A New Measure for Determining the Degree of Abnormality of Psychophysical Tuning Curves in Hearing-Impaired Subjects

Abstract

Psychophysical tuning curves were determined in hearing-impaired and normal-hearing subjects. Frequency selectivity, determined from the tuning curves of the hearing-impaired, decreased with increasing hearing impairment. As this may be attributed to the subjects' hearing impairment as well as to the inevitably higher test (probe)-tone level, we also collected psychophysical tuning curves from normal-hearing subjects as a function of test-tone level. Their frequency selectivity also decreased with test-tone level, but to a lesser degree. This indicates a real decrease in frequency selectivity in hearing-impaired subjects. Two measures were used to describe frequency selectivity, the d1oct and the newly introduced AALD. The latter is the average absolute difference in masker levels between the individual's psychophysical tuning curve and the average normal tuning curve, obtained at the same test-tone level. The AALD turned out to be a more sensitive tool for measuring pathological frequency selectivity than the d1oct.