By Keir Liddle
The validity of eyewitness testimony is highly contentious but is also, conversely, one of the bedrocks of evidence in courtroom trials; no doubt due in some small part to the appeal of anecdotal evidence to simple little homo sapiens like ourselves. People have been convicted to lifetime imprisonment and the gallows on the basis of convincing eye witness statements. Yet there are many reasons to assume that eye witness testimony is often dubious and untrustworthy.
Social psychologists have found that while we may be careful and rigorous in our gathering of information about a product/service, say purchasing a new car and checking out reliability statistics for a thousand odd miles or models, one persons anecdotal evidence can override our carefully gathered information. Say we trawl through all the reliability statistics and discover the most reliable car then one person claims to know someone who owned the car the statistics says is most reliable and it always broke down. For some reason the argument presented by another person is more salient then the information or evidence we have already gathered and it will be unlikely that we will actually buy the reliable car based upon this.
In a courtroom setting this is worrying as it perhaps implies that we are less at the whim of the evidence but at the whim of charismatic, well spoken defence and prosecution lawyers. Who will use all sorts of rhetorical techniques to achieve their desired outcomes one of the more dramatic gambits being to deliberately transgress the etiquette and internal rules of the court: When they, possibly deliberately, say something that the judge is duty bound to strike from the record. This has been shown to be advantageous by research that shows information struck from the record salience is increased in the eyes of the jury. It’s a clever, if morally dubious, technique which makes the information they have imparted, with disregard for the courts procedures and rules, seem like a forbidden fruit to the jury and thus more important.
To get an idea of the attraction of forbidden knowledge try not to think of a white bear…
The above could be an argument for evidence to be submitted to the jury pre-recorded and edited after questioning by lawyers. Yet it is not just sneaky lawyer tricks we must be wary of in the courtroom. We have to beware of eye witness testimony as well – as research by eminent psychologist Elizabeth Lofthus, and many others, suggests that memory and eye-witness testimony is highly unreliable.
Lofthus and Palmer asked participants to estimate the speed of cars by asking different questions: “How fast were the cars going when they hit/smashed/etc?” unsurprisingly they found the words used to frame the question greatly effected the participants estimates. They concluded that evidence is easily distorted depending on the questioning technique used and that information acquired after the event can be incorporated into the memory of the event itself.
Experiments conducted by Barbara Tvernsky and Elizabeth Marsh further details another issue with eyewitness testimony the vulnerability of human memory to bias. In one group of studies participants were given the “roommate study” a description of incidents involving one of two fictitious roommates. Later participants were asked to recount these incidents in a neutral fashion and write a letter of recommendation for the roommate or to write a letter complaining about the roommate. They found that those who had written positive letters recalled the fictitious roommate incidents more favourably than those who had written negative ones.
This is perhaps related to Robert Cialdinis weapon of influence – commitment and consistency. It also perhaps has implications for trial justice, if you consider that in the experiment just writing a negative letter coloured the participants views of another person, in that perhaps just the effect of seeing the suspect in the dock or the act of giving evidence against them will influence past memories of event. Or more succinctly that seeing someone in a dock might prime a person to reassess their memories and report them with a negative slant – although it’s perhaps likely this will depend on whether the individual is a witness for the defence or the prosecution.
Eye witness testimony, is still considered highly reliable as a source of evidence yet much of the research in this area shows it to be highly unreliable.