...To tell the truth and nothing but the truth

We frequently see in courtroom movie scenes when a witness goes to the platform, stands up and takes an oath “to tell the truth and nothing but the truth” --with the right hand raised up and the left hand on top the Bible. In reality, however, crime witnesses do not accomplish “to tell the truth and nothing but the truth” for they do not achieve full accuracy in their statements – whether consciously or unconsciously. 

When crime witnesses unconsciously display errors in their statements of the crime scene, they might have experienced a psychological term called change blindness. In visual perception, change blindness is a phenomenon that occurs when a person viewing a visual scene apparently fails to detect changes in the scene. Davies & Hine (2007) conducted an experiment with the intention to show the relationship between the eyewitness testimony and change blindness. In the experiment, a two-minute video clip depicted an opportunity theft from a student house. Halfway through the film, the actor playing the burglar changed identity.  A community sample of 80 people (40 men and 40 women) aged 15-65 years volunteered to participate in the study. The sample was randomly subdivided into two conditions – the intentional and incidental condition. Prior to the presentation of the video footage, the intentional condition participants were instructed to watch the film carefully because they would later be asked questions about it, whereas the incidental condition participants were told to watch a film about the dangers of unsecured property. Results have shown that only 31 of the 80 participants reported change (39%). In addition, 65% of the participants in the intentional condition noticed the change, compared with 12.5% of participants in the incidental condition. This explains that greater attention associated with a deliberate memory task would lead to a higher rate of change detection than the participants who were not primed to observe carefully.  In the change blindness scenario, variables such as familiarity of the target person, exposure time, and race demonstrably influence eyewitness identification. This shows that eyewitnesses achieve relatively poor accuracy when it involves unfamiliar people seen in brief encounters. So when eyewitnesses swore they told “tell the truth and nothing but the truth,” you might want to think about that one over again.

Graham Davies, & Sarah Hine. (2007). Change Blindness and Eyewitness Testimony. The Journal of Psychology, 141(4), 423-34.  Retrieved January 17, 2011, from ABI/INFORM Global. (Document ID: 1314578911).