Imaginal processing in the two hemispheres : a computational investigation.

Traditionally theories of cerebral organization have tended to focus on various broad functional dichotomies. However, whilst the identification of dichotomous dimensions distinguishing the hemispheres provides useful approximations of their functional properties, such dichotomies fail to account for the many diverse manifestations of hemispheric asymmetry. Recent research in cognitive psychology, however, indicates that mental faculties previously treated as undifferentiated phenomenon. are better described and understood as being composed of distinct processing units that perform specific operations. This evidence has led to the development of new computational models of functional cerebral lateralization. The phenomenon of visual mental imagery has achieved particular prominence in this respect as evidence has been produced in support of the claim that the generation component of the imagery system is lateralized to the left hemisphere (LH). Given these findings the question naturally arises as to whether other components of the imagery system are lateralized to the LH or whether both hemispheres are involved in different aspects of imagery performance. The thesis initially presents a review of the literature pertaining to the above, including methodological and theoretical issues related to the localization of function in the brain, models of hemispheric interaction, computational models of imagery developed within cognitive psychology, the relationship between imagery and perception and the evidence in support of the LH image generation hypothesis. A series of experiments isý then reported which wLýýs designed to investigate the possible lateralization of additional imaginal components. The first rive experiments investigated the putative LH localization of the image scanning component of the imagery system. A further three experiments are then presented designed to investigate the possibility that the two hemispheres are specialized for the generation of different forms of visual images. The implications of these findings for specific models of cerebral lateralization of the imagery system are then discussed, as are the implications for a general theory of cerebral organization.