6.1.7 – Factors influencing eye-witness testimony, including consideration of reliability (including post-event information and weapon focus).

Stress (Arousal)

Yerkes-Dodson Law

Yerkes-Dodson Law


When witnessing a crime, eye-witnesses are often under a lot of stress. The Yerkes-Dodson Law (1908) states that we reach an optimal point of stress in terms of recalling information. No stress means we won’t remember well, but too much stress will have the same effect. Often when witnessing a crime, we are under too much stress which reduces recall.


(+) Valentine and Mesout (2009)
(-) Recall in articifial situations can also be accurate, despite the low arousal.
(-) There is contradicting evidence to suggest that it applies in field studies of eye-witness testimony of realistic events. (Yuille and Cutshall (1986) – the greater the arousal, the more accurate the recall)

Post-Event Information


Experiences after the event can impact the memory of the event. This is common because they often have lots of time between witnessing the event and recalling it in an interview or in a trial. For example, they may see information on the news, from other people, etc.

Reconstructive memory states that when we recall information, we mix our knowledge of what happened and our expectations of the event (Schemas built from cultural norms, for example). Therefore, we usually recall the main facts of the situation but the rest of the recall is influenced by our reconstruction.

Lots of the evidence for this comes from Loftus. It has been found that exposure to misleading post-event information leads to inaccurate recall (accuracy often falling below levels of chance (Loftus et al., 1978)).

Leading questions are a source of post-event information and can affect accuracy of recall. They can be asked at police interviews and trials. They may be unintentional or intentional, as they can be used to influence the answer and may be used by lawyers in an attempt to get a non-guilty verdict for their defendent.


(+) Loftus & Palmer (1974) – Leading questions do affect eye witness testimony.
(-) Yuille and Cutshall (1986) – Leading question do not affect eye witness testimony.

  • However, only a small sample was used, so participant variables could have had an impact.
  • Field study –> higher ecological validity.

(-) Most of the research focuses on specific facts and very little exists with open ended questions, which is a more ecologically valid way of researching this.
(-) Most of the research is lab-based and therefore lacks ecological validity. This means that it doesn’t consider stress levels whch seem to have a large impact.

Weapon Focus


If there is a weapon present during the crime, this tends to decrease the accuracy of eye-witness testimony. This could be explained in two ways:


The presence of a weapon increases the stress of the situation. This could lead to them reaching the optimum stress level for recall (Yerkes-Dodson Law). This could, however, lead to them remembering a lot about the weapon. If the weapon causes them to stress too much, it could lead them to not remember much about the situation


In most parts of the world (The notable exception being some parts of the USA), seeing a weapon is unusual. This means you will draw your attention and focus on the weapon more than the surroundings. This can lead to less accurate recall because you might not focus as much on the perpetrators’ face, for example.


(+) Loftus et al (1987) – Weapon focus occurs because it draws the witness’ attention away from other important details.
(+) Pickel (1998) – It’s the unusualness of the gun which causes the decrease in accuracy, as it makes you pay more attention to it. It’s not the threat.
(+) Pickel (2006) – With correct training, they found that it is possible to overcome weapon focus.
(-) Wagstaff et al. (2003) – The presence of a weapon had no effect on accuracy of recall.