[Acoustic and mechanical interpretation of the "on-off" effect].

The on-off effect is a particular form of the stapedial reflex. It is presented as a double positive deflection appearing when the stimulus starts and stops. This type of reflex is very frequent in beginning otospongiosis. The mixed theory assimilates the annual ligament of the stirrup to an elastic pin which obeys the physical laws of a spring. Otospongiosis produces a shortened sement and thickening of the annular ligament, with an increase in its rigidity, responsible for deafness of the low sounds at the beginning of the disease. The acoustic and mechanical theory enables a clear explanation of the lines supplied by the different types of instruments (220 Hz or 600 Hz). It also specifies the role of the annular ligament in various hearing pathologies.