Comparing the level of the acoustic distortion product 2f1-f2with behavioural threshold audiograms from normal-hearing and hearing-impaired ears

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Abstract
The level of the acoustic distortion product, 2f1-f2, was measured across frequency from two different groups of adults: (1) a group of 57 drawn from the university population who considered that they had normal hearing and (2) a group of 26 patients referred from the ENT Department of the County Hospital. These patients complained of reduced 'quality' of hearing, but no organic condition had been diagnosed to explain it. Behavioural audiograms were obtained for both groups. In both groups of listeners the distortion frequency sweep is related to the respective subjective threshold audiogram. In subjects from whom distortion can be recorded across a wide frequency range, acoustic distortion product level and auditory sensitivity were significantly correlated in one-third of the subjects. In hearing-impaired patients acoustic distortion is usually detectable across frequency regions of normal hearing, but falls below the noise floor if hearing threshold levels are above 15-20 dB.