Intended and unintended effects of explicit warnings on eyewitness suggestibility: evidence from source identification tests.

Previous studies have shown that source identification (ID) tests reduce, and in some cases eliminate, eyewitness suggestibility errors. The present study showed that the suggestibility errors participants committed on a source ID test were further reduced when they were given the explicit postwarning that the experimenter was trying to trick them. These postwarnings reduced suggestibility to the same extent as prewarnings, and they did so for both once and repeatedly suggested items. In addition, the benefits of the pre- and postwarnings persisted when participants were retested 1 week later, but only if the suggestions had been repeated. For once-suggested items, the warning had the unintended effect of improving old/new recognition of the suggested information at retest, an effect that offset the improvements in source discrimination accuracy conferred by the warning. The advantages of using source ID tests for investigating group differences in eyewitness suggestibility are discussed.