Frequency modulation detection by normally hearing and profoundly hearing-impaired listeners.

The ability of normally hearing and profoundly hearing-impaired subjects to detect frequency modulations was evaluated under conditions where the amplitudes of the test signals were either constant (CA), sinusoidally modulated (SAM), or randomly modulated (RAM). Results for hearing-impaired listeners showed larger frequency difference limens (DLFM) than those for normally hearing listeners for all test frequencies (100 to 1000 Hz) and for all amplitude conditions. For both normal-hearing and hearing-impaired subjects, the DFLM was smallest for the constant amplitude condition and largest for the randomly modulated condition. Differences in performance between the RAM and CA conditions were generally much larger for impaired listeners than for normally hearing listeners. With random amplitude modulation, DLFMs for the hearing-impaired subjects were approximately 36 times larger than those for normally hearing subjects.