Current theories of visual processing are theories of local responses. Even models of space-variant acuity concentrate on properties of the local receptive fields, with the rationalization that the visual system is approximately homogeneous within any small neighborhood. The response of the entire visual field is pieced together from models of local responses. The theory of integral operators allows the experimentla study of human acuity to be united with computational model is visual processing. Their use in this context leads to simpler and more intuitive proofs of key theorems which relate threshold assessment to eigenvalue problems. At the same time, everyday experimental concepts, such as threshold sensitivity, take on new elegance when placed within the theory of integral operators.
