Further Evaluation of a Protocol for Integrated Speech Audiometry.

PURPOSE: When a bilateral evaluation is conducted with the integrated speech protocol described in Punch and Rakerd (2019), testing for the first ear concludes with a measurement of the uncomfortable loudness level for speech (UCL). The purpose of this study was to assess the possibility that exposure to the high speech intensities required for that UCL test might bias the subsequent measurement of a listener's most comfortable loudness level for speech (MCL) in the opposite ear. METHOD: Across 32 test runs, the left and right ear MCLs were established for 16 young adult listeners with normal hearing (five women, 11 men). The MCL assessed on each test run was measured twice. The first measurement was made at the start of the run and before a full integrated speech evaluation was conducted in the opposite ear (pretest); the second was made after that evaluation (posttest). RESULTS: The difference between the MCL means measured on the pretest (37.7 dB) and the posttest (38.5 dB) was less than 1 dB, and it did not approach statistical significance, t(15) = 0.69, p = .50. CONCLUSIONS: There was no evidence that UCL testing done in one ear on a bilateral speech test will have carryover effects that bias the subsequent measurement of a listener's MCL in the other ear. The results, therefore, support the potential clinical use of an integrated protocol when conducting bilateral speech audiometric evaluations.

Ferroelectret Nanogenerators for Loudspeaker Applications: A Comprehensive Study.

A ferroelectret nanogenerator (FENG) was recently developed as a flexible energy harvesting device with bi-directional capability between electrical and mechanical energy domains, and its use as a loudspeaker/microphone was demonstrated. Dependencies of Sound Pressure Levels (SPLs) generated by FENG due to an AC voltage stimulus, surface area, geometric shape, and addition of layers are presented here. Also, the relation between the sound output to the electrical input is studied and shown to be linear, which demonstrates that these flexible loudspeakers have low distortion within the human audible range of 20 Hz to 20 kHz. A study for ultrasonic frequencies up to 40 kHz is also presented. A theoretical model relating the electrical and acoustical domain of the FENG is developed based on the experimental observations made and using Boundary Element Methods (BEM) to accurately mimic the testing environment for simulation purposes. The comparison between this model and the actual behavior is presented under several cases and observed to be closely correlated.

Evaluation of a Protocol for Integrated Speech Audiometry.

Purpose This project was aimed at evaluating the reliability, validity, and clinical utility of a protocol for integrated measurements of the most comfortable level (MCL) and uncomfortable level (UCL) for speech, in combination with the speech recognition threshold (SRT). We also evaluated the validity of using spondee words when measuring speech MCL and UCL. Method In a randomized block design, equal numbers of women and men with normal hearing, aged 18-29 years, were assigned to each of 3 experimental stimulus conditions: spondee singlets, spondee triplets, or connected discourse ( n = 12 per group). Following measurement of the SRT, a modified method of limits was employed to establish, on a 7-point loudness rating scale, an ascending MCL, a descending MCL, and an ascending UCL. A single instructional set covered all loudness measurements. Test times were tracked electronically to assess clinical efficiency. All test conditions were repeated during each of 2 separate test sessions. Results Mean SRTs, MCLs, and UCLs across the 3 different experimental groups were found not to differ statistically or clinically (mean differences < 5 dB). Intrasession and intersession reliability for the various measures were excellent, and testing of all listeners was completed in a timely manner. In a follow-up experiment with adults with normal hearing who were only a decade older than participants in our main experiment, the older group was found to have significantly higher MCLs and UCLs. Conclusions Spondee words can be used routinely to obtain reliable, valid, and clinically efficient measures of MCLs and UCLs for speech, in a protocol combined with the SRT. Spondees, presented singly, yielded the greatest level of efficiency overall. Results support a recommendation to obtain an ascending measurement of MCL prior to a descending measurement and to establish the MCL by averaging the 2 values.

Resonance Effects and the Vocalization of Speech.

Studies of the respiratory and laryngeal actions required for phonation are central to our understanding of both voice and voice disorders. The purpose of the present article is to highlight complementary insights about voice that have come from the study of vocal tract resonance effects.

Assessing the Acoustic Characteristics of Rooms: A Tutorial with Examples.

In both practicing audiology and speech language pathology, as well as in speech and hearing science research, the space where the work is done is an integral part of the function. Hence, for all of these endeavors it can be important to measure the acoustics of a room. This article provides a tutorial regarding the measurement of room reverberation and background noise, both of which are important when evaluating a space's strengths and limitations for speech communication. As the privacy of patients and research participants is a primary concern, the tutorial also describes a method for measuring the amount of acoustical insulation provided by a room's barriers. Several room measurement data sets - all obtained from the assessment of clinical and research spaces within our own department - are presented here as examples.

On the localization of high-frequency, sinusoidally amplitude-modulated tones in free field.

Previous headphone experiments have shown that listeners can lateralize high-frequency sine-wave amplitude-modulated (SAM) tones based on interaural time differences in the envelope. However, when SAM tones are presented to listeners in free field or in a room, diffraction by the head or reflections from room surfaces alter the modulation percentages and change the shapes of the envelopes, potentially degrading the envelope cue. Amplitude modulation is transformed into mixed modulation. This article presents a mathematical transformation between the six spectral parameters for a modulated tone and six mixed-modulation parameters for each ear. The transformation was used to characterize the stimuli in the ear canals of listeners in free-field localization experiments. The mixed modulation parameters were compared with the perceived changes in localization attributable to the modulation for five different listeners, who benefited from the modulation to different extents. It is concluded that individual differences in the response to added modulation were not systematically related to the physical modulation parameters themselves. Instead, they were likely caused by individual differences in processing of envelope interaural time differences.

Transaural experiments and a revised duplex theory for the localization of low-frequency tones.

The roles of interaural time difference (ITD) and interaural level difference (ILD) were studied in free-field source localization experiments for sine tones of low frequency (250-750 Hz). Experiments combined real-source trials with virtual trials created through transaural synthesis based on real-time ear canal measurements. Experiments showed the following: (1) The naturally occurring ILD is physically large enough to exert an influence on sound localization well below 1000 Hz. (2) An ILD having the same sign as the ITD modestly enhances the perceived azimuth of tones for all values of the ITD, and it eliminates left-right confusions that otherwise occur when the interaural phase difference (IPD) passes 180°. (3) Increasing the ILD to large, implausible values can decrease the perceived laterality while also increasing front-back confusions. (4) Tone localization is more directly related to the ITD than to the IPD. (5) An ILD having a sign opposite to the ITD promotes a slipped-cycle ITD, sometimes with dramatic effects on localization. Because the role of the ITD itself is altered by the ILD, the duplex processing of ITD and ILD reflects more than mere trading; the effect of the ITD can be reversed in sign.

Computing interaural differences through finite element modeling of idealized human heads.

Acoustical interaural differences were computed for a succession of idealized shapes approximating the human head-related anatomy: sphere, ellipsoid, and ellipsoid with neck and torso. Calculations were done as a function of frequency (100-2500 Hz) and for source azimuths from 10 to 90 degrees using finite element models. The computations were compared to free-field measurements made with a manikin. Compared to a spherical head, the ellipsoid produced greater large-scale variation with frequency in both interaural time differences and interaural level differences, resulting in better agreement with the measurements. Adding a torso, represented either as a large plate or as a rectangular box below the neck, further improved the agreement by adding smaller-scale frequency variation. The comparisons permitted conjectures about the relationship between details of interaural differences and gross features of the human anatomy, such as the height of the head, and length of the neck.

Localization of sound in rooms. V. Binaural coherence and human sensitivity to interaural time differences in noise.

Binaural recordings of noise in rooms were used to determine the relationship between binaural coherence and the effectiveness of the interaural time difference (ITD) as a cue for human sound localization. Experiments showed a strong, monotonic relationship between the coherence and a listener's ability to discriminate values of ITD. The relationship was found to be independent of other, widely varying acoustical properties of the rooms. However, the relationship varied dramatically with noise band center frequency. The ability to discriminate small ITD changes was greatest for a mid-frequency band. To achieve sensitivity comparable to mid-band, the binaural coherence had to be much larger at high frequency, where waveform ITD cues are imperceptible, and also at low frequency, where the binaural coherence in a room is necessarily large. Rivalry experiments with opposing interaural level differences (ILDs) found that the trading ratio between ITD and ILD increasingly favored the ILD as coherence decreased, suggesting that the perceptual weight of the ITD is decreased by increased reflections in rooms.

The acoustical bright spot and mislocalization of tones by human listeners.

Listeners attempted to localize 1500-Hz sine tones presented in free field from a loudspeaker array, spanning azimuths from 0 degrees (straight ahead) to 90 degrees (extreme right). During this task, the tone levels and phases were measured in the listeners' ear canals. Because of the acoustical bright spot, measured interaural level differences (ILD) were non-monotonic functions of azimuth with a maximum near 55 degrees . In a source-identification task, listeners' localization decisions closely tracked the non-monotonic ILD, and thus became inaccurate at large azimuths. When listeners received training and feedback, their accuracy improved only slightly. In an azimuth-discrimination task, listeners decided whether a first sound was to the left or to the right of a second. The discrimination results also reflected the confusion caused by the non-monotonic ILD, and they could be predicted approximately by a listener's identification results. When the sine tones were amplitude modulated or replaced by narrow bands of noise, interaural time difference (ITD) cues greatly reduced the confusion for most listeners, but not for all. Recognizing the important role of the bright spot requires a reevaluation of the transition between the low-frequency region for localization (mainly ITD) and the high-frequency region (mainly ILD).

Release from speech-on-speech masking in a front-and-back geometry.

Informational masking of a target female talker by female distracters was measured with target and distracters presented from directly in front of the listener as a baseline condition. Next, it was found that if the distracters were also presented from directly in back of the listener, advanced or delayed by a few milliseconds with respect to the distracters in front, release from informational masking occurred. Release from informational masking was found for all delays within the Haas region of +/-50 ms, with peak release of about 3.5 dB. This peak occurred for a delay of +/-2 ms and it was shown to be the result of delay-and-add filtering. Release from energetic masking was also found, but only for delays of +/-0.5 ms or less.

Speech-clarity judgments of hearing-aid-processed speech in noise: differing polar patterns and acoustic environments.

This investigation assessed the extent to which listeners' preferences for hearing aid microphone polar patterns vary across listening environments, and whether normal-hearing and inexperienced and experienced hearing-impaired listeners differ in such preferences. Paired-comparison judgments of speech clarity (i.e. subjective speech intelligibility) were made monaurally for recordings of speech in noise processed by a commercially available hearing aid programmed with an omnidirectional and two directional polar patterns (cardioid and hypercardioid). Testing environments included a sound-treated room, a living room, and a classroom. Polar-pattern preferences were highly reliable and agreed closely across all three groups of listeners. All groups preferred listening in the sound-treated room over listening in the living room, and preferred listening in the living room over listening in the classroom. Each group preferred the directional patterns to the omnidirectional pattern in all room conditions. We observed no differences in preference judgments between the two directional patterns or between hearing-impaired listeners' extent of amplification experience. Overall, findings indicate that listeners perceived qualitative benefits from microphones having directional polar patterns.

Release from speech-on-speech masking by adding a delayed masker at a different location.

The amount of masking exerted by one speech sound on another can be reduced by presenting the masker twice, from two different locations in the horizontal plane, with one of the presentations delayed to simulate an acoustical reflection. Three experiments were conducted on various aspects of this phenomenon. Experiment 1 varied the number of masking talkers from one to three and the signal-to-noise (S/N) ratio from -12 to +4 dB. Evidence of masking release was found for every combination of these variables tested. For the most difficult conditions (multiple maskers and negative S/N) the amount of release was approximately 10 dB. Experiment 2 varied the timing of leading and lagging masker presentations over a broad range, to include shorter delay times where room reflections of speech are rarely noticed by listeners and longer delays where reflections can become disruptive. Substantial masking release was found for all of the shorter delay times tested, and negligible release was found at the longer delays. Finally, Experiment 3 used speech-spectrum noise as a masker and searched for possible energetic masking release as a function of the lead-lag time delay. Release of up to 4 dB was found whenever delays were 2 ms or less. No energetic masking release was found at longer delays.

Most comfortable and uncomfortable loudness levels: six decades of research.

This article critically reviews the influence of such factors as psychophysical testing method, stimulus type, and instructional set on most comfortable loudness (MCL) and uncomfortable loudness (UCL) levels. Generally, research indicates that test methods and instructions strongly affect both MCL and UCL while stimulus conditions affect them less substantially. Overall, the data suggest lower reliability for MCL than for UCL and lower reliability for pure-tone MCLs than for speech MCLs. Lower MCLs are typically obtained when measured by an ascending approach, in contrast to a descending approach. Results suggest that audiological efforts should be directed toward the development of a standardized test procedure that yields adequately reliable and valid MCLs and UCLs for routine clinical use.

Effects of test order on most comfortable and uncomfortable loudness levels for speech.

This study examined test-order effects on most comfortable loudness (MCL) and uncomfortable loudness (UCL) levels for spondaic words in 2 groups of 30 normal hearing listeners each. For Group 1, MCL was measured first, followed by UCL. For Group 2, UCL was measured first, and then MCL. A retest was conducted for both groups. Results showed that MCL was significantly elevated for Group 2, but not for Group 1. There was no effect on UCL for either group. In a follow-up experiment, the magnitude of the test-order effect on MCL increased significantly when MCL measurements followed UCL measurements closely in time. These results argue for management of the ordering and temporal spacing of MCL and UCL testing in clinical loudness measurements.