Alcohol Intoxication Impact on Eyewitness Memory

Alcohol consumption has a significant effect on eyewitness identification abilities, including the accuracy of perpetrator descriptions and identification accuracy in showups (an identification procedure where only one individual is shown to the witness) and lineups (an identification procedure where several individuals, usually six in the United States, are shown to the eyewitness). Understanding the effects of alcohol consumption on memory is critical for the police, investigators, prosecutors, defense counsel, judges, and jurors to be able to judge the veracity of statements and evidence that are put forward in cases where alcohol consumption was present.

The research to date that has examined the effects of moderate levels of alcohol intoxication on eyewitness memory and identification accuracy has found that intoxicated witnesses are less likely to be accurate in their descriptions of events and people but are just as likely as sober witnesses to make a correct identification decision. In addition, intoxicated witnesses may be more susceptible to suggestion and suggestive procedures than are sober witnesses. However, as research has suggested, this finding should not necessarily be taken to imply that intoxicated witnesses are always less reliable than their sober counterparts.

Ethyl alcohol, or ethanol, is a depressant that is produced by the fermentation of yeast, sugars, and starches and is most commonly found in beer, wine, and liquor. After it is ingested, alcohol is metabolized by enzymes in the liver. However, because the liver can only metabolize small amounts of alcohol at a time, the remaining alcohol is left to circulate through the body until it can be processed. Alcohol impairs judgment and coordination as well as attention level, and the more alcohol consumed, the greater the impairment. For example, in all states in the United States, the maximum level of blood-alcohol concentration (BAC) that is permitted to be under the “legal limit” for driving a motor vehicle is 0.08% (80 mg/dl). However, the effects of alcohol intoxication as described above are likely to be present at BACs much lower than is set by the legal limit.

Although scientists and researchers know that alcohol consumption causes reduced coordination and impaired judgment, the effects of alcohol intoxication on memory has received little attention from psychology and law researchers. One of the potential reasons for this is that previous research has focused on the effects of alcohol from a public safety perspective (i.e., setting legal limits for driving) and not from a victim or witness perspective. However, given that there are more than 450,000 violent crimes in bars and nightclubs every year in the United States (and therefore more than 450,000 victims/witnesses who are likely to have consumed at least some alcohol), research on this topic is extremely valuable. The general findings from the few research studies that have investigated the memory and identification abilities of intoxicated witnesses are described below after a brief review of alcohol decision-making theory and a description of the research methodologies that are used in this field of research.

Theoretical Review

Not long ago, researchers believed that alcohol acted as a general disinhibitor that resulted in risky decision making, best characterized by the phase “throwing caution to the wind.” However, the disinhibition hypothesis was unable to account for the finding that in some situations an intoxicated individual would become aggressive, whereas at other times the same individual would become depressed or happy. In an attempt to account for these disparate reactions to alcohol consumption, alcohol myopia theory was proffered. According to this theory, intoxicated persons, due to their limited cognitive capacity as a result of their alcohol consumption, are able to attend only to the most salient aspect in their environment. For example, a sober person is capable of having a conversation with another person while attending to other events in the surroundings, such as a new person entering the room. An intoxicated person having the same conversation, however, is much less likely to notice peripheral details in the environment. Similarly, intoxicated persons are more likely than sober persons to take into account only the immediate cues in their environment and to have a limited capacity to consider or bring to awareness other information, such as the consequences of their behavior.

Alcohol Research Methodologies

Although the research literature on this topic is limited, a discussion of the types of research methodologies that are most common when investigating the effects of alcohol on eyewitness memory is warranted. Two of the most common techniques are laboratory research and field studies.

Laboratory Research

Laboratory research on this topic involves (a) pre-screening participants for any factor that would make them ineligible for alcohol consumption research (e.g., underaged participant or pregnant female), (b) obtaining the consent to participate, and (c) administering alcohol. The amount of alcohol given is calculated on a participant-by-participant basis and takes into consideration the following factors: the desired BAC, the concentration of the alcohol being administered, and the participant’s sex and weight. The alcohol is generally administered over a period of 30 to 45 minutes, and after a short period of time (for adsorption), the stimulus (e.g., video clip of a taped mock crime or an interaction with a confederate) is then presented to the participant. Next, depending on the particular research question, the participants may be asked to complete the dependent measures while still intoxicated, or they may be asked to return for a follow-up session, where they will be sober when they complete the dependent measures. Regardless of the research question, for safety purposes, all participants in this type of research must be relatively sober before they are permitted to leave the research lab. To ensure that participants’ BAC is low enough for them to be excused (usually 0.03% or lower, as set by individual institutional review boards), a breathalyzer is used. It should be noted that although a blood-test analysis could also be conducted in lieu of a breathalyzer, this practice is not normally used by psychology and law researchers. Also, laboratory research is limited with regard to the amount of alcohol that can be safely administered to participants. Although there may be exceptions depending on the location (country) of data collection, the research question, and individual IRBs, generating BACs in the lab greater than 0.08% is rarely permitted.

Field Studies

Field studies, on the other hand, do not normally screen participants for characteristics that would make them ineligible for lab studies because participants in field studies are obtained in bars or drinking establishments and have consumed alcohol, presumably on their own volition, prior to taking part in the research study. Also, because participants have consumed alcohol on their own, obtaining participants with BACs higher than 0.08% is common. Overall, there are few differences between field and lab research with regard to the presentation of stimuli or measuring of dependent variables. One important difference, however, should be noted. Due to the fact that participants in field studies are intoxicated at the time when consent to participate is given, they must be provided with an opportunity to withdraw their participation at a later time (i.e., when they are sober).

Intoxicated Eyewitnesses: Experimental Findings

Researchers have been examining the effects of alcohol on eyewitness memory since the early 1990s. Early experiments examined the effects of alcohol on memory by comparing groups that were either sober or intoxicated at the time of encoding and then testing all participants on a different day when all participants were sober. The results from these studies suggested that intoxicated participants were less accurate when asked to recall the features of a target person and less accurate about describing the events that took place during the critical encoding period than were sober witnesses. However, participants who were intoxicated during encoding were just as accurate at identifying a target person in an identification task as witnesses who had not consumed alcohol. Although these studies were not specifically testing alcohol myopia theory, the results are consistent with alcohol myopia theory predictions.

Later research examined the effects of alcohol intoxication at the time of encoding and at the identification task. Although it is possible to conduct this research by having participants return to the lab a second time to become intoxicated again (i.e., context reinstatement), this body of research administered the dependent variables (e.g., a showup) relatively soon after the viewing of the target person and while the participants were still intoxicated. This research was unique from earlier studies in that it allowed researchers to study alcohol myopia theory by manipulating (a) the behavior of the investigator and (b) the identification procedure. This research was relevant to real police practice because the police often encounter intoxicated individuals in the course of their investigations and there had been no research on the potential vulnerabilities of intoxicated witnesses to police practices. The findings of these studies suggest that intoxicated participants are more susceptible to minor changes in police procedure, such as the instructions that are given to a witness prior to viewing a showup (e.g., “Please be careful when making your decision.”) and biased identification procedures (e.g., when the suspect is shown wearing similar clothes to those worn by the perpetrator). Ultimately, however, intoxicated witnesses could, under the circumstances of these research studies, be more accurate than sober witnesses. In addition, correct identification decision rates were in the neighborhood of 90%—a notably high rate even for sober witnesses in eyewitness identification research.

See also:

  • Accuracy of Eyewitness Descriptions
  • Eyewitness Memory
  • Best Practices in Identification Tests


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