How much detail can you reliably recall in your childhood memories? Actually very little, according to a new study with profound implications for our legal system.

Writing in the Quarterly Journal of Experimental Psychology, three UK-based psychologists asked 127 people to recall four of their earliest childhood memories about which they were absolutely certain. They were also asked questions about specific details.

When the results were analysed, the researchers found that participants were much more likely to remember some sorts of details than others. The 'what', 'where' and 'who' were commonly remembered. Other details - what the participants were thinking at the time, the weather and their age - were less likely to be recalled. The time of day the event took place or what they were wearing were even less likely to be recalled.

This matters because in many cases of alleged child abuse, memories, often "quite remarkably overly specific" memories, are "the only evidence". The authors of the study, Christine Wells, Catriona M. Morrison and Martin A. Conway, warn that: "Jurors and other triers of fact often respond positively to overly specific memory evidence [...] and in the UK at least, many convictions are made on the basis of this type of evidence. With sentences [for those found guilty] in years, sometimes a decade or more, the question of what adults can remember of childhood events that they claim to accurately recall is then critically important."

Prosecutors often use the fact that their adult clients can recall very specific details of childhood events as "powerful evidence" that certain incidents occurred. But as Wells and her colleagues state: "There is no simple relationship between accuracy [of memories] and the details, of any type, that can be recalled."

The authors conclude that "some confidence can be placed in the recall of the who, where, and what of a confidently remembered childhood event; other specific details are, however, less likely to be recalled." They suggest that what we might think of as detailed childhood memories are in fact our brains non-consciously 'filling in' "specific details that have not in fact been remembered".

Wells and her colleagues are clear about the implications of their work: "Courts and other settings where memory is the evidence need to be made aware of what is typically recallable, what is rare and unusual, and what seems unlikely ever to be recalled."

This new study gives those in the legal and caring professions a "normative profile" of adult accounts of childhood memories, to help them sort out childhood fact from adult fiction.