THE INTERNAL REPRESENTATION OF SPECTRAL CONTRAST IN HEARING-IMPAIRED LISTENERS

Abnormal frequency resolution associated with sensorineural hearing im pairment produces a smearing of spectral detail in the internal repres entation of complex acoustic stimuli. As a result, listeners with hear ing loss may have difficulty locating spectral peaks (e.g., vowel form ants) within stimuli which cue their identity. This study examined the relationship between frequency separation of peaks in a complex spect rum and the degree of spectral contrast preserved in the internal repr esentations in normal and impaired auditory systems. Hearing-impaired and normal-hearing subjects discriminated a flat-spectrum bandpass sti mulus from a stimulus containing a sinusoidal ripple across its freque ncy range. The peak-to-valley amplitude (in dB) necessary for detectio n of the ripple was measured for ripple frequencies ranging from 1 to 9 cycles/oct. Auditory filter characteristics were also measured at 1 and 3 kHz in order to examine the internal representations of the stim uli after cochlear processing. There were clear differences between gr oups in both auditory filter characteristics and spectral contrast det ection. However, the amount of contrast in the internal representation s predicted from these measurements was nearly the same for all subjec ts, suggesting that the reduced frequency resolution of the hearing-im paired group was largely responsible for differences in required peak- to-valley amplitude in the input spectra. Further, for all subjects, t here was a trade-off between the absolute level of internal contrast n ecessary for ripple detection and the number of samples of this contra st available to the listener.