THE VALUE OF EFFORT: HOW DO WE MAKE DECISIONS WHEN EFFORT IS INVOLVED?
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Effort-based decision-making is an instance of value-based decision-making in which effort is the main cost associated with obtaining rewards. Despite the fact that we engage in this process on a daily basis, many assumptions regarding effort-based decision-making have not been tested yet. Furthermore, no comprehensive model of this type of decision-making has been proposed. Therefore, the main aim of this thesis was to introduce a novel Value-Effort Decision-Making (V-E-D-M) model of effort-based decision-making. The proposed model consisted of six processing stages: Representation, Valuation, Action Selection, Action Execution, Outcome Evaluation and Learning. Assumptions of this model were investigated in this thesis to verify their validity. More specifically, six areas relating to the V-E-D-M model were explored: the effects of manipulating 1) reward characteristics and 2) effort type on effort-based decision-making, 3) importance of effort/reward during different stages of effort-based decision-making, 4) importance of outcome feedback during effort-based decision-making, 5) effects of delaying Action Execution on effort-based decision-making, and 6) neural underpinnings of the effort-based decision-making process. These topics were explored in six experimental studies utilising a novel effort-based decision-making task developed for the purpose of this thesis. The results of these investigations showed that: 1) the effects of reward magnitude on effort-based decision-making depend on the stage of the process, as rewards seem to affect behaviour mainly during Action Selection, and less so during Action Execution; 2) changing reward valence affects effort-based decision-making, as people become more risk averse when losses are at stake, 3) reward reliability can potentially affect effort-based decision-making, but only when participants believe they can increase their chances of obtaining rewards through exerting effort, 4) reward values drive behaviour during Action Selection, whereas effort requirements determine behaviour during Action Execution, 5) increasing the informative value of outcome feedback does not affect effort-based decision making, and 6) delaying Action Execution affects effort exertion during this stage. The final V-E-D-M model incorporates these results.
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