On the relation between frequency discrimination ability and the degree of hearing loss

The frequency discrimination ability was measured in a group of subjects with a sensorineuralhearing impairment and varying degrees of hearing loss. The measurements were made at the subject's most comfortable level. The results show very large variations in discrimination ability for the same degree of hearing loss. Based on the results, median and quartile values were calculated relative to the degree of loss in 10 dB intervals. Comparisons with the results obtained in other studies show, as a general tendency, a good agreement but, in some studies, differences in the value of the frequency DL occurred. This is most likely explained by the difference in the signal type and psychophysical technique used. Examples are given from measurements of subjects with other etiologies. The pure-tone audiogram gives limited information of the effect of a hearing impairment. It has, for example, in several studies been shown that speech-perception ability of a hearing impaired subject , especially in noise, cannot accurately be predicted from the pure-tone audiogram (Plomp & Mimpen, 1979; Pavlovic, 1984). It has also been shown that for subjects with a severe hearing loss, it is difficult to predict the performance on speech perception tests, even in quiet environments (Cramer & Erber, 1974; Plant, 1984). A possible explanation of these results is that the hearing impairment does not only result in a decreased sensitivity to sound but also, to a varying degree, in a reduced ability to perceive changes in frequency, amplitude, and time, and also in increased masking in the frequency and time domain. These different abilities can be called the signal-analyzing capacity of the ear. Up to the recent years, the signal-analyzing capacity of hearing-impaired subjects has been studied in a small nwnber of experiments only. In the 1950°s, some studies were made on the frequncy-discrimination ability of hearing-impaired subjects (Butler & Albrite, 1956; I-Iarris & Myers, 1955; Kijnig, 1957b; Meurman, 1954) and in the 1970's some studies were made on severely hearing-impaired children (Danaher, Osberger, & Pickett, 1973; Gengel, 1973; Martin & Pickett, 1970; Mdrtony, 1974; Pickett & Mktony, 1970; Risberg, ~elfors, & Boberg, 1975). Wing the last years, however, there has been an increased interest in this area and many articles have been published, e.g., Bonding (1979) , Festen & Plomp (1983), Fitzgibbons & Wightman (1982), Hoekstra (1979), Patterson, Mimmo-Smith, Weber, & Milroy (1982), Tyler, Wood, & Fernardes (1983), Zurek & Formby (1981). The aim of these studies have often been to try to explain hearing-impaired persons' difficulties in urderstanding speech in noise. STL-QPSR 4/1984 62 Congenital or Ute acquired early acquired Nmber of subjects 67 66