Johannes Müller (1801-1858) demonstrated that there are five types of sensory nerves; furthermore, each nerve type, when stimulated, results in its own characteristic sensation. (In the older view, sensory nerves were nonspecific and could transmit any sort of sensory information.) Thus, the same stimulus (e.g., a blow to the head) may produce different sensations (e.g., pain, a flash of light, noise) depending on what nerves of sense were activated (e.g., tactile, visual, auditory). The doctrine also states that the mode of stimulation does not alter the characteristic sensation. For example, light, pressure, or mechanical stimulation of the optic nerve invariably produces a visual sensation. However, the mode of stimulation is not irrelevant: sensory nerves are maximally responsive to certain forms. Müller referred to this phenomenon as "specific irritability," later to become known as adequate stimulation. Returning to the example above, while the optic nerve may be stimulated by pressure, it is most sensitive to light waves. As Boring (1950) points out, "A pressure is not actually an 'inadequate,' but a less than adequate, stimulus to vision" (p. 87).