The results of this study established a relationship between loudness and the ABR wave V latency for listeners with normal hearing, and flat cochlear hearing loss. In listeners with a sloping configuration of cochlear hearing loss, the relationship was not significant. This suggests that the click-evoked ABR may be used to estimate loudness growth at least for individuals with normal hearing and those with a flat configuration of cochlear hearing loss. Predictive equations were derived to estimate loudness growth for these groups. The use of frequency-specific stimuli may provide more precise information on the nature of the relationship between loudness growth and the ABR wave V latency, particularly for listeners with sloping configurations of cochlear hearing loss.

New analysis and measurement techniques have been developed to extend geophysical logging to the quantitative determination of the extent of fracturing, degree of alteration, and variation in lithostratigraphy of the oceanic crust. In Hole 504B in 5.9-Ma crust on the south flank of the Costa Rica Rift, a borehole televiewer was used to produce a fracture log of the upper crustal Layers 2A, 2B, and 2C. A new differencing scheme was then developed for the determination of the percentage of hydroxyl minerals in the formation from neutron porosity and gamma-ray-density logs. Changes in full waveform sonic-log power spectra of compressional, shear, Stoneley, and normal mode coda correlate with fracture patterns. Only in the sheeted dikes of Layer 2C could quantitative estimation of the fracture aspect ratio be made; Layers 2A and 2B are too heavily fractured and altered. In the pillow basalts of Layer 2A, there is weak correlation between compressional velocity and degree of alteration, with low sonic velocities appearing to be controlled more by extensive, open fractures. Alteration, rather than fracturing, affects velocity in the heavily altered pillow basalts of Layer 2B, however. Within the dikes of Layer 2C, antiresonance is observed in the spectra of compressional-and shear-wave coda in energies of 30-40 cm wavelengths. A model is developed that treats the medium as highly fractured so that fractures intersect the well bore to form "vents." Antiresonances within the vents are then due to a half-wavelength, vent-resonation system. Using this model, fracture lengths are calculated to average about 25 cm in the dikes. Fracture apertures are observed to be 1 to several mm in diameter from the borehole televiewer.The venting model also accounts for the filter characteristics of the power spectra of the Stoneley and normal mode coda observed in the dike section of Hole 504B. The intervals in which energy levels of Stoneley and normal mode coda are low correlate with zones of intense fracturing observed in the borehole televiewer log. In the highly dispersive normal modes, frequency changes track energy variations. When energy is high in unvented, lightly fractured segments of the borehole, center frequency is high; when energy is dissipated into vents in highly fractured portions of the hole, the center frequency of these low-energy intervals is low as well.In contrast, geophysical logs from Hole 556 in 17-Ma crust on the west flank of the Mid-Atlantic Ridge clearly indicate major alteration and lithology changes within the 177 m of crust penetrated. Hydroxyl-mineral content and M-N cross plots identify pillow basalt, basaltic breccia, and massive basalt zones, as well as gabbro, gabbroic breccia, and serpentinized gabbro layers found at the bottom of the well. Sonic waveforms respond to impedance changes not only from fracturing as in Hole 504B but from alteration and lithology changes as well. Changes in the power spectra appear to be controlled somewhat by alteration. Relatively fresh basalt and gabbro all...

Two component complex tones were synthesized so that each member of a complementary pair exhibited identical amplitude modulations; frequency modulations, however, were in opposite directions. Previous work has shown that the discriminability of the members of a complementary pair is related to the envelope-weighted differences in their instantaneous frequency functions. Listeners report that they base their discriminations upon differences in pitch between complementary two component signals. We assumed that the high discriminability found for moderate separations between the two component frequencies would not obtain if the components were resolved into separate critical bands. Thus we could define the just discriminable (75%) frequency separation as a direct estimate of spectral resolving power without recourse to assumptions about masking effectiveness, loudness summation, or other subjective changes thought to depend upon auditory spectral resolving power. Our findings indicate that resolution bandwidths resulting from the discriminability of complex tone pairs approximate the width of the traveling-wave envelope observed by von Békèsy. In light of our results, the implications for other critical bandwidth estimates are discussed.