Seeing and imagining in the cerebral hemispheres: A computational approach.

Visual recognition, navigation, tracking, and imagery are posited to share certain high-level processing subsystems. In the first part of this article, a theory of some of these subsystems is formulated. This theory is developed in light of an analysis of problems that must be solved by the visual system and the constraints on the solutions to these problems; computational, neurological, and behavioral constraints are considered. In the second part, inferences about perceptual subsystems are used to develop a theory of how mental images are generated. Support for this theory is adduced from studies of split-brain patients and a review of relevant neuropsychological findings. In the third part, a computational mechanism is developed to account for how visual function becomes lateralized in the brain; this mechanism is used to predict how the hypothesized processing subsystems become lateralized. In the fourth part, some critical tests of the theory of lateralization of perceptual processing subsystems are reported, and in the fifth part the theory is extended to account for the lateralization of image-transformation subsystems. In the sixth part, the theory is used to account for the almost ubiquitous variability (both between subjects and within subjects) evident in the neuropsychological literature on lateralization. Finally, in the concluding part of the article, the computational-neuropsychological approach is discussed and evaluated.