Someyearsago,aMiamiwomanwalkin-优题课

Some years ago, a Miami woman walking through an office building noticed two men standing together．Several minutes after her leaving, the men murdered a person working in the building．The police determined that the woman was the only witness and could possibly describe them．However, her memory of the men proved disappointingly unclear．Several days later, psychologist Ronald Fisher was brought in to obtain a more complete account from the woman．His interview produced a breakthrough—the woman reported a clear picture of one of the suspects．The important information enabled the police to arrest the suspect and close the case．
The police asked Fisher for help because of his rich knowledge in cognitive (认知) interview, a kind of memory-rebuilding process．Memory researchers have found that people trying to remember a past event often only recall part of the relevant information．Human memory is selective and it is often distorted by stress．But a person's accurate recall of an event or understanding of a question can be improved using specific interviewing techniques．The "cognitive interview" was developed in the late 1990s．It encourages the witness to take an active role in recalling information rather than giving answers only to someone else's questions．The witness first describes what happened in his or her own words, with no interviewer interruptions．The interviewer then goes further with specific techniques, such as having the witness tell the details of what happened from different perspectives（角度）.
The cognitive interview focuses on guiding witnesses through four general recalling techniques: thinking about physical surroundings and personal feelings that existed at the time of past events; reporting everything that comes to mind about those events, no matter how broken it is retelling events in a variety of time orders, such as from beginning to end, end to beginning, forward or backward; and adopting different perspectives while recalling events．
Experiments with police detectives trained in this demanding interview method find that they obtain nearly 50% more information from witnesses than before training, while error rates remain about the same．It is proved that cognitive interviews are quite important tools in improving the accuracy and completeness of witness testimony （证词）．

The purpose of the passage is to _____．