Spread of Masking in Ears Showing Abnormal Adaptation and Conductive Deafness

Abstract

Threshold measurements were made by Békésy sweep-frequency audiometry for pulsed tones in the presence of wide and narrow band noise introduced in the same receiver. Thresholds in the presence of various intensities of noise re 0.0002 dynes/cm² were compared for normal and pathologic ears. For all sensori-neural loss without abnormal adaptation, wide band noise produced a masked threshold 15–20 db below the level of the noise. The masked threshold at the center of the narrow band was approximately at the same intensity as noise. These findings are essentially the same as in normal ears. Conductively deafened ears showed the same masked thresholds as normal ears for white noise and for the center of the narrow band and for frequencies below. However, there was less spread of masking than normal for frequencies above the center of the narrow band. Cases with progressively increasing sensorineural hearing loss for frequencies above the narrow band showed most increased spread above the narrow band. Those with flat losses or more sensori-neural loss for frequencies below the narrow band showed a near symmetrical spread on each side of the narrow band. The clinical and audiological findings in the latter group indicated that the lesion was in the cochlea. For abnormally adapting ears white noise caused greater masking than for normal ears and masking effects at the center of a narrow band were also greater than in normal ears. In severely adapting cars, the lateral spread of masking approached the effect of white noise with narrow band masking.