Discrimination of Rippled Spectra by Listeners with Impaired Hearing in Two Experimental Schemes

Studies in listeners aged 30–82 years measured the frequency resolution power(FRP) of hearing as the maximum density (cycle/oct) of spectrum ripples at which a signal with a ripple spectrum could be discriminated from a signal with a different arrangement of ripples on the frequency scale or from a signal with a “flat” spectrum (without a ripple pattern). Signals had either a two-octave spectral bandwidth centered at 1, 2, or 4 kHz or a wide spectral bandwidth (six octaves, 0.125–8 kHz). Listeners over 60 years of age showed a significant increase in tone detection thresholds as compared with the norm (hearing loss). FRP was found to correlate with tone detection thresholds: the higher the threshold, the lower the FRP when the listeners was required to discriminate between signals with ripples in different positions on the frequency scale. This relationship was statistically significant and ranged from −0.04 to −0.07 (cycle/oct)/dB for both 2-oct and 6-oct signals. It is suggested that discrimination of the two signals in this situation was due primarily to the spectral mechanism and depended on the ratio of the ripple density in the signal spectrum and the sharpness of the auditory filters. When the task was to discriminate between ripple and flat signals, the relationship between FRP and tone detection thresholds for 2-octave signals was not statistically significant. The relationship was statistically significant for wideband signals, amounting to −1.23 (cycles/oct)/dB. It is suggested that discrimination between signals with ripple and flat spectra is due primarily to temporal analysis and depends on the width of the range of perceptible frequencies.