In the Eye's Mind: Vision and the Helmholtz-Hering ControversyOne of the most persistent controversies of modern science has dealt with human visual perception. It erupted in Germany during the 1860s as a dispute between physiologists Hermann von Helmholtz, Ewald Hering, and their schools. Well into the twentieth century these groups warred over the origins of our capacity to perceive space, over the retinal mechanisms that mediate color sensations, and over the role of mind, experience, and inference in vision.