Evaluating the origins of the preferred hand and manual performance asymmetries in unimanual and bimanual tasks across the lifespan

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The preference to perform most unimanual tasks with one hand is an intriguing human characteristic. One notable aspect of hand preference is that certain tasks tend to produce stronger preferences and greater selection of the preferred hand than other tasks. Likewise, the magnitude of the preferred-hand advantage depends heavily on the task examined (McManus, van Horn & Bryden, 2016). One often cited explanation is that the degree of skill required to perform a particular task may drive hand selection, which then allows the preferred hand to become more adept at those highly skilled tasks (Steenhuis & Bryden, 1989). In reviews of our work(46, 6, 31) we have argued that "skilled behaviour" may not adequately explain handedness. Work remains to determine the nature of what each limb/hemisphere system is specialized for with respect to limb selection and performance abilities. The proposed research will elucidate the nature of what each limb/hemisphere system is specialized for with respect to limb selection and performance abilities in both unimanual and bimanual tasks. An emphasis will be placed on understanding the performance abilities of the non-preferred limb and left-handed individuals, both of which have been overlooked in past research. Importantly this work will also examine changes in limb selection and performance abilities across different age groups, from children to seniors. The long-term objective is thus to create a lifespan model of the maturation of motor lateralization that better explains the myriad of contradictory findings in unimanual and bimanual tasks. Short-term objectives will be to examine: a) limb selection in both unimanual and bimanual tasks (Research Theme D1); b) the relative abilities of each hand in unimanual and bimanual tasks (Research Theme D2); and c) maturation in lateral preference and performance in both unimanual and bimanual tasks (Research Theme D3). To further tease apart the nature of what each limb/hemisphere system is specialized for we will explore lateral preference and performance in both unimanual and bimanual tasks in; d) left handers (Research Theme D4); e) individuals with impaired motor planning/execution (e.g. autism spectrum disorder, ADHD) (Research Theme D5). While handedness and lateralization of motor function have been studied in the past, there are large gaps in our understanding of what each limb/hemisphere system is specialized for with respect to limb selection and performance abilities. Unfortunately, many studies include only young adults or only right-handed individuals, thus not capturing the complete picture of lateral preference, selection, and performance abilities. The proposed research will fill several gaps in current theories, inform researchers regarding the metrics of handedness, and be applied to aspects of education, industry, and training.