Exposure Time and Eyewitness Memory

When assessing the potential of an eyewitness, among the first things an investigator has to decide is whether or not the witness had an opportunity to observe what took place for a sufficient time. The decision is likely to be influenced by a witness's assessment of the length and quality of exposure to a perpetrator's face. A longer exposure can increase the ease with which details come to mind at the time of remembering and increase the likelihood that witnesses will correctly recognize a face from an identification lineup and provide a more detailed description. However, an extended exposure could make the witness more confident in their identification ability even when they are wrong. It has been recommended that investigators should not rely too heavily on witness confidence as an indicator of accuracy.

There are two points to bear in mind when examining the relationship between eyewitness memory and exposure duration. First, eyewitnesses are not very good at making estimates of the duration of a given event, and witnesses may overestimate the length of exposure to a face. Second, a longer exposure to a face can make a witness more confident in their ability to make an identification, although there are numerous other factors that could inflate (or deflate) a witness's confidence.

When witnesses are asked whether or not they could identify someone seen earlier, they will rely on various sources of information when making a judgment about the strength of their memory. One source of information that could influence their decision is “availability” or the ease with which information can be brought to mind. A longer exposure is associated with an increase in availability, and this can have interesting consequences for the accuracy of an eyewitness's identification.

Don Read was the first to examine the use of the availability heuristic in an eyewitness identification setting. He found that participants who interacted with store clerks for a longer duration (4–15 minutes as compared with 30–60 seconds) made a higher number of correct choices from lineups in which the culprit was present. However, it was found that the false identification rate in the target-absent lineups were inflated if the store clerks received additional information (cues) about the target. The latter finding fits with the hypothesis that availability of additional cues can sometimes lead a witness to believe that they have a stronger memory for the target, and in a target-absent lineup this can have potentially serious consequences.

The question of why an increase in exposure would lead witnesses to overestimate their ability to make an accurate identification from a lineup was explored by researchers at Aberdeen University using “mock” [Page 283]eyewitnesses (aged 17 to 81 years). The witnesses individually viewed a video reconstruction of a robbery at a savings bank. No weapons were seen in the video, although the culprit indicated to the clerk that he had a gun. The critical aspect of this video for the purposes of the study was the length of exposure to the culprit's face in the video. Two versions of the video were created. In one version, the culprit's face (full-frontal and profile view) was visible for 45 seconds, and in another version, the culprit's face (full-frontal and profile view) was visible for 12 seconds. No other details differed, and the videos were of the same duration (1 minute 40 seconds). About 35 to 40 minutes after witnessing the robbery, witnesses in the long-exposure group made more correct identifications of the robber when he was present in the lineup. They also provided more correct descriptions of the robber under the long-exposure condition. A longer exposure did not appear to inflate false identifications when the culprit was absent from the lineup in the Aberdeen study.

...