Abstract
The nature of sensory organisation - how information is transferred or recognised as equivalent between the various senses and whether a dominance hierarchy exists between them - is a topic which has interested man since at least the time of the ancient Greeks. This thesis focuses on the relationship between the visual and haptic senses and how this relationship changes during development. While it was previously known that adults achieve a unified percept in the face of conflicting visual and haptic information by a process of visual capture, there have been conflicting reports in the research literature on why this situation obtains and on the reactions of young children to such a situation. Two methodologies, the cross-modal transfer paradigm and the conflict paradigm, have been widely used in the study of sensory organisation. The conflict paradigm, used to explore possible sensory dominance hierarchies, has been widely criticised. In the present study a methodology has been developed which meets these criticisms; it has been used to study the hierarchical organisation of vision and touch in subjects from early childhood to adulthood. visual bias has been shown to occur across all age groups in haptic judgements of size, shape and texture regardless of the nature of the visual distortion. In contrast to most previous researchers, visual bias has been demonstrated to decrease with age and to be inversely related to haptic accuracy. The observed decrease in visual bias with age is accounted for in terms of the concomitant increase in the ability of subjects both to recognise the unnatural nature of the tasks they are being asked to perform and to adopt a problem-solving approach to the tasks. Through this type of approach all possible sources of information are sought and critically evaluated. A theory has been proposed to account for the occurrence of visual bias. The theory proposes that haptic judgements involve the transduction of the haptic information to a visual representation and that it is on this representation that all comparisons and judgements are made. According to this theory the occurrence of visual bias arises from the difficulty of developing an accurate transduction in the presence of similar but different visual information. The theory predicts that performance on a haptic task would deteriorate more in the presence of a simultaneous visual task than an auditory task of equivalent difficulty. This prediction has been tested and confirmed. The proposed theory has been shown to account for the order of difficulty normally reported for inter and intra-modal visual-haptic tasks and also to have explanatory value for data reported from other research into intermodal organisation.