No change detected on distortion products in awake or anesthetized guinea pigs

Two pure tones presented simultaneously to one ear can produce physiologically and perceptively other tones called distortion products which originate in the inner ear. Notable differences exist between their physiological and perceptive features. In physiological experiments the anesthesia may alter the functioning of the cochlea, especially its efferent system. Physiological measurements made of distortion products taken from the same animals under anesthesia or in the awake state were compared using round window cochlear microphonic responses and evoked potentials from the eighth nerve and the auditory cortex. The physiological measures appeared unaltered by anesthesia, but in both the awake and anesthetized states, repeated measuring at intervals of several minutes could show apparently random variations of a few decibels.