| Summary: | Understanding how movements are controlled is a difficult and elusive problem. Many different theories have been proposed but each has its faults and limitations, and so as yet, no unifying and comprehensive theory of action exists. This thesis is concerned with assessing a new theoretical perspective to see if it can improve our understanding. This theory, the τ-coupling theory, takes its philosophical basis from the ecological psychology movement. It is a psychological theory about perception-action couplings, and is formally stated in mathematical terms. It proposes how the closures of gaps are co-ordinated. In this thesis the plausibility and generality of the τ-coupling theory, and in particular the constant acceleration intrinsic τ-guide hypothesis, are assessed from three different perspectives. The first of these is in terms of oculomotor control. A comparison is made between the systems models and τ-coupling theory in the control of gaze shifting. The results suggest that the present formulations of systems models do not fully account for the behaviour observed, and a new model for gaze control, based on τ-coupling, is presented. The biological plausibility of this theory is further investigated in a study of the actions of AM, a patient with cerebellar damage. The data indicate that AM was able to τ-couple his movements onto a constant acceleration intrinsic τ-guide in certain situations which involved his actions to be controlled proprioceptively. However, in more complex situations, especially those involving vision, his τ-coupling ability was compromised. It is concluded that the cerebellum is involved in the use of visual information in τ-coupling. The extent to which the constant acceleration intrinsic τ-guide hypothesis can account for the control of a range of movements, and in particular reaching movements, was also assessed.
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