Audiometric thresholds and otoacoustic emissions (OAEs) were measured in 285 U.S. Marine Corps recruits before and three weeks after exposure to impulse-noise sources from weapons' fire and simulated artillery, and in 32 non-noise-exposed controls. At pre-test, audiometric thresholds for all ears were
In a longitudinal study with 338 volunteers, audiometric thresholds and otoacoustic emissions were measured before and after 6 months of noise exposure on an aircraft carrier. While the average amplitudes of the otoacoustic emissions decreased significantly, the average audiometric thresholds did not change. Furthermore, there were no significant correlations between changes in audiometric thresholds and changes in otoacoustic emissions. Changes in transient-evoked otoacoustic emissions and distortion-product otoacoustic emissions were moderately correlated. Eighteen ears acquired permanent audiometric threshold shifts. Only one-third of those ears showed significant otoacoustic emission shifts that mirrored their permanent threshold shifts. A Bayesian analysis indicated that permanent threshold shift status following a deployment was predicted by baseline low-level or absent otoacoustic emissions. The best predictor was transient-evoked otoacoustic emission amplitude in the 4-kHz half-octave frequency band, with risk increasing more than sixfold from approximately 3% to 20% as the emission amplitude decreased. It is possible that the otoacoustic emissions indicated noise-induced changes in the inner ear, undetected by audiometric tests. Otoacoustic emissions may therefore be a diagnostic predictor for noise-induced-hearing-loss risk.
While many psychoacoustic studies have found that listeners can recover some causal properties of sound-generating objects (such as the material), comparatively little is known about the causal properties of the sound-generating actions and how they are perceived. This article reports on a study comparing the performance of listeners required to identify either the actions or the materials used to generate sound stimuli. Stimuli were recordings of a set of cylinders of two sizes and four materials (wood, plastic, glass, metal) undergoing four different actions (scraping, rolling, hitting, bouncing). Experiment 1 tested how well each sound conveyed that it was generated with a different action or material. Experiment 2 measured both accuracy and reaction times for the identification of actions and materials. Listeners were faster and more accurate at identifying the action than the material. Even for the subset of sounds for which actions and materials were equivalently well identified, listeners were faster at identifying the action than the material. These results suggest that the auditory system is well-suited to extract information about sound-generating actions.
Sensitivity to interaural time delays (ITDs) within high-frequency sinusoidally amplitude-modulated (SAM) target tones was measured in the presence of a second, spectrally remote diotic SAM tone (termed an interferer). Targets and interferers were 100% modulated at 250 Hz and each was presented at 77 dB SPL for a duration of 250 ms. The modulations of targets and interferers were either in-phase or out-of-phase. In the first experiment, when the target SAM tone was centered at 4 kHz, interferers were centered at either 500 Hz, 1 kHz, or 2 kHz. Threshold ITDs were substantially increased in the presence of the interferers as compared to when the targets were presented in isolation. The greatest effects were observed with interferers centered at 500 Hz and 1 kHz. In the second experiment, when the target SAM tone was centered at 2 kHz, interferers were centered at either 500 Hz or 4 kHz. Threshold ITDs increased in the presence of either interferer, but the greatest increase occurred in the presence of the 500-Hz SAM tone. In the third experiment, it was found that presenting the low-frequency SAM tones continuously resulted in less interference than did presenting the interferers and targets coincidently. In all three experiments, the effects produced by the interferers did not depend upon whether they were modulated in-phase or out-of-phase with the target. Taken together, the data argue against the notion that the interference could result from a peripheral, monaural interaction between target and interferer waveforms.
Extents of laterality produced by ongoing interaural time delays (ITDs) within high-frequency sinusoidally amplitude-modulated (SAM) target tones were measured in the presence or absence of a second, spectrally remote, diotic, SAM tone. The spectrally remote SAM tones had recently been shown to reduce sensitivity to ITDs conveyed by a 4-kHz SAM tone in a previous experiment employing the same listeners [L. M. Heller and C. Trahiotis, J. Acoust. Soc. Am. 97, 1808–1816 (1995)]. All SAM tones were 100% modulated at 250 Hz and were presented at 77 dB SPL for a duration of 250 ms. The SAM target tone was centered at 4 kHz and the lower-frequency SAM tones were centered at either 500 Hz, 1 kHz, or 2 kHz. The data indicate that spectrally remote, diotic, SAM tones ‘‘pull’’ the lateral position of a 4-kHz SAM tone toward the midline, even when the 4-kHz SAM tone contains an ITD of up to 400 or 600 μs. This means that effects of spectrally remote information are not confined to tasks which require that listeners detect, or discriminate between, threshold amounts of ITD. Analyses revealed that changes in lateral position, as measured by an acoustic pointing task, cannot in and of themselves account for the interference effects found in discrimination tasks with similar stimuli. It was found, however, that Buell and Hafter’s [J. Acoust. Soc. Am. 90, 1894–1900 (1991)] weighted-combination model, when augmented to include measures of laterality as well as measures of discriminability, could provide reasonably accurate predictions of the amounts of interference obtained in the discrimination task.
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