Walsh, E; (2008) Exploring the cognitive precursors of movement using a sensory-detection task. Doctoral thesis , UCL (University College London).

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Abstract

Movement-related sensory suppression is an example of a motor-sensory interaction whereby sensory stimuli are perceived as less intense before and during a movement than at rest. This thesis focuses on sensory suppression of a weak electrocutaneous stimulus delivered just prior to movement onset, and develops this situation as a paradigm for studying motor-sensory interactions. In a typical experiment, subjects prepared a motor response in advance of a visual signal. They received a weak electric shock to the right hand just prior to voluntary movement. Subjects reported at the end of each trial whether they detected the shock or not. Movement-related sensory suppression was measured by comparing shock detection rates with non-movement control trials. This general paradigm was then used in a series of behavioural experiments which systematically manipulated cognitive processing prior to movement. Premovement suppression was used to investigate the cognitive precursors of movement. First, it was shown that sensory suppression occurred for actions which were prepared, but then inhibited before execution. Second, sensory suppression was combined with the classic "stop-signal" paradigm. On trials where a stop signal came too late for subjects to inhibit their movement, a brief period of release from sensory suppression was nevertheless observed, as if the movement had been cancelled. This brief independence of sensory and motor systems suggests that the balance of excitation-inhibition is set separately for each system. Third, when subjects performed pre-prepared sequences of movements, premovement sensory suppression was related only to the first movement in the sequence, and not to subsequent movements. This suggests that motor-sensory interactions are programmed at the level of individual movements, not sequences. Finally, delivery of an unexpected startling auditory stimulus produced an acceleration of sensory suppression corresponding to the well-known acceleration of motor reaction time. This finding suggests that subcortical motor circuits involved in startle may also contribute to sensory suppression. Overall, sensory suppression proved a useful tool for investigating the cognitive processes that take place prior to movement.

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