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Autistic Spectrum Disorders (ASD) are characterized by difficulties in reciprocal social interaction and communication, with restricted interests and stereotyped behaviours (ICD-10 criteria World Health Organisation, 1996). Many of the difficulties experienced by individuals with ASD have been attributed to deficits in mentalising- the ability to attribute mental states to oneself and others in order to explain and predict behaviour. This thesis begins by considering the contribution that advanced theory of mind tasks have made to our understanding of mentalising abilities in ASD. It is concluded that there is substantial evidence that even the highest functioning individuals experience difficulties with mentalising. However, further progressing our understanding of mentalising in ASD will require a number of methodological improvements- in particular, greater attention given to controlling the effects of IQ and executive functioning. The empirical paper draws on these methodological points and explores mentalising and other aspects of social cognition in children excluded, or at risk of exclusion, from primary schools. Previous research has suggested that a sub-group of these children may have unidentified ASD (Gilmour, Hill, Place, & Skuse, 2004). The current study assessed primary school children on a range of measures of social cognition, including theory of mind. Children excluded from school were significantly more likely to meet ICD-10 criteria for ASD than comparisons. Furthermore, they were significantly more likely than comparisons to show deficits in social cognition and mentalising similar to those documented in ASD. It is concluded that there is strong evidence for a sub-group of children excluded from school with unidentified ASD. The critical appraisal expands on the implications of these findings, focusing on the issues involved in screening for ASD, and reflecting on clinical issues raised by the research.

Optical and electrical techniques are used to characterise deep- levels in silicon that could have applications in extrinsic silicon thermal imagers. The concentration of indium in indium-doped silicon substrates is estimated from Hall-effect and capacitance-voltage measurements together with chemical analysis and infra-red absorption. Junction space-charge measurements on diode structures are used to give information on the thermal emission rate, photoionisation cross-section, and enthalpy values of impurities and radiation-induced defects in silicon. The responsivity, noise and detectivity of indium-doped silicon detectors are measured and found to be in very good agreement with calculated values of these quantities. A model for the responsivity is developed which explains the general features of the experimental responsivity results in terms of capture and emission processes from acceptor levels. Finally, the use of the punch-through technique to produce a compact monolithic extrinsic silicon thermal imager is described and results of its low temperature operation are given.