The evolutionary origins of executive functions : behavioural control in humans and chimpanzees
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Executive functions (EFs) are a set of cognitive operations, including working memory, inhibitory control and attention shifting, that underpin accurate, flexible and coordinated behaviour in many problem-solving contexts. While it seems likely that humans surpass nonhuman animals in EFs, previous research into the evolutionary origins of EFs is limited and lacks systematic comparisons of EFs in human and nonhuman animals. In this thesis, I aimed to overcome these limitations by developing a test battery to study EFs in our closest primate relative, the chimpanzee. Using an individual differences approach, I investigated the performance of 19 chimpanzees on several EF tasks and extracted two factors in an exploratory factor analysis accounting for 70.9 % of the variability. The two measures of working memory loaded onto one factor, suggesting that a common cognitive process underlay performance on both tasks. This factor could be clearly differentiated from a well-established measure of attention shifting, loading onto a second factor. In addition, the measures of inhibitory control did not contribute to a unique factor. Intriguingly, the emerging structure of separable EF processes, paralleled the EF structure suggested for human adults (Miyake et al, 2012). The subsequent comparison of a sub-sample of chimpanzees (n = 12; excluding aged individuals), pre-schoolers (n = 36) and undergraduates (n = 16) on two selected EF tests revealed impressive EF capacities of chimpanzees. Chimpanzees could deal with interference in working memory at levels comparable to four and five year-olds. Additionally, the ability of chimpanzees to shift attention was not significantly different from four year-olds; however, five- year-olds outperformed their primate relatives. My work suggests that important aspects of EFs are shared between humans and chimpanzees; while performance differences in EFs emerge late in human ontogeny. The implications of my results for theories on human cognitive evolution are discussed.
Thesis, PhD Doctor of Philosophy
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