Deffenbacher, Bornstein, Penrod, and McGorty (2004) conducted a meta-analytic review intending to determine the effects of high levels of stress on memory of eyewitnesses. It was argued that much of the confusion in determining the effect of stress on memory was because many studies do not actually push participants to a high enough stress level. This review excluded any studies that did not elevate participant's stress level to elicit a defensive response or activation mode of attention control. This defensive response as defined by Deffenbacher et al is characterized by a pronounced change in physiological measures of stress. These measures include increased heart rate, blood pressure and muscle tone (2004). Two meta-analysis were conducted in this review. One attempted to determine whether stress impacted the ability of an individual’s facial recognition. Moderator variables were also examined that might impact the results of these studies. The second analysis examined the accuracy of eyewitness recall of details and the impact of stress. Additionally, the effect of other variables which may have influenced detail recall were also examined.
The conclusion of the first analysis was that stress did in fact have a negative effect on eyewitness identification accuracy (Deffenbacher et al., 2004). This is the outcome that was expected, however numerous other variables were discovered to have an impact on whether eyewitness memory was found to be impacted by stress. These variables were; lineup type, research paradigm, presence or absences of a staged crime, and witness age.
Lineup type, meaning either a target present (TP) or target absent (TA) was found to moderate the effect of stress on memory. Target present lineups had a moderate effect size on accuracy of face identification. Individual's who were in a low stress group had better facial identification than those in the high stress group in terms of correct hit rate (0.59 verses 0.39). However for the target absent lineup group there was no difference between the high and low stress participants in their ability to correctly reject the line up. It was hypothesized by Deffenbacher et al. that stress did not degrade the visual representations in memory enough to affect an individuals ability to decide that a face was not in the lineup. Additionally, high stress elevated false alarm rates in TP lineups. This supports the hypothesis that stress degrades memory and reduces a witness reliability when exposed to stress during the witnessing of an event.
The method in which the research was collected also has an impact on the ability to correctly identify a face. The two methods examined were the “standard face recognition task” and “eyewitness identification paradigm” (Deffenbacher et al., 2004). The eyewitness identification paradigm It was found that the former was impacted by high and low stress conditions. Stress did not have a statistically significant impact on the standard face...