Expert witnesses are widely used in criminal trials to add scientific confidence to proof. However, research by Loftus et al we know that eye witness testimony is extremely unreliable!
Psychologists such as Loftus are often called as expert witnesses for the defence to warn jurors of the possible problems with eye witness testimony. However, research has shown that jurors tend to disregard these warning and still believe eye witness accounts.
Cutler et al 1989 carried out a lab experiment to find out the effcet of using expert witnesses on jury perception of eyewitness testimony.
It was a videotaped mock trial in which 538 psychology students took part in.Ppts were shown a videotaped mock trial of a robbery. Afterwards they individually completed a questionnaire containing the dependent measures which were verdict, a memory test and rating scales of how confident they were in their verdict.
Cutler used a large sample size of 538 psychology students. This is good because a large sample size means a lot of data can be obtained, and generalised to a wider population. They also completed a questionnaire which means that both qualitave and quantitative data would be collected, therefore results can be analysed. However, they were all psychologist students, from chicago and northwestern ( not target population of amercica > Ethnocentric) who recieved credits for their course if they chose to take part, therefore they volunteered to be ppts. This is major problem as they could put on social desirablity and may attempt to figure out the aim of the study and give answers/act in a way as they think they think Cutler would be expecting. therfore this lowers the validity of the results.
The method used was a laboratory experiment. This is good as lab experiments allow cause and effects ( as you can see in the cutler study that when WICwas good, more guilty verdicts were given and this effect increased if the expert witness gave a descriptive testimony. Also i allows extraneous variables to be controlled. However, ecological validity of the experiment is low, as a videotaped mock trial was used. Therefore results found would be hard to generalise to the target population as it was not a real jury. However in real life jurors are sworn to secrecy, therefore no information about a case is spoken off. This makes
This study provides a cognitive explanation of how eye witness testimony can affect the jury's percpection. This is good because it helps us understand how our mental processes as human beings contribute to the information we recieve into our brains, and how it affects the way we think and percieve things. However it is reductionist, as it provides a simplistic explanation and ignores the issue that the mind may not be logical. people may think the way they do because of biological or social causal factors.