ABSTRACT
Whatever the limitations of human visual psychophysics may be, human visual psychophysics has one important advantage compared with studies of animal visual pathways and with studies of computer vision: if one's aim is to understand human vision, there is no substitute for empirical studies of vision in humans. From Fechner onward the development of classic psychophysical methods has been motivated by the aim of rendering certain aspects of mental experience amenable to quantitative scientific methods. An important point about linear behavior is that the same method of linear systems analysis can be used with any linear system. The psychophysical effect of an auxiliary signal is closely similar to the linearization phenomenon that is well known in engineering. When an object moves along a trajectory that passes between the eyes, the two retinal images move in opposite directions, and when the trajectory passes wide of the head the two retinal images move in the same direction.
