I Tweeted him as to whether he really though there would be no situations in which eyewitness testimony would be sufficient for conviction. He did not respond to my Tweet. However, the following day, assuming he got several Tweets about this, wrote on Twitter:
Eye Witness Testimony: High evidence to the Courts. Warped evidence to the Psychologist. Low evidence to the Physicist.It was then that I recalled what I had learned in Psych101. And I went Google searching about the reasons psychologist find trouble with eyewitness testimony. I will synthesize some of that information I found and also break it down myself as to why it would be problematic to rely on eyewitness testimony alone in legal procedure or as evidence in the sciences.
The problem of eyewitness testimony really breaks down into three subsets of problem areas: a problem of perception, a problem of memory, and a problem of testimony. First, looking at perception. Please watch the following video. And please follow the instructions given.
Perhaps you have seen the video above before. Whatever the case, it and videos like it demonstrate that ordinary perception requires attention to details, sometimes astonishingly, big fat details. If a person is not careful, they will miss things that are right before the eyes. As hitherto mentioned Neil deGrasse Tyson one said, optical illusion books should be referred to as perceptual failure books since what is really happening is that your brain is failing to perceive properly what is right in front of your eyes.
The second problem with eyewitness testimony is the problem of memory. Remembering a fact or experience or situation is not like retrieving a file from a file cabinet. As much as it may seem at first glance that what we're doing when we remember is just revisiting the same memory, each time you remember something you are literally re-membering it: reconstructing it. And this interpretive and reconstructive process takes place just as soon as you receive information. Consider being in a public place and overhearing an argument. This argument will later be a make-or-break situation in a courtroom. But at the time you don't know that. You only hear keywords. It's not your conversation. You don't know the people who are having the argument. So ultimately you are filtering out a lot of what you hear and interpreting and reinterpreting the conversation, or failing to, as you hear more. Now, imagine later you are on the witness stand and asked to recall this argument. Imagine also that now you know some basic facts about the trial, the role this argument would play in the court, the value of your testimony now, etc. Even with the best intentions, you are not recalling a conversation you only gave half an ear to, which you have since had time to reinterpret it and perhaps magnify in importance. Don't you see how this could be a problem?
Finally let's consider the problem of testimony. Playing the telephone game where the story begins one way and being passed along inevitably leads to the filtering of certain information, as with the memory case mentioned earlier. The actual testimony, the actual way you phrase the events that happen, can easily be shaped by the person you are talking to. For example, if testifying about a car wreck the subtle use of a lawyer's substituting the verb 'crash' for 'hit' could make you think a car wreck occurred at a higher speed. For example, 'And when did you see the defendant crash cars with Mr. Smith?' This small locution creates a frame and makes the person testifying think and speak within that frame. There are other kinds of problems with actually relaying the information as well because sometimes one's verbal skills are not as good at conveying facts as one's head might be at remembering them. There could be, potentially a big gap, between what a person thinks and what a person says. Again, this is even if someone is well meaning.
Most of what I have said has focused on the use of eyewitness testimony in the courtroom. But it could be just as easily applied to eyewitness testimony for the sciences and could cover a whole range of things: supposed miracles that people have seen, which could just be simpler, as-yet-explained phenomena, or UFO sightings, which, um, ditto. So I think the problems with eyewitness testimony should make us all more modest in our claims and more vigilant about what we accept when people make a claim to something or when we ourselves have to make a claim in the role of giving eyewitness testimony.
And also we have to remember that ultimately problems of eyewitness testimony are problems of perception, memory, and testimony, all of which we commonly take to be sources of knowledge.