1.3 Verbal overshadowing
It is possible that asking the witness to provide a verbal description of the culprit may make it harder for them to subsequently identify the culprit in an identification parade. This means the amount and type of evidence obtained from a witness is another factor that can affect the accuracy of eyewitness identification.
If you need to remember an address or phone number and cannot write it down, repeating it over and over can help commit it to memory. Psychologists refer to this as ‘rehearsal’ and rehearsing information is generally seen as very beneficial to memory – it is essentially the basis of exam revision for example. However, while rehearsal can help with our memory for ‘facts’, there is some evidence that it can harm our memory for more complex and subjective experiences such as witnessing a crime.
In Week 5 we explored how difficult it can be to describe a face, and that verbal descriptions of faces tend to be inaccurate. Describing the face of a perpetrator involves rehearsing the information about their appearance – but does rehearsing incomplete or inaccurate information aid or harm memory?
To answer this question, Schooler and Engstler-Schooler (1990) showed participants a video of a crime scenario and then asked one group to provide a verbal description of the face of the perpetrator, a second group to form a visual image of the target’s face and a third group to do nothing. All three groups were then asked to identify the target from a line-up.
Those who were asked to produce a verbal description were significantly less accurate in choosing the target than the other two groups, whose results were similar. In other words, not only did rehearsing the information about the face of the target not aid memory, it actually seemed to make it worse.
The researchers suggested that the group asked to verbally describe the face may then have used this verbal memory of the face when they were asked to identify it – rather than the visual memory that would have been more accurate and that was used by the other two groups. Another way to see this is that by describing the face, a verbal memory was formed that somehow overwrote or ‘overshadowed’ the original visual memory.
This effect has become known as ‘verbal overshadowing’ and has been replicated in subsequent research. It is thought to resemble the effect of post-event information, in that the witness’s memory of the original crime is ‘overwritten’ or altered by information encountered afterwards.