Much of what we know about the physical world is afforded to us by vision. With age, our ability to perceive visual information can become compromised, affecting our autonomy and quality of life. Given the rapid aging of populations worldwide, it is imperative to develop a comprehensive understanding of the effects of age on visual function. Therefore, the aim of this thesis was to use psychophysical methods to examine the effects of 'healthy' aging on visual perception, with a particular emphasis on furthering our knowledge of age-related reductions in the perception of motion. In a series of experiments, observers ranging from 18-82 years of age were tested and compared on psychophysical tasks which measured orientation and direction sensitivity, first- and second-order global motion perception, contrast sensitivity, and visual attention as measured by the Useful Field of View. Four key findings are presented within this thesis: (1) older observers demonstrate reductions in orientation and direction sensitivity that can be attributed to increased internal noise in the aged motion pathway, (2) age related impairments in global motion perception are mediated by reductions in spatial integration, (3) older female populations may be particularly susceptible to age-related impairments in motion perception, and (4) there may be a selective impairment in the processing of second-order radial motion in the aged. The results of these experiments indicate that whilst some aspects of motion processing remain preserved with age, older observers demonstrate marked impairments on a number of motion tasks.

In order to perform at the highest level, athletes will acquire information from all of their sensory systems. It would be intuitive to assume that the most vital information for the majority of sports-related tasks will be gathered via the visual system and that this visual input. tends to override information from other sensory sources. Research is beginning to highlight the links between the ability to quickly and accurately pick up visual information and quality of performance in a range of sports (Erickson, 2007). The purpose of this thesis is to investigate the visual skills of elite athletes and the effect of these visual skills on performance at the highest level of sport. The first experimental chapter aims to assess the current level of visual skills present in athletes of the highest level and compare these to lower level athletes, as well as by gender and sport. The thesis then goes on to develop a tool to use in order to assess the visual demands of a particular sport. In Chapters Four and Five visual training programmes are used with the aim of improving visual skills of elite athletes. In one study improvements are measured by playing position and the next applies different methods of vision training and improvements are measured not only in visual skill but also in sport-specific skill. Finally Chapter Six uses fMRI to compare the different brain function of expert athlete with novices. This thesis has shown that athletes from different sports, genders and abilities show assorted visual skills. It has also developed a tool to uncover which visual skills an expert considers most important for their sport. The training studies have proved successful in improving not only the visual skills of elite athletes but also their sport specific skills. Finally, it has been shown that experts use different areas of their brain when making sporting judgements, regardless of whether the decision is in the sport in which they excel or in an unfamiliar sport.

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Attended images prime both themselves and their left-right reflections, whereas ignored images prime themselves but not their reflections (Stankiewicz, Hummel, & Cooper, 1998). These and other effects are predicted by the hybrid theory of object recognition (Hummel & Stankiewicz, 1996a) that the human visual system represents ignored images holistically (i.e., view-based), and attended images both holistically and analytically (i.e., part-based). In nine experiments using a naming task the predictions of the model were tested with split, plane-rotated and depth-rotated views of common objects. Consistent with the prediction of the hybrid theory, Experiments 1 and 3 demonstrated that split images primed their intact and split counterparts when they were attended but not when they were ignored, whereas intact images primed themselves whether they were attended or not. Experiment 2 demonstrated that a substantial component of the observed priming for attended split images was specifically visual. In Experiment 5, attended images primed themselves fnd their plane-rotated versions (90°) whereas ignored images only primed themselves but not their rotated versions. Experiment 6 tested whether rotated objects with a definite upright orientation prime themselves in the same view. Substantial priming was observed for attended and ignored objects when shown in their upright view. However, rotated objects with a definite upright orientation primed themselves only when attended but not when ignored. This result indicates that ignored images make contact with stored representations. Experiment 7 replicated the findings of Stankiewicz et al. for mirror images but with greylevel rendered 3D images. Experiment 8 tested priming for these objects using orientations in which parts change from study to test view. As before, there was substantial priming in all but the ignored-rotated condition. However, there was a greater reduction in priming for attended rotated objects than for ignored rotated objects. This result indicates that the representations mediating recognition of attended images are specifically sensitive to part changes. In Experiment 9, objects were rotated in depth such that equivalent parts were visible in both views. As in Experiment 7, the priming effects of view and attention were additive. These data provide strong evidence that one function of visual attention is to permit the generation of analytic (i.e., part-based) representations of object shape. At the same time these results show that object recognition is also mediated by additional holistic representations

This thesis is inspired by the growing domain of information visualisation, and the potentially open-ended choice of visual representations which can be used to represent any given abstract concept. Such a potentially unlimited choice means that the question of choosing an appropriate visual form is not insubstantial. This thesis therefore attempts to explore how to usefully inform such a choice through the concept of visual analogy. To this end a series of multidimensional icons are developed which differ in terms of level of analogy for a given concept. The practical studies outlined then set out first to confirm this difference in practical terms and then explore the implications of using different levels of explicit visual analogy in tasks appropriate to the use of multidimensional icons. The results reveal that a continuum of 'degree' of analogy can be practically established which increasingly constrains the interpretation users assign to representations as the level of analogy increases.

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This thesis is concerned with control over visual word recognition in the Stroop task. Besner et al. (1997) have argued that processing of the irrelevant (printed) word in the Stroop task can be endogenously controlled and claim that this is achieved by imposing a `mental set' during task performance that overrides a default mental set for reading by operating directly over visual word recognition processes. Their claim is based on a modified Stroop paradigm in which, when only one letter is coloured, the Stroop effect is reduced, and in some cases, eliminated. This is referred to as the Coloured Single Letter Effect (CSLE). An alternative view proposed by Mari-Beffa and colleagues, is that word reading in the single letter Stroop task can be automatic (Mari-Beffa, Estevez & Danziger, 2000). A series of experiments is reported using the Coloured Single Letter Stroop Task (CSLST). Experiments 1 to 3 address some criticisms levelled against the work of Besner et al. (1997) and the results show that overall their conclusions are secure. However in Experiment 4, a letter position is identified at which, when acting as the colour carrier, there is no reduction in the Stroop effect. This finding challenges Besner et al. 's view about endogenous control in the CSLST since it is not expected on their account of the CSLE. In Experiments 5-7 the position effect is explored further and found to be located near to the Optimal Viewing Position, a location formally defined as the position at which word recognition time is minimised. This position effect is then investigated by recording eye movements in Experiment 8. It is argued that the notion of an endogenous decisionmaker that influences visual word recognition in the Stroop task is not supported by the present set of results, but instead that exogenous factors are responsible