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

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
(f_c) equal to: 250, 500, 1000, 2000Hz, and for modulation frequencies
(f_m) equal to: 4, 8, 64, 128, 256Hz. It was stated that for low
f_m the determined detection thresholds for the normal-hearing subjects
were roughly similar to those for the cochlear-impaired subjects. However, for higher
f_m 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
f_m, 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
f_m greater than the critical band, the loudness of AM signals increased
with f_m for the normal-hearing su bjects, whereas it remained independent
of f_m for the hearing-impaired subjects.