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Jeffrey Gray's (1973, 1981, 1991) Reinforcement Sensitivity Theory (RST) of motivation and learning comprises a Behavioural Activation System (BAS) and a Behavioural Inhibition System (BIS), and concerns their relationship to personality, mood, and psychological disorders. The BAS, which mediates responses to reward and relief, is thought to provide a causal basis for Impulsivity (Gray, Owen, Davis, & Tsaltas, 1983). While the influence of this perspective has been formidable, the original connection between the BAS and Impulsivity was speculative (Diaz & Pickering, 1993; Gray et al., 1983) and evidence from a wide variety of research domains has begun to converge upon the possibility that Impulsivity and BAS-reactivity are divergent constructs (e.g., Dawe & Loxton, 2004; Depue & Collins, 1999; Pickering, in press; Quilty & Oakman, 2004). Following on from this research, the present thesis attempts to provide a comprehensive evaluation of the putative correspondence between BAS-reactivity and trait Impulsivity. In Study1, rewards and punishments were delivered using a two-alternative forced-choice vignette task. It was found that all three BAS measures from Carver and White's (1994) BIS/BAS scales predicted the development of a preference for the rewarded response. Two out of three measures providing typical conceptualisations of trait Impulsivity were not significant predictors. One Impulsivity scale did, however, predict response-bias in the same manner as the BAS scales. Post hoc analyses suggested that this may be due to the scale having a partial basis in concepts relevant to reward motivation, and that further validation of this scale may be required. In Study 2, the three successful BAS measures from Study I were examined in terms of factor structure and concurrent validity. Factor analysis suggested that Carver and White's (1994) Drive, Fun, and Reward-Responsiveness scales are distinct constructs. Multivariate Regression was then used to construct two composite variables, one from various measures of Impulsivity, and one from various measures of BAS. Both Drive and Reward-Responsiveness were significant predictors of BAS but did not predict Impulsivity. Fun was a significant predictor of both composite variables. These results suggest that there is a distinction between BAS and Impulsivity, but that some measures are likely to reflect mixtures of the two constructs. Studies 3 and 4 examine Dickman's (1990) measures of Functional and Dysfunctional Impulsivity, which appear to capture the distinction made in this thesis between BAS and Impulsivity. In Study 3, correlation and factor analysis showed that Functional Impulsivity was strongly related to measures of BAS but also negatively to measures of BIS. From a joint-effects view of RST (e.g., Corr, 2001; Pickering, 1997), this is what might be expected of a measure of reward-reactivity. Dysfunctional Impulsivity, in comparison, had a somewhat different overlap with other personality measures, and was most strongly associated with Psychoticism and measures of Impulsivity. In Study 4, Functional and Dysfunctional Impulsivity were compared, along with two other measures of BAS, in the prediction of response-bias using a very similar experiment to Study I. Results showed that Functional Impulsivity and both BAS measures predicted a preference for the rewarded response. Dysfunctional Impulsivity appeared to predict insensitivity to reinforcement- higher scorers on this scale had the same response-bias under punishment as they did under reward. In Studies 5 and 6, a new measure of BAS was evaluated (the Appetitive Motivation scale). The specific aim was to provide a measure of BAS which was explicitly designed not to have a basis in concepts central to Impulsivity. In Study 5, initial psychometric properties of the Appetitive Motivation scale were reported, along with concurrent relationships with other individual differences measures. Results showed it to be strongly correlated with other measures of BAS and various broad- and narrow-focus measures of Extraversion. Most measures of BAS showed similar relationships with other scales, while measures of Impulsivity tended to be most strongly related to Psychoticism. In Study 6, a response latency task was devised to provide operations of reward-reactivity. The new Appetitive Motivation scale and one other BAS measure predicted experimental criteria (an additional BAS measure was not predictive). Results broadly suggest that the new scale is a promising measure of BAS, and the implication seems to be that Impulsivity is not central to the concept of reward-reactivity. Overall, the balance of evidence appears to favour the hypothesis that trait Impulsivity and BAS/reward-reactivity are conceptually distinct. This is a significant conclusion, and argues that a central tenet of Gray's theory of personality requires clarification. Implications of this research for the understanding of personality are discussed, and future directions for investigation are suggested.
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