Abstract
Our body clock, also known as the circadian rhythm, regulates alertness and activity levels across the day and determines periods of optimal cognitive performance. The exact timing of peak performance may vary due to inter-individual differences in the functioning of our body clock: Morning types perform best in the morning, whereas evening times reach their peak performance in the evening. This pattern is known as the synchrony effect. There are numerous benefits in scheduling cognitively demanding activities in congruence with individual performance patterns. Recall and recognition performance have been shown to be better at the optimal compared to the non-optimal hours of the day. However, the role of the synchrony effect in eyewitness memory performance received little attention in the literature.In the research programme presented in the current thesis, we aimed to investigate the effects of time-of-day optimality on memory performance in eyewitnesses. Across three single- and multi-session experimental studies, we (i) investigated the effect of time-of day optimality on accuracy and informativeness of free narratives and answers to cued questions about the mock crime (Chapter 1); (ii) explored time-of-day optimality effects on lineup identification performance and its postdictors (Chapters 1 and 2); (iii) tested time-of-day optimality effects in face recognition performance and memory for sources in which faces were encountered (Chapter 3), and (iii) explored possible synchrony effect patterns in the formation of false memories (Chapter 1). In Chapter 2 (N = 103), we tested whether matching individual time-of-day preferences can be beneficial for accuracy and informativeness of eyewitness reports, accuracy of eyewitness identification decisions and postdictive value of confidence and decision times. We also investigated whether time-of-day optimality affects the formation of false memories. Time-of-day optimality did not affect performance in eyewitness reports and false memory rates. Identification accuracy in target-present lineups was unexpectedly higher at non-optimal compared to the optimal time of day. Highly confident choosers were significantly better calibrated in their confidence judgments at non-optimal compared to optimal hours. Decision times were predictive of accuracy only at the optimal time of day.
In Chapter 3 (N = 324), we further investigated the possibility of the synchrony effectin identification accuracy and its posdictors. Results showed no significant differences in identification accuracy between optimal and non-optimal sessions. In line with findings reported in Chapter 3, confidence-accuracy relationship was stronger at the non-optimal time of day. Decision times were not predictive of accuracy.
In Chapter 4 (N = 91), we tested the possibility of synchrony effects in face recognition performance and ability to discriminate between the contexts in which faces were encountered. Results showed no benefit in overall face recognition performance. Participants showed no benefit from optimal testing in terms of their ability to exclude familiar but irrelevant faces. These findings are novel in demonstrating that face recognition performance is not subject to synchrony effect patterns commonly reported in the literature.
Overall, the results of our experiments show no evidence for the synchrony effect in any of the investigated aspects of eyewitness memory performance. It can be concluded that in healthy young adult eyewitnesses, circadian troughs in cognitive performance are not sufficient to result in significant reduction of evidential value of testimony, providing that other encoding and retrieval conditions were optimal. Our data suggest that eyewitnesses can take the presence of factors that impair cognitive performance into account and adjust their confidence judgments appropriately.
| Date of Award | Sept 2019 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Lorraine Hope (Supervisor), Melanie Sauerland (Supervisor) & Harald Merckelbach (Supervisor) |