Abstract
Eyewitnesses are an essential component of effective police investigations. The evidence that eyewitnesses provide can be fundamental to understanding a crime, and crucial to the successful apprehension and prosecution of offenders. Even multiple eyewitnesses viewing the same event and interviewed under the same conditions, however, can provide eyewitness accounts that differ substantially. Due to the persuasive nature of eyewitness evidence, inaccurate eyewitness reports have the potential to lead to wrongful convictions. It is therefore essential to understand the individual difference factors that might be involved in the provision of accurate and complete eyewitness reports. In this two-part thesis, I examine the relative contributions of individual differences in age and cognitive abilities that could relate to individual’s ability to provide two distinct forms of evidence: visual eyewitness evidence and verbal eyewitness evidence.
Part One
In Study One, I examine the relative contributions of age, executive function, and memory ability on eyewitnesses’ accuracy on photographic lineups. During the experiment, children (9-12 years old), adults (18-28 years old), and older adults (61-84 years old) viewed six brief film clips depicting a minor non-violent crime. After a brief delay, participants completed a six-person photographic lineup task. Over the course of the study, each participant saw three lineups that contained the perpetrator (target-present lineups) and three lineups that did not contain the perpetrator (target-absent lineups). To assess memory and executive functioning, participants were administered three subtests from the Delis-Kaplan Executive Function System and the four subtest memory screening measure from the Wide Range Assessment of Memory and Learning (WRAML-2).
The results showed that participants were relatively poor at the lineup tasks, generating an average accuracy rate of 45% on target-present lineups and 50% on target-absent lineups. Age group and measures of executive function were related to participants’ overall lineup accuracy (14.7% of variance explained) and target-present lineup accuracy (10.9% of variance explained). Executive function explained a small amount (3.9%) of the variance in target-absent lineup accuracy scores.
Part Two
In Study Two, I explored individuals’ verbal eyewitness testimony and examined the roles of age, intelligence, and memory ability on the quantity and quality of the information reported. A community-based sample of children (9-11 years old), adults (25-56 years old), and older adults (62-85 years old) were shown one of three brief film clips. After a 45-minute delay, participants were interviewed about the film clip using best-practice cognitive interviewing techniques. Participants were also administered the two subtest abbreviated intelligence measure from the Wechsler Abbreviated Scale of Intelligence and the four subtest memory screening measure from the WRAML-2.
Across the full memory interview, participants described an average of 96 unique details from the film clip, with an average accuracy rate of 77%. The individual difference measures of age, intelligence and visual memory explained 33.8% of the variance in the quantity of information reported, and age and visual memory ability explained 18.6% of the variance in the accuracy of this information.
Taken together, the data reported in this thesis demonstrate the fallibility of eyewitness evidence, and the roles that various factors inherent to the individual play in its provision. The measures included in this thesis, however, only explained a small amount of the variance in our eyewitness evidence measures, indicating that other factors are involved. To conclude this thesis, I describe some other factors that may contribute to eyewitness testimony and discuss the implications of this research.