Evaluation of the preliminary auditory profile test battery in an international multi-centre study.

OBJECTIVE: This paper describes the composition and international multi-centre evaluation of a battery of tests termed the preliminary auditory profile. It includes measures of loudness perception, listening effort, speech perception, spectral and temporal resolution, spatial hearing, self-reported disability and handicap, and cognition. Clinical applicability and comparability across different centres are investigated. DESIGN: Headphone tests were conducted in five centres divided over four countries. Effects of test-retest, ear, and centre were investigated. Results for normally-hearing (NH) and hearing-impaired (HI) listeners are presented. STUDY SAMPLE: Thirty NH listeners aged 19-39 years, and 72 HI listeners aged 22-91 years with a broad range of hearing losses were included. RESULTS: Test-retest reliability was generally good and there were very few right/left ear effects. Results of all tests were comparable across centres for NH listeners after baseline correction to account for necessary differences between test materials. For HI listeners, results were comparable across centres for the language-independent tests. CONCLUSIONS: The auditory profile forms a clinical test battery that is applicable in four different languages. Even after baseline correction, differences between test materials have to be taken into account when interpreting results of language-dependent tests in HI listeners.

Effects of coarticulation, prosody, and noise freshness on the intelligibility of digit triplets in noise.

BACKGROUND: In a number of European countries, a functional self-test to screen for hearing impairment is available via telephone and the Internet. The tests estimate speech-reception thresholds using an adaptive procedure in which digit triplets are presented at varying signal-to-noise ratios. In different languages, the stimuli were created either with or without coarticulation; and some implementations use fresh noise samples, while others do not. PURPOSE: The present investigation concerns the influence of coarticulation, prosody, and noise freshness on measured thresholds. STUDY SAMPLE: We performed a laboratory study using 12 normal-hearing listeners. RESEARCH DESIGN: In a blocked design we compared speech-reception thresholds for conditions with and without fresh noise tokens. In each block we used three types of triplets: with coarticulation and prosody, with neither, and without coarticulation but with prosody. DATA COLLECTION AND ANALYSIS: Thirty-six thresholds were recorded per subject, and they were analyzed using analyses of variance. RESULTS: The results showed no significant differences among the three triplet conditions. The freshness of the noise did not affect thresholds when, at least, a fresh noise token was used per threshold estimate (23 presentations). Scores dropped significantly when a whole experimental block was performed with a single noise token.

Modeling speech intelligibility in quiet and noise in listeners with normal and impaired hearing.

The speech intelligibility index (SII) is an often used calculation method for estimating the proportion of audible speech in noise. For speech reception thresholds (SRTs), measured in normally hearing listeners using various types of stationary noise, this model predicts a fairly constant speech proportion of about 0.33, necessary for Dutch sentence intelligibility. However, when the SII model is applied for SRTs in quiet, the estimated speech proportions are often higher, and show a larger inter-subject variability, than found for speech in noise near normal speech levels [65 dB sound pressure level (SPL)]. The present model attempts to alleviate this problem by including cochlear compression. It is based on a loudness model for normally hearing and hearing-impaired listeners of Moore and Glasberg [(2004). Hear. Res. 188, 70-88]. It estimates internal excitation levels for speech and noise and then calculates the proportion of speech above noise and threshold using similar spectral weighting as used in the SII. The present model and the standard SII were used to predict SII values in quiet and in stationary noise for normally hearing and hearing-impaired listeners. The present model predicted SIIs for three listener types (normal hearing, noise-induced, and age-induced hearing loss) with markedly less variability than the standard SII.

Effect of inter-phase gap on the sensitivity of cochlear implant users to electrical stimulation.

Human behavioral thresholds for trains of biphasic pulses applied to a single channel of Nucleus CI24 and LAURA cochlear implants were measured as a function of inter-phase gap (IPG). Experiment 1 used bipolar stimulation, a 100-pps pulse rate, and a 400-ms stimulus duration. In one condition, the two phases of each pulse had opposite polarity. Thresholds continued to drop by 9-10 dB as IPG was increased from near zero to the longest value tested (2900 micros for CI24, 4900 micros for LAURA). This time course is much longer than reported for single-cell recordings from animals. In a second condition, the two phases of each pulse had the same polarity, which alternated from pulse to pulse. Thresholds were independent of IPG, and similar to those in condition 1 at IPG=4900 micros. Experiment 2 used monopolar stimulation. One condition was similar to condition 1 of experiment 1, and thresholds also dropped up to the longest IPG studied (2900 micros). This also happened when the pulse rate was reduced to 20 pps, and when only a single pulse was presented on each trial. Keeping IPG constant at 8 micros and adding an extra biphasic pulse x ms into each period produced thresholds that were roughly independent of x, indicating that the effect of IPG in the other conditions was not due to a release from refractoriness at sites central to the auditory nerve. Experiment 3 measured thresholds at three IPGs, which were less than, equal to, and more than one half of the interval between successive pulses. Thresholds were lowest at the intermediate IPG. The results of all experiments could be fit by a linear model consisting of a lowpass filter based on the function relating threshold to the frequency of sinusoidal electrical stimulation. The data and model have implications for reducing the power consumption of cochlear implants.

Cognitive processing load during listening is reduced more by decreasing voice similarity than by increasing spatial separation between target and masker speech.

We investigated changes in speech recognition and cognitive processing load due to the masking release attributable to decreasing similarity between target and masker speech. This was achieved by using masker voices with either the same (female) gender as the target speech or different gender (male) and/or by spatially separating the target and masker speech using HRTFs. We assessed the relation between the signal-to-noise ratio required for 50% sentence intelligibility, the pupil response and cognitive abilities. We hypothesized that the pupil response, a measure of cognitive processing load, would be larger for co-located maskers and for same-gender compared to different-gender maskers. We further expected that better cognitive abilities would be associated with better speech perception and larger pupil responses as the allocation of larger capacity may result in more intense mental processing. In line with previous studies, the performance benefit from different-gender compared to same-gender maskers was larger for co-located masker signals. The performance benefit of spatially-separated maskers was larger for same-gender maskers. The pupil response was larger for same-gender than for different-gender maskers, but was not reduced by spatial separation. We observed associations between better perception performance and better working memory, better information updating, and better executive abilities when applying no corrections for multiple comparisons. The pupil response was not associated with cognitive abilities. Thus, although both gender and location differences between target and masker facilitate speech perception, only gender differences lower cognitive processing load. Presenting a more dissimilar masker may facilitate target-masker separation at a later (cognitive) processing stage than increasing the spatial separation between the target and masker. The pupil response provides information about speech perception that complements intelligibility data.

Effect of frequency-modulation coherence for inharmonic stimuli: frequency-modulation phase discrimination and identification of artificial double vowels.

The ability to compare patterns of frequency modulation (FM) in separate frequency regions was explored. In experiment 1, listeners had to distinguish whether the FM applied to two nonharmonically related sinusoidal carriers was in phase or out of phase. The FM rate was the same for each carrier. The starting phase of the modulation was randomized for each stimulus in a three alternative, forced-choice (3AFC) trial. Subjects were sensitive to relative FM phase for modulation rates of 2 and 4 Hz, but not for higher rates. In experiment 2, vowel identification was compared for artificial single and double vowels. The vowels were constructed from complex tones with components spaced at 2-ERB(N) (equivalent rectangular bandwidth) intervals, by increasing the levels of three components by 15 dB, to create three "formants." In the double vowels, the components of the two vowels were interleaved, to give 1-ERB(N) spacing. The three "formant" components were frequency modulated at 2, 4, or 8 Hz, with either the same or different rates for the two vowels. The identification of double vowels was not improved by a difference in FM rate across vowels, suggesting that differences in FM rate do not support perceptual segregation of inharmonic stimuli.

Automated post-hoc noise cancellation tool for audio recordings acquired in an MRI scanner.

There are several types of experiment in which it is useful to have subjects speak overtly in a magnetic resonance imaging (MRI) scanner, including those studying the articulatory apparatus and the neural basis of speech production, and fMRI experiments in which speech is used as a response modality. Although it is relatively easy to record sound from the bore, it can be difficult to hear the speech over the very loud acoustic noise from the scanner. This is particularly a problem during echo-planar imaging, which is usually used for fMRI. We present a post-hoc sound cancellation algorithm, and describe a Windows-based tool that implements it. The tool is fast and operates with minimal user intervention. We evaluate cancellation performance in terms of the improvement in signal-to-noise ratio, and investigate the effect of the recording medium. A substantial improvement in audibility was obtained.

Methodological aspects of an adaptive multidirectional pattern search to optimize speech perception using three hearing-aid algorithms.

In this study we investigated the reliability and convergence characteristics of an adaptive multidirectional pattern search procedure, relative to a nonadaptive multidirectional pattern search procedure. The procedure was designed to optimize three speech-processing strategies. These comprise noise reduction, spectral enhancement, and spectral lift. The search is based on a paired-comparison paradigm, in which subjects evaluated the listening comfort of speech-in-noise fragments. The procedural and nonprocedural factors that influence the reliability and convergence of the procedure are studied using various test conditions. The test conditions combine different tests, initial settings, background noise types, and step size configurations. Seven normal hearing subjects participated in this study. The results indicate that the reliability of the optimization strategy may benefit from the use of an adaptive step size. Decreasing the step size increases accuracy, while increasing the step size can be beneficial to create clear perceptual differences in the comparisons. The reliability also depends on starting point, stop criterion, step size constraints, background noise, algorithms used, as well as the presence of drifting cues and suboptimal settings. There appears to be a trade-off between reliability and convergence, i.e., when the step size is enlarged the reliability improves, but the convergence deteriorates.