Abstract
Human behaviour is effect-oriented; we perform many different types of movements to obtain and respond to a variety of sensory consequences. In our everyday lives we have the experience of being in control of our movements and the sensory outcomes they elicit. This sense of agency, and the ability to initiate voluntary movements to obtain desired outcomes, originates from learning mechanisms that associate voluntary movements and sensory outcomes that often occur together. It is the anticipation of an outcome that allows for the selection of voluntary behaviour and the experience of control over movements and the outcomes they produce. Thus, movement heuristics that capture the predictive link between movement and outcome are necessary for voluntary behaviour and the sense of agency. Event-related potentials (ERPs) associated with outcome monitoring and evaluation, namely the feedback correct-related positivity (fCRP) and the P3, were examined in this thesis to investigate the cognitive processes mediating the formation of movement heuristics.
To differentiate learning a movement heuristic from previous movement-outcome learning paradigms that establish a simple one-to-one association between movement and outcome, a novel movement-learning task was developed. The task was designed so that multiple movements could elicit the desired sensory outcome, but learning of a movement heuristic depended on principal aspects common across all movements. This task and movement-related control tasks to isolate the learning component were initially tested in healthy controls. The ERP results demonstrated that the formation of a movement heuristic is the result of joint cognitive processes. Performance monitoring processes mediating the fCRP indicated the degree of movement-goal coupling, and the P3 indexed the evaluation of novel sensory information with regard to the preceding movement. It was proposed that the unique roles of the basal ganglia and the anterior cingulate cortex in the plasticity and consolidation, respectively, of movement-related information provided a potential outcome monitoring and evaluation system necessary for learning movement heuristics.
To elucidate whether dysfunction of basal ganglia signalling results in disruption of movement heuristic formation, and potentially altered outcome monitoring, a study was conducted with individuals with mild Parkinson’s disease (PD). In dopamine-medicated individuals with PD there was an overall enhancement in P3 amplitude. Additionally, the lack of difference in fCRP amplitude suggested an altered outcome monitoring. These results indicated that normal functioning of basal ganglia signalling might be necessary for the proper monitoring and evaluation of sensory outcomes.
Finally, the importance of outcome monitoring and evaluation to the sense of agency, were investigated using a judgment of agency task. Results from this study further emphasised the role of the fCRP as an index of movement-goal coupling, giving rise to the feeling to agency. Furthermore, the subsequent indication by the P3 that the sensory outcome was unanticipated swayed judgment to non-agency. By combining systematic manipulations of tasks along with investigations in a sample of neurologically impaired individuals, the present thesis has used a convergent approach to elucidate functional significance of the fCRP and the P3 in outcome monitoring and evaluation.