The Sensitivity of Hearing-Impaired Adults to Acoustic Attributes in Simulated Rooms

In previous studies we have shown that older hearing-impaired individuals are relatively insensitive to changes in the apparent width of broadband noises when those width changes were based on differences in interaural coherence [W. Whitmer, B. Seeber and M. Akeroyd, J. Acoust. Soc. Am. 132, 369-379 (2012)]. This insensitivity has been linked to senescent difficulties in resolving binaural fine-structure differences. It is therefore possible that interaural coherence, despite its widespread use, may not be the best acoustic surrogate of spatial perception for the aged and impaired. To test this, we simulated the room impulse responses for various acoustic scenarios with differing coherence and lateral (energy) fraction attributes using room modelling software (ODEON). Bilaterally impaired adult participants were asked to sketch the perceived size of speech tokens and musical excerpts that were convolved with these impulse responses and presented to them in a sound-dampened enclosure through a 24-loudspeaker array. Participants' binaural acuity was also measured using an interaural phase discrimination task. Corroborating our previous findings, the results showed less sensitivity to interaural coherence in the auditory source width judgments of older hearing-impaired individuals, indicating that alternate acoustic measurements in the design of spaces for the elderly may be necessary

The effect of hearing aid microphone mode on performance in an auditory orienting task

OBJECTIVES: Although directional microphones on a hearing aid provide a signal-to-noise ratio benefit in a noisy background, the amount of benefit is dependent on how close the signal of interest is to the front of the user. It is assumed that when the signal of interest is off-axis, users can reorient themselves to the signal to make use of the directional microphones to improve signal-to-noise ratio. The present study tested this assumption by measuring the head-orienting behavior of bilaterally fit hearing-impaired individuals with their microphones set to omnidirectional and directional modes. The authors hypothesized that listeners using directional microphones would have greater difficulty in rapidly and accurately orienting to off-axis signals than they would when using omnidirectional microphones. DESIGN: The authors instructed hearing-impaired individuals to turn and face a female talker in simultaneous surrounding male-talker babble. Participants pressed a button when they felt they were accurately oriented in the direction of the female talker. Participants completed three blocks of trials with their hearing aids in omnidirectional mode and three blocks in directional mode, with mode order randomized. Using a Vicon motion tracking system, the authors measured head position and computed fixation error, fixation latency, trajectory complexity, and proportion of misorientations. RESULTS: Results showed that for larger off-axis target angles, listeners using directional microphones took longer to reach their targets than they did when using omnidirectional microphones, although they were just as accurate. They also used more complex movements and frequently made initial turns in the wrong direction. For smaller off-axis target angles, this pattern was reversed, and listeners using directional microphones oriented more quickly and smoothly to the targets than when using omnidirectional microphones. CONCLUSIONS: The authors argue that an increase in movement complexity indicates a switch from a simple orienting movement to a search behavior. For the most off-axis target angles, listeners using directional microphones appear to not know which direction to turn, so they pick a direction at random and simply rotate their heads until the signal becomes more audible. The changes in fixation latency and head orientation trajectories suggest that the decrease in off-axis audibility is a primary concern in the use of directional microphones, and listeners could experience a loss of initial target speech while turning toward a new signal of interest. If hearing-aid users are to receive maximum directional benefit in noisy environments, both adaptive directionality in hearing aids and clinical advice on using directional microphones should take head movement and orientation behavior into account

The effect of experience on the sensitivity and specificity of the whispered voice test: a diagnostic accuracy study

Objectives: To determine the sensitivity and specificity of the whispered voice test (WVT) in detecting hearing loss when administered by practitioners with different levels of experience.<p></p> Design: Diagnostic accuracy study of WVT, through acoustic analysis of whispers of experienced and inexperienced practitioners (experiment 1) and behavioural validation of these recordings (experiment 2).<p></p> Setting: Research institute with a pool of patients sourced from local clinics in the Greater Glasgow area.<p></p> Participants: 22 people had their whispers recorded and analysed in experiment 1; 4 older experienced (OE), 4 older inexperienced (OI) and 14 younger inexperienced (YI). In experiment 2, 73 people (112 individual ears) took part in a digit recognition task using 2 OE and 2 YI whisperers from experiment 1.<p></p> Main outcome measures: Average level (dB sound pressure level) across frequency, average level across all utterances (dB A) and within/across-digit deviation (dB A) for experiment 1. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of WVT for experiment 2.<p></p> Results: In experiment 1, OE whisperers were 8–10 dB more intense than inexperienced whisperers across all whispered utterances. Variability was low and comparable regardless of age or experience. In experiment 2, at an optimum threshold of 40 dB HL, sensitivity and specificity were 63% (95% CI of 58% to 68%) and 93% (92% to 94%), respectively, for OE whisperers. PPV was 56% (51% to 61%), NPV was 95% (94% to 96%). For YI whisperers at an optimum threshold of 29 dB HL, sensitivity and specificity were 80% (78% to 82%) and 52% (50% to 55%), respectively. PPV was 65% (63% to 67%) and NPV was 70% (67% to 72%).<p></p> Conclusions: WVT is an effective screening test, providing the level of the whisperer is considered when setting the test's hearing-loss criterion. Possible implications are voice measurement while training for inexperienced whisperers.<p></p

Changes in orientation behavior due to extended high-frequency (5-10 kHz) spatial cues

Objectives: Current hearing aids have a limited bandwidth, which limits the intelligibility and quality of their output, and inhibits their uptake. Recent advances in signal processing, as well as novel methods of transduction, allow for a greater useable frequency range. Previous studies have shown a benefit for this extended bandwidth in consonant recognition, talker-sex identification, and separating sound sources. To explore whether there would be any direct spatial benefits to extending bandwidth, we used a dynamic localization method in a realistic situation. Design: Twenty-eight adult participants with minimal hearing loss reoriented themselves as quickly and accurately as comfortable to a new, off-axis near-field talker continuing a story in a background of far-field talkers of the same overall level in a simulated large room with common building materials. All stimuli were low-pass filtered at either 5 or 10 kHz on each trial. To further simulate current hearing aids, participants wore microphones above the pinnae and insert earphones adjusted to provide a linear, zero-gain response. Results: Each individual trajectory was recorded with infra-red motion-tracking and analyzed for accuracy, duration, start time, peak velocity, peak velocity time, complexity, reversals, and misorientations. Results across listeners showed a significant increase in peak velocity and significant decrease in start and peak velocity time with greater (10 kHz) bandwidth. Conclusions: These earlier, swifter orientations demonstrate spatial benefits beyond static localization accuracy in plausible conditions; extended bandwidth without pinna cues provided more salient cues in a realistic mixture of talkers

Auditory and visual orienting responses in listeners with and without hearing-impairment

Head movements are intimately involved in sound localization and may provide information that could aid an impaired auditory system. Using an infrared camera system, head position and orientation was measured for 17 normal-hearing and 14 hearing-impaired listeners seated at the center of a ring of loudspeakers. Listeners were asked to orient their heads as quickly as was comfortable toward a sequence of visual targets, or were blindfolded and asked to orient toward a sequence of loudspeakers playing a short sentence. To attempt to elicit natural orienting responses, listeners were not asked to reorient their heads to the 0 degrees loudspeaker between trials. The results demonstrate that hearing-impairment is associated with several changes in orienting responses. Hearing-impaired listeners showed a larger difference in auditory versus visual fixation position and a substantial increase in initial and fixation latency for auditory targets. Peak velocity reached roughly 140 degrees/s in both groups, corresponding to a rate of change of approximately 1 mu s of interaural time difference per millisecond of time. Most notably, hearing-impairment was associated with a large change in the complexity of the movement, changing from smooth sigmoidal trajectories to ones characterized by abruptly changing velocities, directional reversals, and frequent fixation angle corrections

Undirected head movements of listeners with asymmetrical hearing impairment during a speech-in-noise task

It has long been understood that the level of a sound at the ear is dependent on head orientation, but the way in which listeners move their heads during listening has remained largely unstudied. Given the task of understanding a speech signal in the presence of a simultaneous noise, listeners could potentially use head orientation to either maximize the level of the signal in their better ear, or to maximize the signal-to-noise ratio in their better ear. To establish what head orientation strategy listeners use in a speech comprehension task, we used an infrared motion-tracking system to measure the head movements of 36 listeners with large (>16 dB) differences in hearing threshold between their left and right ears. We engaged listeners in a difficult task of understanding sentences presented at the same time as a spatially separated background noise. We found that they tended to orient their heads so as to maximize the level of the target sentence in their better ear, irrespective of the position of the background noise. This is not ideal orientation behavior from the perspective of maximizing the signal-to-noise ratio (SNR) at the ear, but is a simple, easily implemented strategy that is often effective in an environment where the spatial position of multiple noise sources may be difficult or impossible to determine