"Many experts are challenging the view that eyewitnesses recounting what they saw is the best way of tapping their memory. Some think brain scans could be the way forward." [Memory Mixup, BBC News Magazine, 17 June 2008]
We already have technology that is supposed to detect discrepancies between what the witness remembers and what the witness says - it's called a polygraph or lie detector. Now we apparently need another technology that detects discrepancies between what the witness consciously remembers and what is buried in the witness's unconscious.
The lie detector has been controversial ever since its invention, and features in a Chesterton story called "The Mistake of the Machine". (Of course it is not the machine that makes the mistake, as Chesterton's hero Father Brown points out, but the people using the machine who misinterpret its output.)
- Chesterton and Friends: Lie Detectors
- David Wallace-Wells: The Big Lie (Washington Monthly, April 2007), via AntiPolygraph.org
Of course humans sometimes lie, and sometimes this can be detected by the polygraph, but that doesn't make the polygraph an instrument of truth. (For that matter, people sometimes blurt out secrets under the influence of alcohol or torture, or get artistic inspiration under the influence of mind-bending drugs, but none of these are reliable instruments of truth either.)
And human memory is sometimes unreliable, but that doesn't make the brain scan an instrument of truth either. Constructing evidence from the unconscious contents of a brain is no more reliable than constructing history from an archaeological sift through a mediaeval rubbish tip. It may be possible, and may yield some intriguing results, but the results are always speculative and uncertain.
Meanwhile, our "common sense" understanding of the brain and its contents is probably less accurate and less coherent than our understanding of mediaeval waste disposal. That's why psychoanalysts make more money than archaeologists. They do, don't they?
"India has become the first country to convict someone of a crime relying on evidence from this controversial machine." [Source: New York Times, via Bruce Schneier]