1. the dwindling or shrinking of the tympanic cavity muscles, evoked by profound sounds, vocal expression, or moving of the body. This innate reaction decreases the low-frequency input that does into the inner ear canal and works in part to maintain said portion of the ear, keeping it safe from injuries that can result due to heightened sounds. 2. an inborn reflex to noise.

ACOUSTIC REFLEX: "The acoustic reflex safeguards the inner ear canal from being damaged when high-volume noises enter it."