Toward a science of individual differences in vision: An investigation of motion perception and oculomotor pursuit

The study of individual differences in vision has much to offer both basic science and the science of group differences. For example, research on individual differences in color vision has taught us about basic functional mechanisms and their underlying genetics while also informing us about color blindness and its differing prevalence between males and females. Despite such utility, individual differences in vision are rarely studied. This dissertation seeks to demonstrate by example the value, to both basic science and the science of differences between groups, of studying individual differences in vision.;In paper one, we show evidence for two independent visual motion processing deficits in developmental dyslexia, each associated with a different reading deficit. A consideration of individual differences in this study allows us to establish that these deficits are independent, while providing evidence that our two motion processing measures may rely upon independently varying processes in normal populations as well. In paper two, we report independent associations between individual differences in two types of motion processing and two periods of oculomotor pursuit. There is a clear transition between these two associations at the time of the initial saccade, evidence that the motion signals driving presaccadic pursuit differ from those driving postsaccadic pursuit. This study both informs us about the nature of signals driving smooth pursuit and provides a useful point of departure for clinical investigations involving smooth pursuit. In paper three, we demonstrate a sex difference favoring males in precision of smooth pursuit eye movements, which could underlie male advantages seen in gross visuomotor performance. This sex difference is independent of the associations reported in paper two, and we show evidence that the difference is likely to be one of internal monitoring of eye movement commands, or efference copy. Given extensive knowledge of factors that differentially affect development of men and women, the further investigation of this sex difference could aid our understanding of the development of oculomotor function.;We propose that a healthy science of individual differences in vision could lead to insights applicable to both basic science and the science of group differences.