Browsing Faculty of Social Science by Subjects
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Between-task consistency, temporal stability and the role of posture in simple reach and fishing hand preference in chimpanzees (Pan troglodytes)Studying hand preferences in chimpanzees can provide insights into the evolutionary origins of human hemispheric specialization. Research on chimpanzee hand preference requires careful examination of important factors such as posture, between-task consistency and temporal stability, although few studies have investigated all of these factors in combination. We investigated hand preference in simple reach and fishing behaviours in a group of 19 chimpanzees at Chester Zoo in the UK. Simple reach was defined as extending a hand to grasp a small object, then flexing the limb in a continuous motion, and was examined in quadrupedal, sitting and climbing postures. Fish in hole was defined as inserting a stick into a hole in the wall with one hand and then extracting it with the same hand. Between-task consistency of hand preference was assessed by comparing simple reach and fish in hole, while temporal stability was assessed by comparing simple reach from two points in time: 2017 and 2019. The data showed no significant influence of posture on the strength of hand preference, which contrasts with previous research. The findings of this study show temporal stability in simple reach, although only partial between-task consistency. Overall, the results indicate that simple reach elicits laterality at the individual level and is consistent across postures and stable over time, which is consistent with the literature. These results suggest that posture stability may be important in affecting hand preference. Further, whilst there was overall stability in hand preference across time periods, some individuals changed their preferred hand, suggesting there may be individual level temporal instability of hand preference for certain tasks.
Laterality in Chimpanzees: Links with Behavioural Style and Social NetworksThis thesis presents a series of studies investigating laterality in chimpanzees and its links with personality examined as behavioural style and social networks. The studies presented in this work were conducted by observing a group of 19 chimpanzees in captivity and present new findings in this species. However, this thesis has a broad evolutionary perspective, addressing important questions regarding personality and laterality that could prove helpful to the understanding of the evolution of laterality in vertebrates. Chapter 1 offers a general review of the three main areas of knowledge investigated: laterality, animal personality and primate social networks. Then, the first study of this project, presented in Chapter 2, began by exploring hand preference in the chimpanzee group, investigating spontaneous actions and unimanual tasks and expanding previous research by studying posture, between-task consistency and temporal stability. Chapter 3 investigated additional measures of motor laterality and proposed a novel way of measuring laterality in primates. Together, Chapters 2 and 3 directly examine laterality in chimpanzees and serve as the base from which to explore the links between laterality, personality and social networks in the subsequent studies. If lateralization is rooted in emotional processing and hemispheric lateralization, then individual differences in behaviour (particularly those that reflect emotional expression) would show a relationship with individual laterality. In order to address this question, Chapter 4 studies behavioural style in chimpanzees and its possible link with laterality. Simultaneously, if intraspecific coordination plays a role in the development of population level laterality, similarly lateralised individuals would likely have strong bonds to coordinate with each other. Chapter 5 introduces the approach and techniques of social network analysis and uses them to explore and describe the social structure of the group while describing the integration of a new adult chimpanzee. Chapter 6 applies social network analysis to explore if laterality plays a role in the way the group is structured. Lastly, Chapter 7 integrates all empirical chapters and presents the final discussion and conclusions of the thesis.
Right-lateralized unconscious, but not conscious, processing of affective environmental soundsMuch research on the laterality of affective auditory stimuli features emotional speech. However, environmental sounds can also carry affective information, but their lateralized processing for affect has been studied much less. We studied this in 2 experiments. In Experiment 1 we explored whether the detection of affective environmental sounds (from International Affective Digital Sounds) that appeared in auditory scenes was lateralized. While we found that negative targets were detected more rapidly, detection latencies were the same on the left and right. In Experiment 2 we examined whether conscious appraisal of the stimulus was needed for lateralization patterns to emerge, and asked participants to rate the stimuli's pleasantness in a dichotic listening test. This showed that when positive/negative environmental sounds were in the attended to-be-rated channel, ratings were the same regardless of laterality. However, when participants rated neutral stimuli and the unattended channel was positive/negative, the valence of the unattended channel affected the neutral ratings more strongly with left ear (right hemisphere, RH) processing of the affective sound. We link our findings to previous work that suggests that the RH may specialize in the unconscious processing of emotion via subcortical routes.