It is increasingly recognised that affect plays a crucial role in decision making. This thesis investigates the extent to which arousal is an important, and neglected, factor in decision making under risk. Arousal level was manipulated on two gambling tasks via (1) muscle-tension-induced (MTI) arousal and (2) increased magnitude (and quality) of monetary reinforcement. On the Iowa
Gambling Task (IGT), a commonly used neuropsychological tool involving reward contingency learning, both arousal-induction methods led to impaired performance. These results are discussed in terms of inconsistencies with Somatic Marker Hypothesis (SMH) predictions regarding task-relevant arousal, and background somatic state, and have important implications for future use of the IGT. On the Explicit Gambling Task (EGT), a novel probabilistic gambling task without involvement of reward contingency learning, increased arousal led to higher risk-taking where the choice of probabilities was most extreme. The EGT results have important implications for gambling tasks generally and are consistent with the interpretation of the detrimental arousal effects on the IGT as partly attributable to increased risk-taking. Effects of MTI arousal were also found on a Sexual Decision Making Questionnaire, and this is believed to be the first study to report an effect of nonspecific arousal on sexual behaviour intentions. The findings in this thesis are discussed in terms of the SMH, micro-economic theory, misattribution of arousal and the commonly used distinction between affective and deliberative models of information processing and decision-making. It is thus concluded that arousal (which may be non-specific, non-valenced, task-relevant or incidental) is an important factor in the relative shift in balance between 'cold' deliberative cognitive (S2) processes, which may better take account of long-term considerations, and 'hot' emotional (S1) processes more concerned with immediate reward (or avoidance of punishment). Increased arousal may therefore increase the tendency to engage a pre-potent response (as opposed to a more deliberate one), leading to behaviour which is more stimulus-bound and impulsive.