German physiologist and psychologist whose chief work concerned the physiology of colour perception. He taught at the University of Leipzig (1895), following professorships at the Josephs-Akademie, Vienna (1865–70), and at the University of Prague (1870–95). Hering challenged the colour-vision theory of Hermann von Helmholtz, postulating three types of receptors, each capable of a dual response to pairs of colours (yellow–blue, red–green, or black–white). He also investigated respiration and, with Josef Breuer in 1868, demonstrated the role of the vagus nerve in the regulation of breathing. This neural pathway was later referred to as the Hering-Breuer reflex.