High Ripple-Density Resolution for Discriminating Between Rippled and Nonrippled Signals: Effect of Temporal Processing or Combination Products?

The goal of the study was to investigate the role of combination products in the higher ripple-density resolution estimates obtained by discrimination between a spectrally rippled and a nonrippled noise signal than that obtained by discrimination between two rippled signals. To attain this goal, a noise band was used to mask the frequency band of expected low-frequency combination products. A three-alternative forced-choice procedure with adaptive ripple-density variation was used. The mean background (unmasked) ripple-density resolution was 9.8 ripples/oct for rippled reference signals and 21.8 ripples/oct for nonrippled reference signals. Low-frequency maskers reduced the ripple-density resolution. For masker levels from −10 to 10 dB re. signal, the ripple-density resolution for nonrippled reference signals was approximately twice as high as that for rippled reference signals. At a masker level as high as 20 dB re. signal, the ripple-density resolution decreased in both discrimination tasks. This result leads to the conclusion that low-frequency combination products are not responsible for the task-dependent difference in ripple-density resolution estimates.

Effects of Decreased Audibility Produced by High-Pass Maskers in Younger and Older Adults

A recurring problem in aging research is separating the effects of age per se from the effects of high-frequency hearing loss. One approach is to present test stimuli in the presence of a high-pass masker to control confounding differences in high-frequency audibility across age groups. However, there is evidence that such maskers may affect older and younger listeners differently. In this study, pure-tone thresholds were measured for younger and older listeners in the presence of high-pass maskers. The age groups were carefully selected based on similar unmasked thresholds at each frequency. Thresholds were measured in quiet and in seven masker conditions. Both younger and older listeners showed increased threshold shift below the masker passband as the masker level increased. The degree of threshold shift was not greater for older versus younger listeners. Results suggest that high-pass maskers may be used to reduce high-frequency sensitivity differences between younger and older listeners without introducing differential masking effects.