| Summary: | Beliefs and desires are two core mental states that enable us to understand human behaviour. Research in developmental psychology reveals that children understand desires earlier than beliefs, suggesting that the cognitive processes underlying desire reasoning are less complex or less effortful than the processes underlying belief reasoning. Recent findings from studies with adults have identified a specific neural network associated with belief reasoning and found that belief reasoning is cognitively effortful even for healthy adults. However, there has been very little research into the cognitive and neural processes involved in desire reasoning in adults and the extent to which these processes are distinct to those involved in belief reasoning. In Chapter 2, I directly compare the performance of adults with acquired brain damage in belief and desire reasoning tasks, and I suggest the existence of two separate processes in desire reasoning: one linked to self-perspective inhibition and one linked to the reasoning about avoidance desires. In Chapters 3 and 4 I further assess these processes in healthy adults and show that both lead to a measureable cost in the participants’ performance. This provides the first report that desire reasoning (and not only belief reasoning) is cognitively effortful for healthy adults. In Chapter 5, I document a double dissociation in adults with acquired brain damage showing that the processes mediating self-perspective inhibition and those mediating the reasoning about avoidance desires are executive in nature but functionally and neurally distinct. In Chapter 6, I discuss the implications of the findings for the understanding of how beliefs and desires are processed in the adult mind and brain.
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