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The suggestibility effect

15 October 2007

Alexandra Bright-Paul and Christopher Jarrold from the Department of Experimental Psychology set out to investigate why memory confusions occur frequently in children.

Participants in studies of this nature are generally asked to witness an ‘event’, such as watching a film. They are later subjected to information that contradicts key elements of that event. Later still, they are tested for their memory of the original event.

A common finding is that individuals, and in particular young children, incorporate the misleading information into their reports of the original event.

One set of explanations proposes that suggestibility results from individuals misremembering the ‘source’ of experiences. Even when details of events are remembered accurately, individuals may nevertheless have difficulty remembering when or where they had occurred. However, what is less clear is why memory for source is poor. Two accounts offer alternative possibilities. Fuzzy-Trace Theory suggests that the origins of experiences are remembered as a separate aspect to the experience itself. With the passage of time, the memory of the source ‘fades’ and as a result its link with the memory of the experience becomes progressively weaker. This theory predicts that individuals will make more errors in remembering the origins of their experiences if more time has elapsed since the time of remembering it. In contrast, the Source-Monitoring Framework suggests that we make inferences about where and when we experienced memories, by evaluating them at the time of remembering. This account suggests that source errors are more likely when the sources themselves are less ‘distinctive’.

Memories for events do not simply fade away over time

We explored ‘fading’ and ‘distinctiveness’ explanations in one large study by examining how the time-delays between event, misinformation and test phases of the procedure affect suggestibility. We examined ‘fading’ by simply examining whether memory confusions were more likely when the gap between the event and being tested was lengthened. For example, this theory would expect that memory would be poorer 24 days rather then 12 days after an event. However, testing the ‘distinctiveness’ explanation was more complex so we adapted an established theory of ‘temporal distinctiveness’ typically applied to short-term memory. For this we calculated a ‘distinctiveness ratio’, which was the size of the time gap between the event and the misinformation, relative to the size of the time gap between misinformation and recall. For example, if two events are separated by three days and then recalled nine days later, memory confusions will be similar to those from two events separated by six days and recalled 18 days later (the ratio is 1:3 in both cases). This theory suggests that the time between the event and recall is irrelevant, and that only the apparent spacing between events influences memory errors.

In our study 150 five-year-olds watched a film (the ‘event’). At a specified later date they listened to a story that was a misleading version of the event (the ‘misinformation’). Finally, we tested their memory by giving them pictures that showed items that had appeared in either the event only, the misinformation only, both the event and the misinformation, or new items they had never seen before. They were asked to post each picture into one of four boxes that corresponded to the four options: seen in the film, heard in the story, seen in the film and heard in the story; and completely new. For half of the children the time interval between the event and the test was 12 days, and for the remaining participants it was 24 days. Within each group there were five different distinctiveness ratios of event-misinformation/misinformation-test delay (11:1, 3:1, 1:1, 1:3, 1:11). In other words, taking the first ratio (11:1) as an example, for the first group there were 11 days between watching the film and being told the misinformation story and one day between the story and being tested, and for the second group there was 22 days between watching the film and being told misinformation story and two days between the story and being tested.

These findings inform us about how child witnesses may confuse memories

One way in which we measured suggestibility was by looking at the number of items that had only been presented in the misinformation phase, but which the child said had occurred in the event. The results showed that the length of the delay between the event and the test did not significantly affect this type of memory confusion, implying that memory for context does not fade over time. Even when the time between the event and the test was lengthened from 12 to 24 days, the number of errors was similar if the ‘distinctiveness’ ratio remained the same, eg, three days/nine days or six days/18 days (1:3). However, the ‘ratio’ of the two intervals did significantly influence how well the children performed. When the distinctiveness ratio was large (ie, the event and misinformation were widely spaced apart) children were much less likely to confuse the misinformation for the event.

This research provides the first empirical demonstration that relative delays are more influential than absolute delays in determining the magnitude of suggestibility. This in turn suggests that memories for events do not simply fade away over time, however intuitive the idea of decaying memories may seem. Rather, we confuse the details of events that occurred in relative proximity. This is probably because memory traces interfere with one another, and the degree of interference will be largest when we think back to events that, relative to the point of recall, are closely bunched together in time.

In practical terms, these findings are informative about the ways in which child witnesses may confuse memories. On the positive side they imply that children will not necessarily forget events that occurred to them simply as a result of the passage of time. However, they also indicate that information about the context in which events occurred is subject to interference, and that young children will be particularly suggestible to misinformation when that occurs relatively close to the event and relatively far from the point of recall.

In a forensic context, in which children are serving as eyewitnesses in criminal proceedings, it is important to bear in mind that suggestibility is likely to be highest when there is a small gap between the event in question and any potentially misleading questions, coupled with a long gap between these questions and the child’s testimony itself.

Dr Alexandra Bright-Paul & Dr Christopher Jarrold / Department of Psychology

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