The study examines possible underlying mechanisms that may be responsible for generally observed biased response patterns in two conditional reasoning tasks: the Wason selection task and the conditional inference evaluation task. It is proposed that memory processes that may account for priming phenomenon, may also account for the phenomena of matching bias and double-negation effects in reasoning. A new mental activation model is proposed, based on distributed theories of memory, which models relevance effects of the problem materials by way of a simple algorithm. The model is seen to parsimoniously predict previous general response patterns found using the two reasoning tasks and makes unusual predictions concerning the size of the concepts used in the reasoning problems. The findings show that matching bias can occur between materials that do not lexically match but correlate on a semantic basis, which clarifies a previously uncertain area in the literature. It is also shown that previously deemed 'irrelevant' or mismatching cards on the selection task can interfere with the perceived relevance of matching cards if they are semantically related. The findings also show a weak but significant effect of concept size on matching bias in the inference task, supporting the proposed mental activation model. Issues concerning the notion of relevance perceptions being measured by particular response choices are raised with respect to both the selection and inference tasks.

This thesis concerns the content of mental representations. It draws lessons for philosophical theories of content from some empirical findings about brains and behaviour drawn from experimental psychology (cognitive, developmental, comparative), cognitive neuroscience and cognitive science (computational modelling). Chapter 1 motivates a naturalist and realist approach to mental representation. Chapter 2 sets out and defends a theory of content for static feedforward connectionist networks, and explains how the theory can be extended to other supervised networks. The theory takes forward Churchland’s state space semantics by making a new and clearer proposal about the syntax of connectionist networks − one which nicely accounts for representational development. Chapter 3 argues that the same theoretical approach can be extended to unsupervised connectionist networks, and to some of the representational systems found in real brains. The approach can also show why connectionist systems sometimes show typicality effects, explaining them without relying upon prototype structure. That is discussed in chapter 4, which also argues that prototype structure, where it does exist, does not determine content. The thesis goes on to defend some unorthodox features of the foregoing theory: that a role is assigned to external samples in specifying syntax, that both inputs to and outputs from the system have a role in determining content, and that the content of a representation is partly determined by the circumstances in which it developed. Each, it is argued, may also be a fruitful way of thinking about mental content more generally. Reliance on developmental factors prompts a swampman-type objection. This is rebutted by reference to three possible reasons why content is attributed at all. Two of these motivations support the idea that content is partly determined by historical factors, and the third is consistent with it. The result: some empirical lessons for philosophical theories of mental content.

This study has focused on cognitive aspects of the human processes involved in relevance judgements. Several criteria and a great number of measures have been proposed and used for relevance assessment. However, there is a lack of agreement as to which are the best measures and to what extent they are affected by variability of relevance judgements. The purpose of this research was to identify those cognitive factors, which primarily contribute to relevance judgement. In tills study, sixteen criteria that influence cognitive relevance were identified and used. The study addressed three questions: (1) What cognitive factors affect relevance judgement? (2) What is the importance of each factor on relevance judgement? (3) Do the factors remain stable over time? Both qualitative and quantitative techniques were used for data collection and analysis. Structural Equation Modelling (SEM) as a multivariate technique was used to develop a statistical model of cognitive relevance. It seems, it is the first time that this technique has been applied to measure cognitive factors of relevance. Saracevic's (1996) stratified model, as a cognitive IR model was adopted to provide a necessary framework to incorporate relevance cognitive theory and a user approach in measuring relevancy.

The functions of the retrosplenial cortex are not clearly understood, and the two current theories of retrosplenial cortex function, the translation and integration theories, are frequently very difficult to distinguish from each other, particularly in the spatial domain. The principal goal of this thesis was to differentiate between the integration and translation theories, and to explore the functions of the retrosplenial cortex in tasks that minimise or remove spatial demands, particularly navigation. The work presented in this thesis demonstrates that the retrosplenial cortex is involved in tasks extending beyond the spatial domain into executive functions and cross--‐modal processing. The retrosplenial cortex has been shown to be required for visually determining location in an environment, in the absence of self--‐generated navigational cues. Further evidence has been presented for the differing roles of the retrosplenial sub--‐regions, which appear to work in conjunction with each other to combine information received from different sensory modalities. However, further work is required to fully understand the ways in which these areas work together and with other areas of the brain, and the implications that dysfunction in this area has for human cognition.

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