Stress, Violence and Alcohol

Sharp End

• Police officers, military personnel and those in emergency response roles frequently respond dynamic challenging incidents

• Unlike bystanders, the role of ‘operational witnesses’ is to intervene, de-escalate and resolve

  • Increased likelihood of physical exertion and increased stress levels

Violent - Stress overview

• Stress meaning

  • Physiological response to stressor that is measurable by another party

  • Stressor must be perceived as negative

  • Stressed person must feel she has no control over the stressor

• Acute Stress (Important)

  • Short-lived

  • Triggers fight or flight response

  • Can be helpful by assisting focus or marshaling resources for a significant physical challenge

Violence - Effect of stress on memory

• emotionally arousing events are remembered better than neutral events (e.g., Payne et al., 2006)

  • neurobiological research suggests that stress hormones can enhance memory consolidation (McGaugh, 2000)

• BUT higher levels of stress disrupt hippocampus function and impair memory performance (Shackman et al.,2006)

• impaired memory likely reflects the level of stress and task complexity

  • Serious methodological issues in most eyewitness studies purporting to be about ‘stress’

• Optimal level of stress helps us to perform better but when it gets too high it can then hinder performance

Stress and Memory - Yerkes and Dodson curve (1908)

• slightly increasing stress actually helps us perform stress but it needs to be managed

• If a task is easy we can handle higher levels of stress before you burn out compared to harder task

Violence - SERE (Survival, Evasion, Resistance, Escape)

• Morgan et al., 2013

• Participants:

  • 861 active-duty military personnel

• Procedure Overview:

  • They were placed in a mock prisoner of war camp

  • After 12 hrs they were highly stressfully interrogated

    • Physical punishment, mental torture

  • After this they were exposed to stress of isolation, sleep and food deprivation for next 36hr

    • Exposed to misinformation in propaganda speech

    • Memory was then tested

• Results:

  • Memories for stressful events are also highly vulnerable to misinformation effect

    • false memory about non-trivial items (i.e., weapons) were observed in at least 27% of participants

    • higher errors, upwards of 80% of participants, of misinformation about uniforms or human faces

  • Majority of participants were correct when describing general characteristics about their interrogator (i.e. race, gender, height, build).

    • most participants were incorrect when describing more detailed characteristics (i.e., one's facial hair, eye color, or shape of face

  • show that despite any training it is a human feature to have fallibility in memory

Research gap: ‘operational witnesses’

• Eyewitness memory is usually tested under optimal encoding conditions (non-stressful)

  • Responding, acting or re-acting places additional demands on cognition

  • Training and experience of operational witnesses likely plays an important role

  • Understanding memory vulnerability in these contexts informs subsequent memory elicitation (e.g. interviewing)

Violence - exertion effects memory (Hope et al 2012)

• Serving Canadian police officers

  • Experimentally tested memory for a ‘live’ staged encounter with a hostile ‘suspect’

  • following a period of heavy exertion

• Results

  • Officers who had been physically exerted prior

    • Were less likely to identify the suspect in a lineup

      • only 27% correctly identified the suspect vs 54% in the control (no exertion) condition

    • Notably, no impairment in weapon detection

      • Arousal by competition – priorities processing risk items compared to the competition of other arousal topics

Violence - effect of arousal (Hope et al 2013)

• 300 UK Authorised Firearms Officers

  • Experimentally tested memory for a ‘live’ armed hostage scenario

  • Officers provided statements after incident

• Results

  • Accuracy rates were high for information

    • 93% accurate (range 83-100%)

  • But further analyses identified many gaps and omissions in the accounts provided

    • Suggests a performance trade off

    • Issues if this went to court and you missed stuff out

Effects of arousal and response role on memory - Hope, L. et al.  (2016)

• 80 serving Canadian police officers

  • Experimentally tested memory for a ‘live’ staged, escalating  encounter with an ‘armed suspect’

  • Officers took part on pairs, randomly assigned to ‘Active Responder’ or ‘Observer’ condition

• Results

  • Physiological arousals

    • The active officer was significantly more aroused

  • Free Recall

    • Significantly fewer correct details reposted by the active person than the observer

      • No difference in number of incorrect details

      • No difference in accuracy rates for Free Recall (high at ~96%)

  • Cued Recall

    • Overall performance

      • No differences in the total number of questions answered correctly or incorrectly

      • Overall, low accuracy rates (M = 57%)

  • Expectancy and Memory

    • 18% of officers reported that the perpetrator pointed a gun at them in the final phase of the scenario (in free recall) – never occurred in any scenario

How does alcohol affect memory

• Doesn’t effect accuracy just the amount of information given

• Alcohol and Witnesses

  • Strong link between alcohol and crime

  • Likely that many witnesses and victims will be under the influence when they witness a crime

Research - Ray & Bates, 2006

• Alcohol interferes with the transference of information from short- to long-term memory because it disturbs the encoding and consolidation

• During intoxication, encoding is more superficial due to a lack of rehearsal and other mnemonic strategies

Research - Perry et al., 2006

• sudden rise in blood alcohol concentrations (BACs) may produce fragmentary blackouts

  • This means that parts of the event(s) that took place during intoxication are not consolidated and not remembered afterwards.

Basic Alcohol research

• Perception that intoxicated witnesses are perceived as less reliable

• Basic research shows that intoxication decreases ability to

  • Maintain attention

  • Associate information with existing knowledge

  • Consolidate information into long-term memory

Intoxication - Field Study Van Oorsouw & Merckelbach, 2012

• Overview

  • 110 volunteers were recruited in local bars in Maastricht

  • 75 participants took part in follow‐up memory test

  • Within 3–5 days, participants were separately sent two memory tests

    • Free recall

    • Cued Recall

• Results

  • Both intoxication groups were less complete (i.e. reported less correct information) in their memories of the mock crime than the sober group.

  • Free recall accuracy did not appear to be affected by high intoxication levels.

Meta-analysis on effect of alcohol

• Alcohol has

  • Significant and moderate effect on number of correct details reported by mock witnesses

  • No significant effect on incorrect details reported

• Correct recall moderated by factors including:

  • Level of intoxication

  • Delay between encoding and retrieval

  • Type of questions asked (free recall versus cues recall)

Flowe et al (2019) - Alcohol and Fake Rape

• examined the effects of alcohol consumption and exposure to misleading postevent information on memory for a hypothetical interactive rape scenario

• 2 beverage (alcohol vs. tonic water) x 2 expectancy (told alcohol vs. told tonic) factorial design

• One week later, participants were exposed to a misleading postevent narrative and then recalled the scenario

• Participants who were told that they had consumed alcohol rather than tonic reported fewer correct details, but they were not more likely to report incorrect or misleading information

• Alcohol expectancy decreases the completeness of testimony but not its accuracy.

Effect of Cannabis - Vredeveldt et al. (2019)

• Field study in Amsterdam coffee shops (N = 120)

  • Participants viewed a videotaped criminal event, were interviewed about the event, and viewed a target-present or target-absent lineup.

• Witnesses under the influence of cannabis remembered

  • Fewer correct details about the witnessed event

  • No difference in incorrect recall.

  • Cannabis use was not significantly associated with lineup identification performance,

cannabis on eyewitness suggestibility - Kloft et al (2020)

• Examined effects of THC intoxication on susceptibility to false memory/suggestibility

  • Intoxicated participants showed the highest false memory rates in response to leading questions

  • vulnerable to suggestive questions while still under acute influence, but this effect disappeared at 1-week follow-up

Challenges for Interviewing

• Research shows that arousal/distraction, exertion and intoxication can negatively affect memory in applied contexts

  • Fewer correct details provided

  • Accuracy rate not necessarily affected

• Important for investigators to take encoding context (and witness state) into account