Fall 2009
Volume 3, Issue 1
Eye on the Future Research Focus
Research on Eyewitness Testimony
By Joe Vitriol and Jason Mandelbaum

Eyewitness testimony can be compelling evidence of a defendants guilt. Yet witness memory is not perfect and can be undermined by elements of viewing conditions and lineup procedures. Unfortunately, jurors are generally insensitive to these potential sources of error (Cutler, Penrod, & Dexter, 1990). Therefore, it is no surprise that inaccurate eyewitness testimony is a leading cause of wrongful convictions. The Innocence Project reports that eyewitnesses testified in 75% of cases in which the defendant has been exonerated by DNA evidence. How is it possible that a well-intentioned witness can unknowingly contribute to the conviction of an innocent person?

Social science researchers have distinguished two general categories of factors that can influence the accuracy of eyewitness evidence: estimator and system variables (Wells, 1978). Estimator variables are factors that are not under the control of the criminal justice system and usually occur at the crime scene. For example, research demonstrates that the longer a witness views a criminal, the more accurate their identification of a perpetrator in a lineup (Dysart & Lindsay, 2007). However, the relationship between exposure time and memory accuracy depends, in part, on the quality of exposure. Lighting, distance from the target and the perpetrators disguise are some factors that can affect the accuracy of the memory encoded.

Eyewitness memory can also be impacted by the stress induced by a criminal event, which can negatively effect the encoding of relevant stimuli by elevating psychophysiological responses (Deffenbacher, Bornstein, Penrod, & McGorty, 2004). Environmental factors at a crime scene can also influence a witness visual attention allocation to affect exposure time and quality. Consider, for example, the effect that the sudden, unexpected presentation of an attention-grabbing weapon (e.g., gun) may have on memory encoding. The presence of a weapon not only induces stress, but can also become the focus of a witness attention, reducing their ability to encode relevant information, including the perpetrators face (Steblay, 1997).

The aforementioned estimator variables demonstrate how specific features of a criminal event can influence the encoding of an eyewitness memory. Theoretically, if a witness has a strong memory for the perpetrator, s/he is more likely to make an accurate identification in a police lineup. However, the quality of an encoded memory is not the only factor influencing the accuracy of eyewitness evidence. In order for that information to be useful to criminal investigations, the memory must also be recalled accurately.

Factors that impact eyewitness recall and are controlled by the criminal justice system are known as system variables. Accordingly, much eyewitness research has investigated factors related to the construction and administration of lineups in an attempt to minimize the risk of recall error. For example, when viewing a lineup, witnesses may compare each lineup member and choose the one that best matches their memory for the perpetrator. However, the perpetrator is not necessarily contained in the lineup. By presenting lineup photos sequentially (one at a time), instead of simultaneously (all at once), eyewitnesses are forced to compare each photo directly to their own memory, not other lineup members (Lindsay & Wells, 1985). The sequential presentation of lineup photos improves the diagnosticity of police lineups by reducing the identification of innocent suspects who may resemble the perpetrator (Steblay, Dysart, Fulero, & Lindsay, 2001).

Eyewitness identifications can also be influenced by how the lineup is administered. For example, witnesses often believe that the police have arrested the guilty suspect, and may feel compelled to select the lineup member who most closely resembles the perpetrator. Research indicates that by instructing witnesses that the perpetrator may or may not be included in the lineup, error due to guessing can be reduced (Malpass & Devine, 1981). Furthermore, if the lineup administrator knows the suspects location in the lineup, s/he may inadvertently influence an eyewitness selection. Like any psychology experiment, double-blind administration of lineups can minimize the influence of administrator bias (Kovera & Greathouse, 2008).

Eyewitness research, on both system and estimator variables, has made enormous progress in recent decades. Still, in any given real-world case, researchers can only estimate the effect of these situational and procedural variables on the quality of an eyewitness memory and the accuracy of their lineup identification. Future research must continue to improve our understanding of the nature of eyewitness evidence, for the risk of wrongful conviction and the concomitant failure to apprehend guilty perpetrators remains an unacceptable consequence of witness error.

References:

Cutler, B.L., Penrod, S.D. , & Dexter, H.R. (1990). Juror sensitivity to eyewitness identification evidence. Law and Human Behavior, 14, 185-191.

Deffenbacher, K. A., Bornstein, B. H., Penrod, S. D., & McGorty, K. (2004). A meta-analytic review of the effects of high stress on eyewitness memory. Law and Human Behavior, 28, 687-706.

Dysart, J. E. & Lindsay, R. C. L. (2007). Delay between crimes and identification attempts: Too much speculation, too little data. In R. C. L. Lindsay, D. F. Ross, J. D. Read, & M. Toglia, (Eds) Handbook of Eyewitness Psychology: Memory for People, 361-375.

Greathouse, S. M., & Kovera, M. B. (2008). Instruction bias and lineup presentation moderate the effects of administrator knowledge on eyewitness identification. Law and Human Behavior, 33, 247-257.

Lindsay & Wells (1985). Improving eyewitness identifications from lineups: Simultaneous versus sequential lineup presentation. Journal of Applied Psychology, 70, 556-564.

Malpass, R. S., & Devine, P. G. (1981). Eyewitness identification: Lineup instructions and the absence of the offender. Journal of Applied Psychology, 66, 482-489.

Steblay, N.M. (1997). Social influence in eyewitness recall: A meta-analytic review of lineup instruction effects. Law and Human Behavior, 21, 283-298.

Steblay, N.M., Dysart, J., Fulero, S., & Lindsay, R.C. (2001). Eyewitness accuracy rates in sequential and simultaneous lineup presentations: A meta-analytic comparison. Law and Human Behavior, 25, 459-474.

Wells (1978). Applied eyewitness testimony research: System variables and estimator variables. Journal of Personality and Social Psychology, 36, 15461557.
Editor: Molly Petersen - Associate Editor: Peter M. Vernig