Despite a 30-dB sound field, ANR audiometry can produce an audiogram identical to that obtained in a double-walled sound booth. ANR headphone audiometry improves the sensitivity of audiometric screening for mild low-frequency hearing loss. This technology may have important applications for screening in schools, industry, and community practices.

Intensity resolution and loudness matching behavior for pure tones was studied in quiet and in two levels of noise (15 and 40 dB spectrum level) to test the predictions of several models for relating these phenomena. Five normally hearing listeners participated. The Weber functions in noise were elevated compared to the ones in quiet when comparisons were made at equal sound-pressure levels (SPLs). Loudness matching functions (dB SPL in quiet versus dB SPL in noise) showed a slope greater than unity. Modified power functions with threshold corrections were fitted to the matching data to estimate the loudness function exponent. The best-fitting loudness exponent for individual and group data (range = 0.24-0.35) was in the range of values typically found using magnitude estimation procedures for the loudness equation yielding the best fit. Three models for predicting Weber functions from loudness were evaluated with this loudness representation. One of these models, the subjective analog to Weber's law, yielded results inconsistent with the observed data. The other models, McGill and Goldberg's [J. Acoust. Soc. Am. 44, 576-581 (1968)] neural counting model and the proportional-jnd theory, predicted Weber functions that are consistent with the observed data if the variance of the decision variable is assumed to change in quiet and noise backgrounds. The proportional-jnd theory has such a change built into the model, but the underlying physiological mechanisms responsible for its success are unknown.

Three experiments were completed to examine the effect of masker duration and spectrum on forward-masked intensity discrimination. Four listeners participated in each experiment. Intensity discrimination was measured in quiet and in the presence of forward maskers using adaptive forced-choice procedures. The standard duration was either short (10 ms) or long (250 ms) in experiment 1 and short (10 ms) in experiment 2. The standard always occurred 100 ms after the offset of the masker. In the first experiment employing 1.0-kHz maskers and standards, a short duration masker (10 ms) produced more masking than a long duration masker (250 ms). A mid-level elevation of the Weber fraction was observed for all conditions. To ensure that the results of experiment 1 were not influenced by off-frequency listening, the second experiment employed a broadband noise masker. As before, a short duration (10 ms) masker produced more masking than a long duration masker (100 ms) and a mid-level elevation of Weber fractions was observed. This outcome is inconsistent with a peripheral sensory effect for which an increase in masker duration should result in a greater amount of adaptation, and, as a consequence more masking. A third experiment employing a broadband noise masker and standard showed the greatest amount of masking for low-level standards, but only when the duration of the masker and standard was short. This result is similar to one seen for a single listener in the first experiment for short duration tonal maskers and standards. For this listener, a second tone presented at 4.133 kHz presented simultaneously with the 1.0 kHz masker reduced significantly the amount of masking for low-level standards, but the mid-level elevation of the Weber fraction remained. Taken together, these results suggest that perceptual similarity plays a role in forward-masked intensity discrimination but does not account entirely for the mid-level elevation of the Weber fraction.

Forward-masked intensity discrimination shows elevated just-noticeable differences (jnd’s), for mid-level standards, a finding argued to be consistent with sensory adaptation [F. Zeng and C. W. Turner, 782–787 (1992)]. Accordingly, the size of jnd’s should increase with increases in masker duration. We tested this notion by measuring forward-masked jnd’s as a function of level for 1000-Hz tones in four listeners with normal hearing. Jnd’s were measured for 10-ms standards in quiet and in the presence of a 1000-Hz masker with either a 10-ms or a 250-ms duration. The masker level was fixed at 90 dB SPL and the interval between masker offset and standard onset was 100 ms. Forced-choice procedures were employed. The results show significantly less masking for the longer duration masker (250 ms) than for the short one (10 ms). These results are contrary to the results reported for forward-masked detection. Listening bands revealed by measuring jnd’s as a function of masker frequency suggest that off-frequency listening may be responsible for this finding [Work supported by the Bryng Bryngelson Fund.]