Eye spy a liar: the effect of deception on fixation-based measures of memory

The over-arching aim of this thesis was to evaluate a new experimental approach to detect recognition memory in liars, when recognition of familiar photographs was intentionally concealed. Eye tracking was selected as a novel methodological approach to memory detection because previous eye movement research documented that recognition of familiar faces and scenes produced fewer fixations to fewer regions of longer durations. The effect of deception on fixation-based measures of memory was examined in four experimental chapters. Experiment 1 explored whether fixations exposed concealed person recognition of three different familiar face types: newly learned via one exposure, famous celebrities, and personally known. Multiple fixation measures exposed recognition when liars denied recognition of famous celebrities and people who were personally known. Memory for newly learned faces was revealed during honest recognition solely in fewer fixations, with a trend in the number of fixations to suggest memory in lie trials. Experiment 2 emphasised monitoring of memory and eye movements during a similar concealed recognition task. Participants told the truth and lied about faces that were newly learned-to-criterion and personally familiar faces followed by a confidence rating (0-100%) based on each honest and deceptive recognition judgement. Effects of memory were observed in multiple fixation quantity measures and in fixation durations. The pattern of results for newly learned faces was the opposite of results found in Experiment 1. Unexpectedly, no effects of memory were found during honest recognition of newly learned faces, but fewer fixations and run counts were observed during lie trials. The data suggest that the clear reduction in viewing during lie trials could be a consequence of participant’s efforts to control their gaze behaviour to evade detection combined with recollective efforts to remember then conceal newly learned faces. Experiment 3 monitored fixations during concealed recognition of objects and scenes. When participants told the truth about personally familiar scenes and buildings memory effects were observed in fewer fixations, run counts and interest areas visited. During lie trials, effects of memory were only robust for the number of fixations. Similar to Experiment 2, lies about items newly learned-to-criterion produced no effect of memory in truth trials but revealed fewer fixations, run counts and areas of interest visited during lies. In both Experiments 2 and 3, a reduction in the variability of verbal confidence ratings was associated with recognition of personally familiar faces. Experiment 4 monitored fixations whilst participants viewed pairs of faces associated with specific scenes. The location and duration of first fixations revealed a preference for viewing faces that matched the scene displayed. Longer fixation durations in the last fixation also indicated deceptive efforts when intentionally making misidentifications. Overall, the results of the present thesis supported the potential of fixations as markers of memory when people lied about recognition of faces, scenes, and objects, as well as face-scene relationships. The results suggest that memory effects during recognition of personally known faces is robust in the number of fixation measure, but is observed in less fixations measures during lies about recognition of personally familiar objects and scenes. Furthermore, memory effects during recognition of newly learned items is more vulnerable to cognitive load and other executive processes, such as trying to control eye movements, and thus caution is advised when interpreting the effect of memory on fixations during concealed recognition of newly learned items. The research recommends that future experiments carefully explore the ability of liars to effect countermeasures on gaze behaviour to evade memory detection. The research further suggests that fixations durations might be a better measure to distinguish lies from truths about recognition and that the combined effect of memory and cognitive effort during lies produce more consistent and distinguishable differences in fixation durations between truth tellers and liars.