| Summary: | Many everyday tasks involve multiple movements that require accurate and proficient motor control (e.g., typing on a keyboard, using a smart phone or tablet, placing a pen in a desk organiser or simply making a cup of tea). Researchers have adopted many approaches to understanding how these type of aiming movements in order to examine how they are prepared and executed. In fact as early as the 19th century researchers were investigating the control of rapid target direct movements (Woodworth, 1899) and revealed that single target actions consist of at least two distinct components; the first is the initial impulse and assumed to be fast, ballistic, pre programmed movement designed to bring the limb into the vicinity of the target; the second is an error correction phase whereby vision (or proprioception) of the limb and target are used to make corrections to the limb trajectory in order to accurately reach the target. This notion of a two component model is still consistent with recent motor learning perspectives, which also point to a two-component with multiple processes model of goal-directed aiming (for a review, see Elliott et al., 2010). Studies have found that rapid aimed hand movements take longer when the movement is directed at a second target rather than executed toward a single target (Adam et al., 2000; Chamberlin & Magill, 1989; Elliot, Helsen, & Chua, 2001; Lavrysen, Helsen, Elliott & Adam, 2002). This phenomenon is known as the 'one-target advantage' (OTA), the prominent explanations of which fall in one of three hypotheses; online programming (Chamberlain & Magill, 1989); movement constraint (Fischman & Reeve, 1992); movement integration (Adam et aI., 2000). All three of these hypotheses adopt the notion of central programming and online processes in attempts to explain why and how movements within a two target aiming task are functionally dependent. It has been suggested that the dependency/movement integration between segments is aided by the availability of vision (Helsen, Adam, Elliott, & Beukers, 2001) through the visual monitoring and regulation of actions (also see Khan , Lawrence, Franks, & Buckolz, 2006). In direct support for this is found in conditions where visual feedback is occluded, since participants have been reported take longer to initiate their movement (Lavrysen et al., 2002); presumably this increase in reaction time is to ensure that actions are accurate and can be integrated without the use of visual information. In light of the above, an issue with has been at the forefront of much theorising is the extent to which movement integration is dependent on the relative contributions of central planning and online processing together with the role that vision might take in this interplay. 1.2 Outline of the thesis This thesis utilises a series of experiments in an attempt to investigate issues relating to the planning and control of multiple target actions under vision and no vision conditions. The first experiment focused on the movement variability or the accuracy equivalent of the OTA. The aim here was to investigate the role of visual feedback in the interaction between movement segments within a time constrained action. This allowed a more direct approach to testing the MCH and MIH hypotheses than previous research that have adopted paradigms where movement times that are free to vary. Over the course of3 further investigations, the use of visual feedback in the interplay between planning and online integration was examined under full vision conditions and conditions where visual feedback was occluded at the end of the first movement. Here movement times were free to vary and the primary purpose"was to investigate the effect of varying the location of the first target location under a non-perturbed (investigation 1) and unexpected perturbation (investigation 2) paradigms together with the effect of unexpectedly perturbing the location of the second target (investigation 3). The explanations of the OT A are both expanded and re-examined in light of the role of visual information plays in the integration between movement segments. 1.3 Thesis Format This thesis consists of a review of the literature, four research papers and general discussion. All four manuscripts are written as standalone research articles. The first manuscript has been published in the international psychology and motor control journal Acta Psychologica. The remaining manuscripts are currently in preparation for publication consideration. For consistency, all manuscripts are written in style adopted by the school of Sport, Health and Exercise Science, Bangor University, which is described in American Psychology Association Publication Manual 2009 (6th Edition) and current recommendations of the Bangor University for thesis preparation. For the same reason, all citations are included a single section and the end of this thesis and illustrations are numbered consecutively.
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