It’s all in the detail
: examining verbal differences between children’s true and false reports using cognitive lie detection techniques

  • Hannah Cassidy

Student thesis: Doctoral Thesis


Police interviewers require a new investigative interviewing tool to facilitate the discrimination between children’s true and false reports. This thesis investigated whether cognitive lie detection techniques could fill this gap in current practice. Chapter 1 introduces the cognitive lie detection paradigm, highlighting the lack of research within the child deception literature and the paradigm’s potential as a means for detecting deceit in children. Chapter 2 explores imposing cognitive load through the use of gaze maintenance to exaggerate differences between child truth-tellers and child lie-tellers. In Experiment 1, maintaining gaze (either with the interviewer’s face or a teddy bear’s face) resulted in truth-tellers providing significantly more detailed reports than lie-tellers. This finding was not apparent for the control condition where children were given no gaze instruction. In Experiment 2, this exaggerated difference between the accounts of the truth- and lie-tellers facilitated deception detection when the children were instructed to look at interviewer’s face, but not at the teddy bear’s face. Poor discrimination for the latter group was discussed with regard to the gaze behaviour of the children being regarded as ‘fishy’ by the evaluators. Chapter 3 investigates whether playing an example of a detailed free recall provided by a peer (referred to as another child’s model statement, AMS) elicits longer statements that contain more cues to deceit in an eyewitness context than when no model statement is used. Both child truth-tellers and child lie-tellers provided more details and more new information following AMS. However, truth-teller accuracy decreased. In Chapter 4, interview clips from Chapter 3 were judged by adult evaluators who found it difficult to differentiate between children’s true and false reports. This could be a consequence of quantity of detail not being a reliable indicator of veracity for this sample of interviews. Chapter 5 tests the use of children’s practice interviews as their own model statements (OMS) compared to AMS and having no model statement (NMS). Only AMS encouraged children to include more details and more new information in their post-model statement true and false reports. Further research is required to understand the socio-cognitive mechanisms that create this behavioural difference. Chapter 6 describes a field study that presented the cognitive lie detection techniques investigated in the previous chapters to police officers who interview child witnesses regularly. Of all the techniques, OMS was considered to be the most viable option, although police officers suggested that all of the interview techniques would require adaptation for use in the real world. The practitioners provided an insightful look at the current child-interviewing context in the UK, which provides a basic framework that could be considered when designing child deception detection strategies in the future. Finally, Chapter 7 summarises the main findings of this doctoral thesis, discusses their theoretical and practical implications, and puts forward ideas for future research.
Date of AwardNov 2016
Original languageEnglish
Awarding Institution
  • University of Portsmouth
SupervisorLucy Akehurst (Supervisor), Julie Cherryman (Supervisor) & Aldert Vrij (Supervisor)

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