Two mechanisms for motion perception in the human visual system

Previous studies have suggested that the human visual system involves a contrast motion mechanism as well as a luminance motion mechanism. The positive motion after-effect with a compound grating shows that these two mechanisms are distinct processes operating independently. The authors report a series of experiments which compare the spatio-temporal properties of two kinds of motion mechanisms. The results suggest that the contrast motion mechanism involves a motion extraction stage similar to the luminance motion mechanism, and a preprocessing stage which is more elaborated than a simple nonlinear transformation such as rectification