Abstract
A novel approach to studying visual function, involving the psychophysical evaluation of individual differences, is proposed. By assessing covariation between individuals' performance on tasks assessing multiple visual functions, one may estimate the degree to which these functions are subserved by common underlying mechanisms. This approach is conceptually identical to approaches that associate multiple functions with similar brain regions or brain responses. As with those established methods, functions of interest are isolated with the help of carefully chosen control conditions, then mapped onto an independent source of data: in this case inter-individual variation in performance, in the established cases brain structure or brain function. This approach presents a converging method for addressing questions of functional association, one that adds to our theoretical leverage by relying upon different assumptions than those of physiology-based methods. A study of individual differences in motion processing is presented as a methodological and conceptual illustration of the utility of this approach.