In cases where a criminal’s identity is unknown to an eyewitness and investigators have not yet pinpointed a suspect, witnesses may be asked to search through a large number of photographs for a picture of the criminal. This process is known as a mug shot search because the photographs typically come from a database of photographs of arrested people (either computerized or from a file drawer system). Researchers have examined whether viewing hundreds of photographs in search for a criminal may have detrimental effects on a witness’s memory of the criminal or later identification accuracy. Specifically, researchers have focused on three potential effects: interference, unconscious transference, and commitment. Regardless of the effect, one caveat with this body of research to date is that it has not yet been tested with real-world witnesses in real criminal cases.
Interference, in mug shot research, is when postcrime information, in the form of viewing many new faces, weakens or interferes with the witness’s memory of the actual criminal. Interference is most commonly tested in research laboratories by exposing two groups of participants to a mock crime, asking one group to look through mug shot photographs and then asking both groups of witnesses to make an identification of the criminal from a six-person lineup. Researchers also manipulate whether or not the mock criminal’s photograph is present in the lineup to test whether or not witnesses who viewed the mug shots are more likely to choose an innocent person when the actual target is not present. Although it is reasonable to assume that the process of viewing hundreds of faces in search for a criminal may influence a witness’s ability to later make a correct identification of the criminal, research results to do not support this assumption. Research has shown that viewing mug shots has virtually no effect on later identification accuracy from lineups.
Unconscious transference from viewing mug shots refers to the event in which an innocent lineup member, who is also the only lineup member previously viewed by the witness in a prior mug shot task, seems more familiar than do the other lineup members because he was viewed in the mug shots. The concern is that this sense of familiarity on the part of the witness may lead to an increased rate of selection of the (only) lineup member who was seen previously in a mug shot task. The phenomenon of unconscious transference has likely plagued most adults at one time or another as evidenced in the common question, “Where do I know that face?” For witnesses who view mug shots, followed by a lineup that contains one person seen in those mug shots and five photographs never seen before, they are faced with a similar question. The correct answer is for witnesses to say, “I saw that face in the mug shot task,” and the erroneous conclusion is that the face is familiar because it is the face of the criminal.
Support for unconscious transference from mug shots is mixed, with only a few published studies finding support for the effect. Researchers have manipulated variables such as the number of mug shots viewed (from 10 to more than 600) and the delay from viewing the mug shots to the lineup task (immediately to several weeks later) but have been unable to find a consistent predictor of the unconscious transference effect.
Commitment refers to the event when a witness selects a (innocent) person from a mug shot task and then selects the same (incorrect) person from a later lineup procedure. Research on the commitment effect is consistent in that it is relatively easy to produce and that it has the largest negative impact on lineup identification accuracy when considered with the other two effects described above. In one research example, almost two-thirds of witnesses who selected an innocent person from a mug shot task went on to later identify that same innocent person from a lineup. A comparison group of participants who did not see mug shots picked the innocent person at a rate of only 20%.
As with any identification procedure, there are numerous ways that investigators could conduct the mug shot task that may have differential effects on the outcome. Some procedural variations that have been examined include whether the photographs are sorted by gender, age, race, and type of crime before viewing; the ideal number of mug shots to view; and whether a computerized sorting system yields more accurate identification results than do standard mug shot methods.
In sum, mug shot research has not supported the intuitive concerns that interference and unconscious transference effects generate. Commitment to a photograph, however, does seem to be a strong predictor of identification errors from mug shot searching. Regardless of the area of research described above, an increase in real-world data obtained from field studies will be highly beneficial and informative for future mug shot research.
- Deffenbacher, K. A., Bornstein, B. H., & Penrod, S. D. (2006). Mug shot exposure effects: Retroactive interference, mug shot commitment, source confusion, and unconscious transference. Law and Human Behavior, 30, 287-307.
- Dysart, J. E., Lindsay, R. C. L., Hammond, R., & Dupuis, R. (2001). Mug shot exposure prior to lineup identification: Interference, transference, and commitment effects. Journal of Applied Psychology, 86, 1280-1284.
- Gorenstein, G. W., & Ellsworth, C. (1980). Effect of choosing an incorrect photograph on a later identification by an eyewitness. Journal of Applied Psychology, 65, 616-622.
- McAllister, H. A., Stewart, H. A., & Loveland, J. (2003). Effects of mug book size and computerized pruning on the usefulness of dynamic mug book procedures. Psychology, Crime & Law, 9, 265-277.