Response Latency

An important issue for the police and courts is the extent to which an eyewitness’s decision about a lineup can be trusted as accurate. Consequently, psychologists have searched for variables associated with the witness’s decision that help distinguish correct from incorrect decisions. One such variable is response latency (or response speed). Response latency is measured as the time elapsed from the witness’s first view of a lineup or photo array to their indication of a decision. A consistent relationship has been identified between the response latency and accuracy of positive identifications, but not of lineup rejections. Thus, fast identifications are more likely than slow identifications to be correct, while rapid and ponderous lineup rejections are equally likely to be accurate.

The rationale behind the investigation of response latency as a marker of accuracy is that witnesses who have a good memory of the offender should be able to determine whether any of the lineup members match their memory more rapidly than witnesses with a poor memory. Furthermore, response latency is compelling as a potential marker of accuracy for two reasons. First, unlike other potential markers of identification accuracy (e.g., confidence or self-reported decision strategy), response latency is a direct product of the identification task. Consequently, it is objectively measurable and not subject to the same influences as self-report measures. Second, response latency is correlated with other markers of accuracy (e.g., faster responses tend to be made with more confidence) without being identical to them. Thus, the combination of response latency and confidence may discriminate correct from incorrect decisions more effectively than either marker alone.

Although it has not been the focus of an overwhelming amount of research attention, investigations of response latency in eyewitness identification and face recognition have produced very consistent results. Specifically, a relationship is consistently observed between the response latency of positive identifications and the accuracy of those identifications, with the likely accuracy of an identification declining as the response latency increases. In contrast, studies equally consistently find no evidence for a relationship between the response latency of lineup rejections (i.e., responses that the offender is not present in the lineup) and the accuracy of those rejections. Interestingly, this pattern of a significant relationship with accuracy for choosers (i.e., positive identifications), but not nonchoosers (i.e., lineup rejections), parallels the findings regarding the confidence-accuracy relationship in face recognition and eyewitness identification.

Despite the consistency of the relationship between the speed and accuracy of positive identifications, this knowledge does not necessarily translate into a practically useful discrimination tool. For example, is a witness who takes 30 seconds to identify the suspect from a six-person photo array fast, and therefore likely to be correct, or slow, and likely to be incorrect? Researchers have attempted to address this challenge in two major ways. One involved the direct manipulation of response latency. However, attempts to produce high accuracy rates by forcing participants to make a fast identification were unsuccessful. Thus, it appears that the relatively short latency of accurate witnesses is the result, not the cause, of the decisions processes that produce accurate decisions. The other involved the suggested use of a specific time (i.e., 10-12 seconds) as the cutoff for distinguishing fast (i.e., reported in less than 10-12 seconds), and consequently accurate identifications, from slow (i.e., reported after more than 10-12 seconds) identifications, which were less likely to be correct. Despite the apparent early success of this rigid rule, subsequent studies demonstrated that the boundary between fast and slow decisions is not constant but varies from situation to situation as a result of changes in variables such as the target and lineup, the nominal size of (i.e., the number of members in) the photo array, and the retention interval between viewing the offender and attempting to make an identification from the lineup. The demonstrated instability of the border that separates fast from other identifications rules out the practical use of a universal response latency boundary to discriminate identifications with a high probability of being correct. However, subsequent analyses using this type of static response latency boundary (i.e., 10 seconds) in combination with a confidence criterion (e.g., identifications made with 90% or 100% confidence) have shown some promise. Although few decisions met both the response latency and confidence criteria, those decisions observed a very high accuracy rate across a number of stimuli and viewing conditions. Consequently, the most encouraging use for response latency appears to be in combination with other markers of identification accuracy—most notably confidence.

Response latency is often inappropriately referred to as decision latency (or decision speed). Although this may seem a pedantic, semantic distinction it underscores an important point about the measurement and use of response latency in the eyewitness identification domain. Specifically, an eyewitness, particularly a conscientious eyewitness, may not make a response immediately on arriving at a decision. For example, the attention of one witness with an excellent memory for the offender may be drawn to a specific lineup member as soon as he or she sets eyes on a photo array, and the witness could feel certain that the perpetrator has been found. However, to ensure that they have not made a mistake, these conscientious witnesses may continue to carefully examine each of the other lineup members before identifying the lineup member to whom their attention was initially drawn as the offender. In contrast, the attention of another witness with a relatively impoverished memory may not be drawn to any specific member of the lineup. Consequently, that witness may conduct a careful and deliberate examination of the lineup before making and indicating their identification decision. In other words, the observed response latency may be affected by factors other than the amount of time it took the witness to arrive at a decision (e.g., their conscientiousness or their confidence in their ability to make the correct decision).

At present, despite the consistent relationship between latency and identification accuracy, these findings do not lead to any practically useful methods for reliably discriminating correct from incorrect decisions, but the combined use of response latency with confidence judgments appears to be a potentially fruitful area of investigation.

References:

  1. Brewer, N., Caon, A., Todd, C., & Weber, N. (2006). Eyewitness identification accuracy and response latency. Law and Human Behavior, 30, 31-50.
  2. Dunning, D., & Perretta, S. (2002). Automaticity and eyewitness accuracy: A 10- to 12-s rule for distinguishing accurate from inaccurate positive identifications. Journal of Applied Psychology, 87, 951-962.
  3. Sporer, S. L. (1993). Eyewitness identification accuracy, confidence, and decision times in simultaneous and sequential lineups. Journal of Applied Psychology, 78, 22-33.
  4. Weber, N., Brewer, N., Wells, G. L., Semmler, C., & Keast, A. (2004). Eyewitness identification and response latency: The unruly 10-12 s rule. Journal of Experimental Psychology: Applied, 10, 139-147.

Return to the overview of Eyewitness Memory in Forensic Psychology.