  Modern psychologists regard Mach as the forerunner of the idea of neural nets in perception. He discovered that the eye has a mind of its own; we perceive not direct stimuli but relations of stimuli. The visual system operates through a process of continual adaptation of the present sensation to previous ones. We do not experience ‘reality’ but rather experience the after effects of our nervous system’s adaptations to new stimuli. Furthermore, from an evolutionary perspective, it was necessary that this relational nature of perception be so. What were once thought of as errors of the brain, Mach showed to be adaptations. His argument is brilliant and he is cited even today in psychology textbooks for these contributions. Furthermore, his work in physiology influenced his epistemology. If we perceive not things directly but contrasts of things, then the world is a biological construction formed through the process of our nervous system adapting to new sensations. Representationalist theories of perception, which posit a direct correspondence between appearance and reality, become untenable.