Investigating the Utility of a Compact Loudspeaker Array for Audiometric Testing.

Purpose: This project addressed the uses of a loudspeaker array for audiometric measurements. It sought to evaluate a prototype compact array in terms of the reliability of test results across sound booths.

Method: A seven-loudspeaker array was developed to deliver sounds from -60° to +60° on an arc with a radius of 0.

A method for degrading sound localization while preserving binaural advantages for speech reception in noise.

This study developed and tested a real-time processing algorithm designed to degrade sound localization (LocDeg algorithm) without affecting binaural benefits for speech reception in noise. Input signals were divided into eight frequency channels. The odd-numbered channels were mixed between the ears to confuse the direction of interaural cues while preserving interaural cues in the even-numbered channels.

Can monaural temporal masking explain the ongoing precedence effect?

The precedence effect for transient sounds has been proposed to be based primarily on monaural processes, manifested by asymmetric temporal masking. This study explored the potential for monaural explanations with longer ("ongoing") sounds exhibiting the precedence effect. Transient stimuli were single lead-lag noise burst pairs; ongoing stimuli were trains of 63 burst pairs.

Strength of onset and ongoing cues in judgments of lateral position.

This study describes the contributions to auditory image position of an interaural time delay (ITD) cue at onset relative to subsequent ITDs during the ongoing part of a stimulus. Test stimuli were trains of 1-ms binaural noise bursts; lateral position was measured with a wideband acoustic pointer that subjects adjusted to match the intracranial position of test stimuli. In different conditions the ongoing part of the stimulus (the bursts following the first one) either had a consistent ITD (the same ITD on each ongoing burst), or had alternating leading and lagging components with ITDs that opposed one another.

Threshold of the precedence effect in noise.

Three effects that show a temporal asymmetry in the influence of interaural cues were studied through the addition of masking noise: (1) The transient precedence effect-the perceptual dominance of a leading transient over a similar lagging transient; (2) the ongoing precedence effect-lead dominance with lead and lag components that extend in time; and (3) the onset capture effect-determination by an onset transient of the lateral position of an otherwise ambiguous extended trailing sound. These three effects were evoked with noise-burst stimuli and were compared in the presence of masking noise. Using a diotic noise masker, detection thresholds for stimuli with lead/lag interaural delays of 0/500 μs were compared to those with 500/0 μs delays.

Lateralization of noise-burst trains based on onset and ongoing interaural delays.

The lateralization of 250-ms trains of brief noise bursts was measured using an acoustic pointing technique. Stimuli were designed to assess the contribution of the interaural time delay (ITD) of the onset binaural burst relative to that of the ITDs in the ongoing part of the train. Lateralization was measured by listeners' adjustments of the ITD of a pointer stimulus, a 50-ms burst of noise, to match the lateral position of the target train.

Review article: review of the literature on temporal resolution in listeners with cochlear hearing impairment: a critical assessment of the role of suprathreshold deficits.

A critical review of studies of temporal resolution in listeners with cochlear hearing impairment is presented with the aim of assessing evidence for suprathreshold deficits. Particular attention is paid to the roles of variables-such as stimulus audibility, overall stimulus level, and participant's age-which may complicate the interpretation of experimental findings in comparing the performance of hearing-impaired (HI) and normal-hearing (NH) listeners. On certain temporal tasks (e.

Auditory target detection in reverberation.

Measurements and theoretical predictions of auditory target detection in simulated reverberant conditions are reported. The target signals were pulsed 1/3-octave bands of noise and the masker signal was a continuous wideband noise. Target and masker signals were passed through a software simulation of a reverberant room with a rigid sphere modeling a listener's head.

Lateralization of two-transient stimuli.

In this study of the precedence effect in binaural hearing, subjects adjusted the interaural delay of a wideband acoustic pointer to match the perceived intracranial position of transient test stimuli presented over headphones. The test stimuli had leading and lagging components (either brief noise bursts or clicks), each with its own interaural delay. In some test conditions, the leading and lagging stimuli were coherent copies of one another, whereas in others, they were independent samples of noise.

Evaluation of array-processing algorithms for a headband hearing aid.

Several array-processing algorithms were implemented and evaluated with experienced hearing-aid users. The array consisted of four directional microphones mounted broadside on a headband worn on the top of the listener's head. The algorithms included two adaptive array-processing algorithms, one fixed array-processing algorithm, and a reference condition consisting of binaural directional microphones.

Robustness of an Adaptive Beamforming Method for Hearing Aids.

We describe the results of computer simulations of a multimicrophone adaptive-beamforming system as a noise reduction device for hearing aids. Of particular concern was the system's sensitivity to violations of the underlying assumption that the target signal is identical at the microphones. Two-and four-microphone versions of the system were tested in simulated anechoic and modestly-reverberant environments with one and two jammers, and with deviations from the assumed straight-ahead target direction.