| Summary: | The thesis explored the impact of personality on performance during category learning (CL) tasks, following motivational and reinforcing manipulations. In particular, the thesis explored how motivation and reinforcement affect performance during category learning tasks and, concurrently, the research aspired to clarify how reward sensitivity is modulated by individual differences in personality. According to findings which indicate that dopamine (DA) plays an important role in reward-based learning (Schultz, 1998; 2002), personality traits which may have a DAergic basis were considered. The thesis makes broad reference to the Reinforcement Sensitivity Theory (RST; Gray and McNaughton, 2000) and, in particular, to the Behavioural Activation System (BAS). Indeed, the BAS is believed to involve DAergic midbrain projections and be sensitive to rewards (Pickering and Gray, 2001). Therefore, the personality traits underlying the BAS are believed to have a DAergic nature and, subsequently, determine inter-individual variations in reward sensitivity. A series of behavioural experiments were conducted to explore the relationship between motivation and personality during CL tasks. Moreover, a biologically inspired model was developed to simulate the behavioural data and capture individual differences. The model had a DAergic basis that represented some of the biological mechanisms that underlie procedural learning and that may occur within brain structures thought to be part of the BAS (Gray, 1987). The model was shown to be a useful tool to obtain further insights into the experimental data. Impulsivity was found to mediate procedural learning in a series of studies. Thus according to RST (Gray, 1987), the present research shows that impulsivity might represent the underlying BAS trait. However, contrary to RST, the model indicated that inter-individual variations in procedural learning were dependent on individual's sensitivity to reward prediction error (RPE) signals rather than rewards per se. Finally, the model simulations suggest that category learning under asymmetric payoffs is mediated by both explicit and implicit (i.e. procedural) processes. The implications of these findings are discussed in light of personality theories and in relation to future studies.
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