Two explanations exist in the literature for consumption-related pleasantness reduction: sensory-specific satiety and alliesthesia. Sensory-specific satiety describes the phenomenon that the sensory characteristics of an eaten food decline in pleasantness, whilst alliesthesia predicts that pleasantness depends on internal need. Experiment 1 investigated the contribution of both phenomena to consumption-related pleasantness reduction in a snack context. This was important since the presence of negative alliesthesia was questionable and recovery from sensory-specific satiety remained to be explored. There was no evidence for alliesthesia and although the results suggested the presence of a low threshold for a rapid, uniform and small effect of energy on pleasantness, no such threshold was evident in Experiment 2. Subsequent experiments explored sensory-specific satiety in greater depth. Experiment 4 investigated the effect of current energy needs on sensory-specific satiety and Experiment 5 the effect of food presence in the gastro-intestinal tract. Experiment 3 was a methodological study designed to determine the most appropriate portion size for these experiments. Both these post-ingestive variables had no effect, and in Experiments 1, 2 and 4, sensoryspecific satiety was unaffected by nutrient intake. Experiment 6 investigated an effect of flavour intensity but pleasantness reduction was minimal in each condition. This may partly have been due to the absence of an uneaten sensory contrast, as such a contrast enhanced sensory-specific satiety in Experiment 7. Experiment 8 reinvestigated the effect of flavour intensity and the effect of an uneaten sensory contrast. In this instance, an uneaten sensory contrast had no effect, possibly because the methodology interfered with pleasantness reduction. There was a trend for an effect of flavour intensity but this was complicated by differential initial liking. In conclusion, the results suggest that sensory-specific satiety contributes to consumption-related pleasantness reduction in a snack context but not alliesthesia. Sensory-specific satiety may generally be more transient in a snack context, and sensory and cognitive variables may influence this phenomenon but not post-ingestive feedback.

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This thesis tests a new theory of craving: The Elaborated-Intrusion Theory of Desire. The theory incorporates aspects of current conditioning, neurophysiological and cognitive theories and expands on existing knowledge of craving. The theory suggests that human desire involves intrusive thoughts and elaborated cognitions and also introduces mental imagery as a key aspect of the craving episode. There are two broad areas of research conducted in this thesis. The first explored the subjective experience of craving using two questionnaire studies. The results from these questionnaire studies acknowledged the generality of craving, indicating that the subjective experience of desire was similar across different target substances and it confirmed that visual imagery was a component of craving. The second area of research focuses on this relationship between visual imagery and craving. Experiments 1 to 3 tested visual imagery and working memory manipulations in deprived and continuing smokers. They provide empirical support for the hypothesis that craving can be reduced by a concurrent task that selectively loads the cognitive processes involved in generating and maintaining an image of the craved substance. The final experiment was an intervention study testing the potential for using visual imagery methods to manage cravings outside the laboratory. However, the visual imagery task did reduce smoking behaviour over a one-week 'treatment' period in a group of smokers wanting to quit, an auditory imagery task had a similar effect. The results overall support the contention of the EI theory that visual imagery is a key component in desire. Despite the equivocal results of Experiment 4, the findings highlight the potential for imagery interventions to help manage craving in therapeutic setting.

Fatigue is a familiar and commonplace occurrence, but attempts to investigate the nature of fatigue have been inconclusive. Following more than a hundred years of extensive research, the construct is still ill-defined. This has resulted in a series of different strands of research, producing results concomitant with each researcher's own idea of what constitutes fatigue. Two central questions remain unresolved: (1) what sort of a construct is fatigue? and (2) should fatigue be conceptualised as a single, one dimensional state, generated by a range of different conditions, or a multidimensional state, incorporating a number of distinct but related states? There is an implicit assumption within the literature (and every-day language) that there is more than one 'type' of fatigue. However, there is currently no theoretical model which outlines the types of fatigue which should be incorporated in a theoretical framework and which explains the relationships between these fatigue types. The work presented in this thesis represents an attempt to address these issues using both psychometric and experimental approaches. Preliminary work investigated the psychometric basis for a unitary or multidimensional construct. This separately addressed the constructs of state and trait fatigue and, on the basis of the findings, state and trait multiple fatigue questionnaires were developed. A series of four experiments were then carried out which manipulated different types of work to facilitate an investigation of the dynamic development of fatigue. The first three experiments focused on the separate effects of mental and physical fatigue, and the final experiment considered the nature of their interaction.Both experimental and psychometric analyses supported the proposition of a multidimensional construct. The evidence in support of a multidimensional construct of trait fatigue was particularly strong. However, while the evidence in support of a multidimensional construct of state fatigue was less convincing, the experimental manipulations of different types of workload did produce states of fatigue that were subjectively different and also different patterns of fatigue after-effects.