ACOUSTIC AND NONACOUSTIC FACTORS MODIFYING MIDDLE-EAR MUSCLE ACTIVITY IN WAKING CATS

MOST STUDIES OF THE MIDDLE-EAR MUSCLES have emphasized their reflex role in protecting the inner ear from damaging loud sounds (8,12, 13, 24, 26, 30, 36). Recent demonstrations of middle-ear muscle activity during lowintensity sounds (29) suggest that these muscles may have a wider role than merely protecting against mechanical damage. The present experiments reveal that in waking cats middle-ear muscle activity may be modified by prior acoustic experience, by nonacoustic factors such as bodily movements, and by changing the significance of the sound for the animal. This paper presents an analysis of some of the mechanisms underlying middle-ear muscle activity and illustrates both sustained and transient contractions which are regulated according to complex central activities, rather than responding as a fixed protective reflex arc