Archives of Acoustics, 20, 3, pp. 215-235, 1995

Detection and loudness of AM signals for normal and hearing-impaired subjects

W. Geers
D-44137 Dortmund, Westenhellweg 68

E. Ozimek
Institute of Acoustics, Adam Mickiewicz University, 60-769 Poznań, Matejki 48/49

The study comprises two experiments pertaining to the perception of sounds with
parameters changing in time, by normal-hearing subjects and by hearing-impaired subjects,
who had a sloping high-frequency hearing loss originating from a cochlear impairment. The
first experiment deals with the determination of the AM detection thresholds, for 3
normal-hearing and 3 cochlear-impaired subjects. In the second experiment, the loudness of
AM signals of different parameters, relative to the loudness of a sinusoidal tone was
determined by the same group of subjects. Measurements were made for carrier frequencies
(fc) equal to: 250, 500, 1000, 2000Hz, and for modulation frequencies
(fm) equal to: 4, 8, 64, 128, 256Hz. It was stated that for low
fm the determined detection thresholds for the normal-hearing subjects
were roughly similar to those for the cochlear-impaired subjects. However, for higher
fm the thresholds decrease for the normal-hearing subjects, whereas they
tend to increase for the hearing-impaired subjects. Thus, one can assume that for higher
fm, temporal resolution of the auditory system is significantly affected
by cochlear hearing loss. As regards the loudness of AM signals, the data showed that for
fm greater than the critical band, the loudness of AM signals increased
with fm for the normal-hearing su bjects, whereas it remained independent
of fm for the hearing-impaired subjects.
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