Partial dissociation of spontaneous otoacoustic emissions and distortion products during aspirin use in humans.

Otoacoustic emissions (OAEs) of two types--spontaneous and evoked distortion products--were studied before, during, and following a period of aspirin use. As previously reported, aspirin consumption uniformly reduced the spontaneous OAEs (SOAEs) to unmeasurable or extremely low levels. Aspirin consumption also reduced the amplitude of the evoked distortion products (EDPs) but did not eliminate them entirely. The amplitude of the EDP and its change with aspirin consumption were related to both the proximity of the EDP to the frequency of the SOAE and to the level of the primaries producing the EDP. At low primary levels, even with the SOAE absent (due to aspirin consumption, or suppression), EDPs near the SOAE frequency were 10-20 dB higher than when they were 100 Hz away from the SOAE frequency.

A method for relating loudness-matching and intensity-discrimination data.

A method that allows direct comparisons between pure-tone loudness-matching and intensity-discrimination data in normal and hearing-impaired listeners is described. This method makes a minimal number of assumptions about the relations between loudness perception and intensity-discrimination performance. Loudness is considered to be related to overall, perceived stimulus magnitude and intensity-discrimination performance is considered to reflect the accuracy with which a loudness judgment can be made. Because pure-tone intensity-discrimination performance varies as a function of stimulus level in normal ears, the standard level required to produce a particular difference limen in an impaired ear can be inferred from normal-ear intensity-discrimination data. Thus, plotting standard levels yielding normal difference limens as a function of standard levels yielding the equivalent sized difference limens from a threshold-shifted ear produces a function directly comparable to loudness recruitment functions. If loudness-growth and intensity-difference limens were tightly coupled in threshold-shifted ears, then stimuli that yield equal size difference limens would be equally loud. This relation was tested by obtaining loudness-matching and intensity-discrimination data from normal-hearing listeners with thresholds shifted by a wideband noise and hearing-impaired listeners with cochlear-type hearing losses. The results from these listeners show similarities between the traditional loudness-recruitment functions and "intensity-recruitment" functions derived from the assumed relation between the two measures. The primary difference between the functions is at low and moderate sensation levels where loudness grows at a more rapid rate than the difference limen.

The relations among critical ratios, critical bands, and intensity difference limens in man.

Band-narrowing estimates of the critical bandwidth (CB) are consistently larger than critical-ratio (CR) estimates for the same signal frequency. Bilger [in Hearing and Davis: Essays Honoring Hallowell Davis, edited by S.K. Hirsh et al. (Washington U.P., St. Louis, 1976), p. 191] proposed that this difference could be accounted for by reference to intensity-discrimination performance [CR(Hz)/CB(Hz) = delta I/I]. To test this hypothesis, band-narrowing, critical-ratio, and intensity-discrimination data were collected for four normally hearing, well-trained listeners. Signal frequency was 2000 Hz and two noise levels were used: 20 and 50 dB N0. The relations proposed by Bilger among critical-bandwidth estimates from band-narrowing experiments, critical-ratio estimates from pure-tone detection in wideband noise, and intensity discrimination for a critical-band-wide noise in wideband noise are not supported by the results of individual listeners, or results averaged across listeners.