The Intra-Aural Muscle Reflexes in Normal Persons and in Workers Exposed to Intense Industrial Noise

Abstract

Series of normal persons, and workers exposed continuously to traumatic noise levels were examined with respect to the threshold and the period of latency of the intra-aural muscle reflexes, as measured by the impedance method. The results were identical. The sensitivity of the reflex pattern towards artificial pressures to the ear drum was investigated in all persons. In about one-third of the whole material such a sensitivity was present and two separate types could be established, which were found to be closely correlated to the type of movement of the ear drum, which is induced during such reflexes. This phenomenon is considered as objective evidence of the existence of acoustic reflexes in both intra-aural muscles and it is concluded, that the period of latency which under ordinary circumstances is found by the impedance method is the one of the tensor muscle. The investigation seems to confirm the functional identity as to these muscles in experimental animals and in human beings.