This thesis reports upon a series of seven experiments with three central and connected objectives. Firstly, to characterise the cognitive processes associated with multiple-object tracking in terms of the Working Memory model utilising a dual-task paradigm and a series of secondary tasks known to tap specific WM processes. Secondly, to look for and, if found, account for expertise effects in the multiple-object tracking task, again using the dual-task paradigm. Finally, to investigate whether use or vividness of imagery can divide novices from such experts, as determined by analysis of self-report questionnaires. Results first supported the preattentive indexing process associated with the multiple-object tracking task, as reported by Pylyshyn and Storm (1988), and also demonstrated the additional involvement of serial, attentional processes. Of these, it is suggested that visuospatial processes are crucially active during the target acquisition phase when the objects are stationary and designated targets are flashing on and off. It is suggested that these may be associated with the formulation of a response bias, a target/distractor trial discrimination strategy and a target tracking strategy. Evidence is offered that counters the notion that just one of these stratagems is responsible for all the variation in performance. It was also shown that whereas modality-specific resources were primarily active during target acquisition, it was central executive processes that were pre-eminent during target tracking. Further, the multiple-object tracking task was shown to be one for which particular individuals have an advantage (i.e. radar operators), either by inherent ability or through training. This advantage is primarily evidenced during the target acquisition phase when such experts remain able to vary their response strategy advantageously, even in the presence of a demanding secondary task. And it is mooted that such an advantage may arise either because of an inherent ability to resist such interference or because, through automation, these mental processes require fewer attentional resources. Finally, it was shown that males' and females' use of imagery is differentially correlated with a central measure of the multiple-object tracking task, namely the ability to discriminate target from distractor trials. Since experts primarily show the same, negative correlation as novice males it was hypothesised that radar operator training, at least in part, either actively involves a positive discouragement of the use of imagery or that few females complete radar operator training because they are not suited to the task as they make too much use of imagery. Further, that radar operator training either positively enhances vividness of imagery, since only experts showed a significant correlation between vividness of imagery and target/distractor discrimination, or that those who successfully complete radar operator training do so, at least in part, because of an inherently more vivid imagination.