Obhi, Sukvinder Singh; (2003) Psychomotor combinations of action. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis is about psychomotor combinations of action. Psychomotor combinations of action relate to the different ways in which movements are put together. This idea is inspired by everyday life in which most of the actions we perform are combinations of various sub-components. A basic serial model of motor control is outlined which moves from stimulus identification (or the formation of an internal drive to move), via selection of a motor program to the eventual execution of that motor program. The model serves as a context in which to place the studies in the thesis. This thesis is divided into two parts, focussing on two different types of psychomotor combinations of action. The first part focuses on actions that are motorically identical but psychologically different and the second part is concerned with actions that are psychologically bound but motorically different. In order to investigate the former class of actions studies were conducted in which the motor output was held constant and the context in which this output is made was changed. Subjects made internally generated and externally triggered, but motorically identical actions in order to investigate this issue. In chapter 3, experiment 1 used measures of reaction time, and muscle activation (EMG) to examine externally triggered and internally generated actions and the control system(s) that produce them. It was found that internally generated actions exhibited greater levels of EMG activation than their externally triggered counterparts. In chapter 4, experiment 2, event related functional Magnetic Resonance Imaging was employed to investigate the neural systems underlying the production of actions that are motorically identical but psychologically different and how these systems might be related. Similar networks of brain activation were found for both internally generated and externally triggered actions. In addition, in a condition in which subjects prepared an internally generated action with the possibility of having to override their preparations in order to respond to an auditory tone, prefrontal areas were found to be active. To investigate actions that are bound at the psychological but different at the motor level, bimanual coordination tasks in which subjects were required to bind the different actions of the two hands together were employed. In such cases the psychological goal of the action is singular but the hands must perform different movements to achieve it. In chapters 5 and 6, experiments 3 and 4 employed the technique of repetitive transcranial magnetic stimulation to investigate the brain regions involved in the control and coordination of a bimanual coordination task. The SMA was found to be involved in the timing aspects of bimanual coordination. In chapter 7, experiment 5 examined the issue of motorically different but psychologically bound movements in a slightly different way by investigating the influence of perceptual and motor factors on the ability of subjects to produce coordinated movements. Motor factors were found to be more important than perceptual factors for coordination of discrete actions. The last chapter of the thesis summarises the results from the experiments reported and attempts to relate them back to the basic serial model of motor control proposed in chapter 1. The results are discussed in the light of relevant current knowledge in psychology and neuroscience.

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