Abstract
Recognition of Morse signs masked by noise was measured in five hearing-impaired telegraph operators with a high-frequency hearing loss. They all described problems typical for subjects with high-frequency hearing loss, i.e. problems with recognition of speech in noisy environments. Telegraphy speed, listening level, bandwidth of the masking-noise, frequency and interaural phase were systematically varied. At narrow-band masking with a bandwith of 230 Hz (1/3 octave 891 1121 Hz) centred at 1000 Hz no statistical significant difference in recognition of telegraphy signs was found between the hearing-impaired subjects and the normal-hearing subjects investigated in our earlier studies at any telegraphy speed or at any S/N ratio. All hearing-impaired subjects improved in recognition when the telegraphy speed was lowered. When a broad-band noise (100–2500 Hz) was used as a masker all the hearing-impaired subjects improved in recognition when the frequency was lowered from 2000 to 500 Hz. At 40 signs/min telegraphy speed the hearing-impaired subjects showed a significantly lower recognition (p < 0.05) at low S/N ratios both at 2000 and 500 Hz frequency compared to the normal-hearing subjects investigated in our earlier studies. At monaural listening the normal-hearing subjects were significantly better (p < 0.01) in recognition. When the telegraphy signs were presented 180° out of phase between the two ears, all subjects improved in recognition compared to when the telegraphysigns were presented in phase. This improvement was equal in hearing-impaired subjects and in the normal-hearing subjects investigated in our earlier studies.