Acoustic reflex testing is a procedure used to evaluate the function of the middle ear muscles, specifically the stapedius muscle, in response to loud sounds. It helps assess the health of the auditory pathway, including the inner ear, auditory nerve, and brainstem. The test involves measuring the contraction of the stapedius muscle in response to a loud sound, which is an involuntary response that stiffens the middle ear and reduces its ability to conduct sound.