway, involving activation of the left frontal lobe, resulting in a rapid formation of memory.”
When Penfield stimulated the temporal lobe - “The resulting phenomena included sights, sounds and emotions of past events, which the patients recognised spontaneously as personal experiences, and noted that their ‘vividness or wealth of detail and the sense of immediacy that goes with them serves to set them apart from the ordinary process of recollection’ .”
“Hall carried out a PET study in healthy controls, using emotionally charged pictorial cues, and found that involuntary memory retrieval by-passed the initial search process, mediated by the prefrontal cortex, which occurs in conscious voluntary retrieval. This concurs with Conway … that involuntary retrieval can bypass the pathway involving activation of the left prefrontal lobe. ”
“Because of the automatic nature of retrieval, involuntary memories may not require any working memory input. ”
The authors of this article and their sources appear to treat IAMs as common but not that common and fairly vivid. These are the ones people are aware of, anyway. But I am inclined to think that this automatic presentation of memories is going on much of the time. And much of it would not be surprising or noteworthy . Computers have procedures to guess what the CPU is going to want fetched next on the basis of what the last few fetches were. Many systems (car suspensions for example on expensive cars) have ways to look ahead and prepare for future demands. This is a common method of increasing efficiency. Why would our memories not have an automatic ‘lookahead’? Clues that we encounter should give us access to past experiences that may be helpful in the near future, and should do it immediately and without us realizing we needed that help. Those that are exceptional memories for one reason or another would become prominent in the stream of consciousness and if it is not obvious that the memory was prompted by this or that item in consciousness then it would appear to ‘pop’ in.