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Abstract
Can a liar’s memory be trusted? Individuals in forensic settings are often motivated to lie, but to date, the vast majority of deception research has focused on the detection of deception, ignoring the possibility that lying may affect a liar’s memory for the truth. The few studies that have investigated this research question have been characterised by inconsistent methodologies, and perhaps as a result, conflicting findings have emerged. To fill this gap, the current thesis aimed to more systematically examine the effect of lying on an individual’s subsequent memory for both the original event and for their lies. First, by developing a methodology to overcome the limitations of previous research and second, by identifying potential mechanisms and boundary conditions underlying the effect of lying on memory.
To achieve these two aims, six experiments were conducted using three different experimental paradigms adapted from other areas of memory research. In each study, participants were exposed to a stimulus event before either responding truthfully, deceptively or not at all. Following a delay, individuals were tested for their genuine recall for the event. Across the six experiments, the effect of lying on memory was tested using different studied events (video footage, simple actions, mock crime), different methods of communicating the lie (written cued recall, verbal retrieval, face-to-face interview), different types of lies (self-generated lies, other-provided lies, stating the opposite of the truth), and different assessments of memory performance (free recall, cued recall, recognition, source monitoring tests).
Taken together, the research presented in this thesis suggests that deception can alter a liar’s memory. Specifically, liars exhibited impaired memory for the truth and also came to incorporate some of their own lies into their memory for the original event. However, the magnitude of these effects appears to be dependent on specific factors, such as retention interval, repetition, and type of lie. The findings of this research support the idea that lying is an effortful process which involves some rehearsal of the truth. The results also highlight the need for researchers and practitioners to consider the malleability of a liar’s memory in legal and clinical practice.