OVERVIEW OF VARIABLES KNOWN TO AFFECT EYEWITNESS TESTIMONY

• Jurisdiction: Australia

Variables ........................................................................................................ [65.300]

Prior knowledge, biases and expectations ................................................... [65.310]

Attention to, and processing of, target information ....................................... 65.320]

Distinctiveness and salience of event details ............................................... [65.330]

Related or competing information ................................................................. [65.340]

Social compliance and motivation ................................................................ [65.350]

Presence of stress or trauma at the time of the event ................................. [65.360]

The interval between the crime and the retrieval test .................................. [65.370]

Age of the witness (chronological and mental age) ..................................... [65.380]

Individual difference factors .......................................................................... [65.390]

Summary ....................................................................................................... [65.400]

[65.300] Variables

In this section, we provide a brief overview of the variables, or groups of variables, that have been measured in scientific research and subsequently shown to affect witnesses' susceptibility to error when testifying about events. These variables are influential because they affect eyewitnesses' ability to (a) perceive, encode, retain or retrieve target event information; (b) make distinctions between information genuinely acquired at the event or acquired later from other sources; and/or (c) share what they know about the target event. We describe these variables under several broad headings, which include prior knowledge, biases and expectations; attention to, and processing of, target information; distinctiveness and salience of event details; related or competing information; social compliance and motivation; presence of stress or trauma at the time of the event; and the interval between the crime and the retrieval test. These factors impact all witnesses in similar ways. Even though our examples are mostly drawn from studies using adult witnesses, the general principles or conclusions stated throughout these subsections are able to be generalised across child and adult participant groups.

The remaining two sections, entitled "age of the witness" and "individual difference factors", discuss how eyewitness testimony performance varies across different stages of the lifespan and in accordance with individual demographic, internal and background factors.

[65.310] Prior knowledge, biases and expectations

People's cognitive systems organise knowledge and prior experience in order to facilitate later perception, thinking, comprehension, remembering and problem solving. Such organisational systems are often referred to by scientists as schemas. Specific schemas are selected by people in specific circumstances (based on prior knowledge and experiences) to work out what is happening and what will happen shortly. These expectations or schemas, in turn, influence how events are perceived and remembered. A classic experiment illustrates this point well with regard to event memory. Specifically, Bransford and Johnson (1972) asked a group of adults to listen to the following passage of text.

The procedure is actually quite simple. First you arrange things into different groups depending on their makeup. Of course, one pile may be sufficient depending on how much there is to do. If you have to go somewhere else due to lack of facilities, that is the next step; otherwise you are pretty well set. It is better to do too few things at once than too many. Remember mistakes can be expensive. At first the whole procedure will seem quite complicated. Soon, however, it will become just another fact of life.

Afterwards, when examined on what they remembered, the people who heard the passage demonstrated very low comprehension and remembered little of it. By contrast, a group of adults who heard the same passage but were initially told it was called "washing clothes" demonstrated relatively high comprehension and recalled the information well. The benefit of providing the context (washing clothes) is that it led the people to draw on their knowledge and expectations about the topic - by selecting that schema - to create a framework that helped them to understand the passage and improve their memory of it later.

Having an event schema, however, does not always facilitate accurate recall. The same cognitive mechanisms that led to improved memory for the "washing clothes" passage can also lead people to misinterpret events as they unfold, and to misremember event details that are irrelevant to (or inconsistent with) personal biases and expectations. Witnesses cannot take in all available information during an event; thus, they must sometimes "fill in" the gaps with information typical of a particular experience - what scientists call "schema-consistent" information (Alba and Hasher (1983)). Many studies have illustrated this effect, including studies which have focused on details of events (Hannigan and Reinitz (2001); Kleider, Pezdek, Goldinger and Kirk (2008); Loftus et al (1978)). For example, Tuckey and Brewer (2003) asked a group of adults to watch a film of two people robbing a bank. In some versions of the film, the scenes were ambiguous (a robber pointing a bag as if it contained a gun), while in others they were unambiguous (the robber held a bag by his side, which clearly could not have been a gun). Later, when the people were interviewed, they were more likely to report seeing a gun when they saw the ambiguous version of the film than the non-ambiguous version.

Even experiences, beliefs and expectations about how we should remember certain events can contaminate verbal and written recollections of these events or lead to incorrect judgments about the timing of the events. For example, adults often expect old memories to have relatively weak perceptual details; thus, if recollections are vivid and detailed, it is assumed they are recent even if there is no actual memory of when the details occurred (Friedman (2004)). Adults also expect their memories to be worse when intoxicated, and this can affect their recollections of events, according to a study by Assefi and Garry (2003). They found that adults who thought they were intoxicated on vodka (but had merely been given a non-alcoholic substance) made more errors on a memory task than the group who knew they were not intoxicated.

Event schemas or stereotypes can heighten a person's susceptibility to believing false information. This is particularly true when the misleading information is consistent with the schema or stereotype (Leichtman and Ceci (1995); Loftus et al (1978); Roberts and Powell (2006)). Further, interpretations about the plausibility of information (based on prior knowledge and expectations) play a critical role in the creation of false memories. To develop a false belief, a person needs to accept the false information as being true (which is more prevalent when the information is plausible). Plausibility can grow into beliefs, and beliefs, in turn, can grow into false memories via reinterpretation of false information (narratives or images about the event) into genuine memories (Sharman, Garry and Hunt (2005); Strange,

Sutherland and Garry (2006)).

Scientists have also demonstrated that it is relatively easy to "implant" memories of false (even highly implausible) events, including being (a) an infant in a crib and watching a mobile over the bed; (b) bullied; (c) a witness to a demonic possession; (d) the victim of a vicious animal attack; and (e) a rider in a hot air balloon (see Lynn et al (2014) for a brief review). In a mega-analysis comprising 423 memory reports, 30 per cent of people were classified as having developed false memories, and an additional 23 per cent had "accepted the event to some degree" (Scoboria et al (2017)). In another example, 26-30 per cent of people developed detailed memories of committing a crime serious enough to warrant contact with the police (Shaw and Porter (2015); see Wade, Garry and Pezdek (2018) for the reanalysis). Most of these false memories involved assaulting another person, sometimes with a weapon. It is remarkable that people would come to remember, falsely, having committed a crime serious enough to interfere with (say) job prospects or international travel.

[65.320] Attention to, and processing of, target information

All things being equal, the time spent processing event detail at the time of encoding affects the accuracy and detail of witness testimony. Exposure time of target information is related to memory such that the longer the time period for which a target detail is observed, the more people will pay attention to it and, subsequently, the more information they will remember about it (Bugelski (1962); Laughery, Alexander and Lane (1971)). This phenomenon is consistent with research on facial recognition performance, which is generally superior with longer exposure durations (Ellis, Davies and Shepherd (1977); MacLin, MacLin and Malpass (2001); Memon, Hope and Bull (2003); Shapiro and Penrod (1986); Weber and Brewer (2004)). The phenomenon is also consistent with research on the effect of event repetition on witness recall. After multiple occurrences of an event, more frequently occurring details are better remembered over time and are more resistant to false interviewer suggestion compared to details that were experienced fewer times (Powell and Thomson (1996); Powell, Roberts, Ceci and Hembrooke (1999)).

More time spent attending to target information does not necessarily translate into better remembering. The physical (eg, lighting, sound) conditions, and the distance between the person and any observed event, need to be...