Eyewitness Identification

  1. Human memory does not operate as if it were a videotape camera. We do not simply record some event in our memory and then later retreive an unblemished recollection of what happened.

  2. Human memory is much more fragile, suggestible, and prone to distortion and decay than we typically realize. As a result, mistaken eyewitness testimony rarely involves outright lies; instead, it usually corresponds to commonly occurring distortions in memory functioning.

  3. Memory consists of three stages: (1) storage, (2) retention, and (3) recall. Storage factors can impede memory accuracy when we find ourselves unable to recall information from our memory because it was never stored there. For instance, can you recall which way Lincoln faces on a penny, and where the letter identifying the mint of the penny is located?

  4. The penny example demonstrates that when we experience some event, our brain makes an instaneous decision whether to store information related to that event - or simply disregard it. The decision to store or disregard corresponds to how we evaluate the event - something worth remembering or merely a trivial circumstance?

  5. The influences of the retention stage can corrode memory via three factors: (1) passage of time, (2) frequency and length of exposure, and (3) new information. Surprisingly enough, memory not only fades away with the passage of time - it also grows and expands.

  6. What fades from memory over time is the actual experience of an event. Consequently, each time we recall some event we must reconstruct it - asking ourselves what happened and how it transpired - and with each reconstruction our memory can change. Therefore memory recall, or the reconstruction of some event, responds primarily to our sense of what is plausible. We actually recall bits and pieces of information and fill in the gaps with inferences or "educated guesses."

  7. Our memory for faces can persist for years. For example, we might return to our high school reunion and recognize numerous faces and remember many names. Nevertheless, we must consider how we were repeatedly exposed to those faces for as long as four years. Under conditions of brief, one-time exposure, our memory for faces rapidly declines. The question of how accurately we can remember a face ultimately involves how many associative links exist with that face? Very few links exist after a brief, one-time exposure; but many links develop over a period of four years. When exposed only briefly to some event an accurate recall of that event after three to four weeks is unlikely.

  8. After witnessing an event, we are sometimes exposed to new information that can actually change our memory. What is known as the "post-event information effect" often transpires as a result of our dialogues with other people. For example, an eye-witness to some event frequently discusses with others what they saw. In the aftermath of some event, the eyewitness and others may speculate as to exactly what happened, the sequence in which it occured, and the degree to which various participants were involved. Rather than facilitate reproductive memory - the accurate reproduction of some past event, an eyewitness' dialogues with other people create reconstructive memory - a reconstruction of the past which may be quite inaccurate because it responds more to considerations of plausibility than fact. Therefore, people can reconstruct inaccurate memories after witnessing some event as a result of discussing that event with other people.

  9. Because of how fragile and suggestible memory is, line-up procedures can result in tragic errors. In particular, simultaneous line-ups - a witness views the suspect along 3-5 other individuals at the same time - are inappropriate. Simultaneous line-ups lead witnesses into making relative identifications - relative to each other, which of these individuals most looks like the suspect?

  10. Sequential line-ups - the witness views each person in the line-up one individual at a time - are the appropriate procedure. Sequential line-ups lead witnesses into making more absolute identifications - does this person look like the suspect? As a result, sequential line-ups significantly reduce the number of false positive identifications compared to simultaneous line-ups.

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© 2011 Dr. Terence W. Campbell, Ph.D., ABPP