Evaluating witness testimony: Juror knowledge, false memory, and the utility of evidence-based directions

AuthorRebecca K. Helm
Published date01 October 2021
Date01 October 2021
Subject MatterArticles
Evaluating witness testimony:
Juror knowledge, false memory,
and the utility of evidence-based
Rebecca K. Helm
University of Exeter, Exeter, UK
Eyewitness evidence is often important in criminal cases, but false or misleading eyewitness
evidence is known to be a leading cause of wrongful convictions. One explanation for mis-
takes that jurors are making when evaluating eyewitness evidence is their lack of accurate knowl-
edge relating to false memory. This article examines lay beliefs relating to memory and ways in
which they diverge from expert consensus. It identies ways in which current directions provided
to jurors in this area are likely to be decient in inuencing juror knowledge and in helping them
apply that knowledge in a case context, and develops criteria that can be used to assess the likely
effectiveness of directions. A new evidence-based training direction is designed based on these
criteria, and tested in a mock jury study (N=411). Results suggest that the proposed direction
is more effective than a basic direction in inuencing juror knowledge and facilitating the appli-
cation of that knowledge to case facts.
criminal procedure, legal directions, eyewitness memory, psychology and law, false memory.
Many modern common-law jurisdictions rely on lay juries to make determinations of fact in criminal
cases (Helm and Hans, 2019). In making these determinations jurors are frequently required to hear
and evaluate evidence from eyewitnesses to alleged crimes. Research suggests that jurors tend to rely
heavily on this evidence (Penrod and Cutler, 1999). Traditionally, juries have been left to make judg-
ments about the credibility of such evidence (including judgments of memory accuracy) without assist-
ance from experts. In one House of Lords judgment in England and Wales, Lord Hobhouse stated: The
courts should be cautious about admitting evidence from psychologists, however eminent, as to the cred-
ibility of witnesses. The assessment of the truth of verbal evidence, save in a very small number of excep-
tional circumstances, is a matter for the jury(R v Pendleton, 2002). This approach is designed to protect
Corresponding author:
Rebecca K. Helm, School of Law, University of Exeter, Exeter EX4 4QJ, UK.
E-mail: r.k.helm@exeter.ac.uk
Original Research Article
The International Journal of
Evidence & Proof
2021, Vol. 25(4) 264285
© The Author(s) 2021
Article reuse guidelines:
DOI: 10.1177/13657127 211031018
the independence of the jury and to avoid juror judgment being subsumed by expert judgment. It is based
on the assumption that jurors, as people themselves, have experience that makes them well-placed to
assess the credibility of other people (e.g. see JH and TG,A witnesss ability to remember events,
absent special considerations arising from the period of early childhood amnesia, will ordinarily be
well within the experience of jurors.)
However, research in both law and cognitive science shows that while laypeople do have their own
experiences of memory, they face predictable difculties when evaluating the memory of others.
These difculties are borne out in real casesin both the United States and United Kingdom, for
example, false or misleading eyewitness testimony has been identied as a leading cause of wrongful
conviction (National Registry of Exonerations, 2021; UK Miscarriages of Justice Registry, 2021, see
also Garrett, 2012; Wells et al., 2006). In many ways, these difculties are not surprising. Years of
research on memory in the behavioural sciences has shown that memory is highly complex, and that
accurately distinguishing true and false memory (i.e. true memory from apparent recollection of some-
thing that did not actually occur) is hugely challenging. In fact, even experts in controlled experiments
struggle to make such distinctions accurately (see, e.g., Ceci et al., 1994). The extent to which laypeople
have experienced, and are conscious of having experienced, false memory is also unclear. False memory
is not necessarily well within the experience of jurors.
Importantly for the jury system, research specically shows that laypeople hold beliefs about false
memory that are out of line with established and extensive empirical research that has been conducted
in the area. As a result, jurors are likely to be examining memory with a poor understanding of the
cues that suggest a memory could be false. Thus, jurors are likely to be making decisions that are
clearly at odds with conclusions that would be drawn on the basis of established research. For
example, in the case of R v Hallam, the appeals court noted that the eyewitness evidence upon which
the jury had relied in convicting the defendant was never very satisfactory(R v Hallam, 2012, para.
76). The fact jurors are provided with relatively little guidance when assessing memory makes it unsur-
prising that they make such mistakes, particularly when intuitive conceptions conict with established
knowledge in cognitive science. Presenting relevant information to jurors is likely to be helpful in this
regard, but care must be taken to ensure that such information is presented in a way that (1) appropriately
inuences juror knowledge, and (2) can helpfully inform (but not dictate) their applied judgments in the
context of a legal case. This paper focuses specically on how legal procedure can facilitate the presen-
tation of information in this way, specically in cases involving potential false memory.
The rst section of the paper examines likely discrepancies between layperson beliefs and empirical
ndings in the area of false memory in witnesses. The second part of the paper considers the extent to
which current procedure relating to testimony addresses these discrepancies, with a focus on procedure
in England and Wales. It suggests that to be effective in improving evaluations a direction must appro-
priately inuence juror knowledge and facilitate the application of that knowledge in a case context. It
then draws on psychological theory relating to memory and decision-making to show that current direc-
tions may be ineffective in both of these regards and to develop criteria for effective directions. The nal
part of the paper draws on these criteria to design and test an enhanced trainingdirection, compared to
no direction or a basic direction, in a mock jury experiment. The results suggest that giving jurors a more
detailed and evidence-based direction has the potential to minimise predictable weaknesses in their
decision-making, without substituting trial by jury for trial by expert.
Memory: Science versus public perception
Research over the last 40 to 50 years has provided extensive insight into the malleability of memory, showing
that memory is reconstructive. What is remembered is inuenced by a variety of factors including perception,
imagination, semantic memory, and beliefs (e.g. Brainerd and Reyna, 2005; Howe and Knott,2015; Loftus,
2003). Some of the ways that memory might be inuenced are relatively intuitive and thus within the
Helm 265

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