Psychoacoustics publications

A common method for measuring changes in temporal processing sensitivity in both humans and animals makes use of GaP-induced Inhibition of the Acoustic Startle (GPIAS). It is also the basis of a common method for detecting tinnitus in rodents. However, the link to tinnitus has not been properly established because GPIAS has not yet been used to objectively demonstrate tinnitus in humans. In guinea pigs, the Preyer (ear flick) myogenic reflex is an established method for measuring the acoustic startle for the GPIAS test, while in humans, it is the eye-blink reflex. Yet, humans have a vestigial remnant of the Preyer reflex, which can be detected by measuring skin surface potentials associated with the Post-Auricular Muscle Response (PAMR). A similar electrical potential can be measured in guinea pigs and we aimed to show that the PAMR could be used to demonstrate GPIAS in both species. In guinea pigs, we compare the GPIAS measured using the pinna movement of the Preyer reflex and the electrical potential of the PAMR to demonstrate that the two are at least equivalent. In humans, we establish for the first time that the PAMR provides a reliable way of measuring GPIAS that is a pure acoustic alternative to the multimodal eye-blink reflex. Further exploratory tests showed that while eye gaze position influenced the size of the PAMR response, it did not change the degree of GPIAS. Our findings confirm that the PAMR is a sensitive method for measuring GPIAS and suggest that it may allow direct comparison of temporal processing between humans and animals and may provide a basis for an objective test of tinnitus.

Background: The perception of pediatric voice quality has been investigated using clinical protocols developed for adult voices and acoustic analyses designed to identify important physical parameters associated with normal and dysphonic pediatric voices. Laboratory investigations of adult dysphonia have included sophisticated methods, including a psychoacoustic approach that involves a single-variable matching task (SVMT), characterized by high inter- and intra-listener reliability, and analyses that include bio-inspired models of auditory perception that have provided valuable information regarding adult voice quality. Objectives: To establish the utility of a psychoacoustic approach to the investigation of voice quality perception in the context of pediatric voices? Methods: Six listeners judged the breathiness of 20 synthetic vowel stimuli using an SVMT. To support comparisons with previous data, stimuli were modeled after four pediatric speakers and synthesized using Klatt with five parameter settings that influence the perception of breathiness. The population average breathiness judgments were modeled with acoustic measures of loudness ratio, pitch strength, and cepstral peak. Results: Listeners reliably judged the perceived breathiness of pediatric voices, as with previous investigations of breathiness in adult dysphonic voices. Breathiness judgments were accurately modeled by loudness ratio (r2 = 0.93), pitch strength (r2 = 0.91), and cepstral peak (r2 = 0.82). Model accuracy was not affected significantly by including stimulus fundamental frequency and was slightly higher for pediatric than for adult voices. Conclusions: The SVMT proved robust for pediatric voices spanning a wide range of breathiness. The data indicate that this is a promising approach for future investigation of pediatric voice quality.

Differences in ear of presentation and level do not prevent effective integration of concurrent speech cues such as formant frequencies. For example, presenting the higher formants of a consonant-vowel syllable in the opposite ear to the first formant protects them from upward spread of masking, allowing them to remain effective speech cues even after substantial attenuation. This study used three-formant (F1+F2+F3) analogues of natural sentences and extended the approach to include competitive conditions. Target formants were presented dichotically (F1+F3; F2), either alone or accompanied by an extraneous competitor for F2 (i.e., F1±F2C+F3; F2) that listeners must reject to optimize recognition. F2C was created by inverting the F2 frequency contour and using the F2 amplitude contour without attenuation. In experiment 1, F2C was always absent and intelligibility was unaffected until F2 attenuation exceeded 30 dB; F2 still provided useful information at 48-dB attenuation. In experiment 2, attenuating F2 by 24 dB caused considerable loss of intelligibility when F2C was present, but had no effect in its absence. Factors likely to contribute to this interaction include informational masking from F2C acting to swamp the acoustic-phonetic information carried by F2, and interaural inhibition from F2C acting to reduce the effective level of F2.

Skill learning is fundamental to the acquisition of many complex behaviors that emerge during development. For example, years of practice give rise to perceptual improvements that contribute to mature speech and language skills. While fully honed learning skills might be thought to offer an advantage during the juvenile period, the ability to learn actually continues to develop through childhood and adolescence, suggesting that the neural mechanisms that support skill learning are slow to mature. To address this issue, we asked whether the rate and magnitude of perceptual learning varies as a function of age as male and female gerbils trained on an auditory task. Adolescents displayed a slower rate of perceptual learning compared with their young and mature counterparts. We recorded auditory cortical neuron activity from a subset of adolescent and adult gerbils as they underwent perceptual training. While training enhanced the sensitivity of most adult units, the sensitivity of many adolescent units remained unchanged, or even declined across training days. Therefore, the average rate of cortical improvement was significantly slower in adolescents compared with adults. Both smaller differences between sound-evoked response magnitudes and greater trial-to-trial response fluctuations contributed to the poorer sensitivity of individual adolescent neurons. Together, these findings suggest that elevated sensory neural variability limits adolescent skill learning. SIGNIFICANCE STATEMENT The ability to learn new skills emerges gradually as children age. This prolonged development, often lasting well into adolescence, suggests that children, teens, and adults may rely on distinct neural strategies to improve their sensory and motor capabilities. Here, we found that practice-based improvement on a sound detection task is slower in adolescent gerbils than in younger or older animals. Neural recordings made during training revealed that practice enhanced the sound sensitivity of adult cortical neurons, but had a weaker effect in adolescents. This latter finding was partially explained by the fact that adolescent neural responses were more variable than in adults. Our results suggest that one mechanistic basis of adult-like skill learning is a reduction in neural response variability.

The brain estimates the two-dimensional direction of sounds from the pressure-induced displacements of the eardrums. Accurate localization along the horizontal plane (azimuth angle) is enabled by binaural difference cues in timing and intensity. Localization along the vertical plane (elevation angle), including frontal and rear directions, relies on spectral cues made possible by the elevation dependent filtering in the idiosyncratic pinna cavities. However, the problem of extracting elevation from the sensory input is ill-posed, since the spectrum results from a convolution between source spectrum and the particular head-related transfer function (HRTF) associated with the source elevation, which are both unknown to the system. It is not clear how the auditory system deals with this problem, or which implicit assumptions it makes about source spectra. By varying the spectral contrast of broadband sounds around the 6–9 kHz band, which falls within the human pinna’s most prominent elevation-related spectral notch, we here suggest that the auditory system performs a weighted spectral analysis across different frequency bands to estimate source elevation. We explain our results by a model, in which the auditory system weighs the different spectral bands, and compares the convolved weighted sensory spectrum with stored information about its own HRTFs, and spatial prior assumptions.

Hearing loss has been implicated as a risk factor for schizophrenia, but it is not known whether this association arises from common etiology, top-down influences (e.g., social isolation), bottom-up neurobiological mechanisms, or combinations of these factors. Patients with 22q11.2 Deletion Syndrome (22q11.2DS) have a 25-30% risk of developing schizophrenia, and also suffer frequent hearing loss. Here, we used the Df1 /+ mouse model of 22q11.2DS to investigate the relationship between hearing loss and susceptibility to schizophrenia-relevant brain and behavioral abnormalities. Df1 /+ mice have a multi-gene deletion analogous to the chromosomal microdeletion that causes human 22q11.2DS, and like human 22q11.2DS patients exhibit high rates of hearing loss arising primarily from susceptibility to middle ear inflammation. We found that hearing loss in Df1 /+ mice affected schizophrenia-relevant endophenotypes, including electrophysiological measures of central auditory gain and behavioral measures of auditory sensorimotor gating. Moreover, PV+ inhibitory interneurons, another marker for schizophrenia pathology, were significantly reduced in density in auditory cortex but not secondary motor cortex of Df1 /+ mice with hearing loss. These results reveal bottom-up neurobiological mechanisms through which peripheral hearing loss arising from the 22q11.2 deletion may promote the emergence of schizophrenia-relevant auditory brain and behavioral abnormalities, and also suggest a link between conductive hearing loss and reduced PV+ interneuron density in the auditory cortex. SIGNIFICANCE STATEMENT Hearing loss is a known risk factor for schizophrenia. Deletion of chromosomal locus 22q11.2 is associated with both schizophrenia and hearing loss in humans. In the Df1 /+ mouse model of human 22q11.2 Deletion Syndrome, we find that hearing loss shapes measures that are considered schizophrenia-relevant endophenotypes, such as central auditory gain and auditory sensorimotor gating. Moreover, we report a reduction in density of PV+ inhibitory interneurons in the auditory cortex, but not secondary motor cortex, of Df1 /+ mice with hearing loss. These results suggest mechanisms through which hearing loss associated with the 22q11.2 deletion may promote emergence of schizophrenia-relevant auditory brain and behavioral abnormalities and indicate that conductive hearing loss may influence PV+ interneuron density in the auditory cortex.

Speech audiometry is an essential part of audiological diagnostics and clinical measurements. Development times of speech recognition tests are rather long, depending on the size of speech corpus and optimization necessity. The aim of this study was to examine whether this development effort could be reduced by using synthetic speech in speech audiometry, especially in a matrix test for speech recognition. For this purpose, the speech material of the German matrix test was replicated using a preselected commercial system to generate the synthetic speech files. In contrast to the conventional matrix test, no level adjustments or optimization tests were performed while producing the synthetic speech material. Evaluation measurements were conducted by presenting both versions of the German matrix test (with natural or synthetic speech), alternately and at three different signal-to-noise ratios, to 48 young, normal-hearing participants. Psychometric functions were fitted to the empirical data. Speech recognition thresholds were 0.5 dB signal-to-noise ratio higher (worse) for the synthetic speech, while slopes were equal for both speech types. Nevertheless, speech recognition scores were comparable with the literature and the threshold difference lay within the same range as recordings of two different natural speakers. Although no optimization was applied, the synthetic-speech signals led to equivalent recognition of the different test lists and word categories. The outcomes of this study indicate that the application of synthetic speech in speech recognition tests could considerably reduce the development costs and evaluation time. This offers the opportunity to increase the speech corpus for speech recognition tests with acceptable effort.

Bilateral cochlear-implant (CI) users and single-sided deaf listeners with a CI are less effective at localizing sounds than normal-hearing (NH) listeners. This performance gap is due to the degradation of binaural and monaural sound localization cues, caused by a combination of device-related and patient-related issues. In this study, we targeted the device-related issues by measuring sound localization performance of 11 NH listeners, listening to free-field stimuli processed by a real-time CI vocoder. The use of a real-time vocoder is a new approach, which enables testing in a free-field environment. For the NH listening condition, all listeners accurately and precisely localized sounds according to a linear stimulus–response relationship with an optimal gain and a minimal bias both in the azimuth and in the elevation directions. In contrast, when listening with bilateral real-time vocoders, listeners tended to orient either to the left or to the right in azimuth and were unable to determine sound source elevation. When listening with an NH ear and a unilateral vocoder, localization was impoverished on the vocoder side but improved toward the NH side. Localization performance was also reflected by systematic variations in reaction times across listening conditions. We conclude that perturbation of interaural temporal cues, reduction of interaural level cues, and removal of spectral pinna cues by the vocoder impairs sound localization. Listeners seem to ignore cues that were made unreliable by the vocoder, leading to acute reweighting of available localization cues. We discuss how current CI processors prevent CI users from localizing sounds in everyday environments.

The frequency-specific tone-evoked auditory brainstem response (ABR) is an indispensable tool in both the audiology clinic and research laboratory. Most frequently, the toneburst ABR is used to estimate hearing thresholds in infants, toddlers, and other patients for whom behavioral testing is not feasible. Therefore, results of the ABR exam form the basis for decisions regarding interventions and hearing habilitation with implications extending far into the child’s future. Currently, responses are elicited by periodic sequences of toneburst stimuli presented serially to one ear at a time, which take a long time to measure multiple frequencies and intensities, and provide incomplete information if the infant wakes up early. Here, we describe a new method, the parallel ABR (pABR), which uses randomly timed toneburst stimuli to simultaneously acquire ABR waveforms to five frequencies in both ears. Here, we describe the pABR and quantify its effectiveness in addressing the greatest drawback of current methods: test duration. We show that in adults with normal hearing the pABR yields high-quality waveforms over a range of intensities, with similar morphology to the standard ABR in a fraction of the recording time. Furthermore, longer latencies and smaller amplitudes for low frequencies at a high intensity evoked by the pABR versus serial ABR suggest that responses may have better place specificity due to the masking provided by the other simultaneous toneburst sequences. Thus, the pABR has substantial potential for facilitating faster accumulation of more diagnostic information that is important for timely identification and treatment of hearing loss.

Evaluation of patients who are unable to provide behavioral responses on standard clinical measures is challenging due to the lack of standard objective (non-behavioral) clinical audiological measures that assess the outcome of an intervention (e.g., hearing aids). Brainstem responses to short consonant-vowel stimuli (speech-auditory brainstem responses [speech-ABRs]) have been proposed as a measure of subcortical encoding of speech, speech detection, and speech-in-noise performance in individuals with normal hearing. Here, we investigated the potential application of speech-ABRs as an objective clinical outcome measure of speech detection, speech-in-noise detection and recognition, and self-reported speech understanding in 98 adults with sensorineural hearing loss. We compared aided and unaided speech-ABRs, and speech-ABRs in quiet and in noise. In addition, we evaluated whether speech-ABR F0 encoding (obtained from the complex cross-correlation with the 40 ms [da] fundamental waveform) predicted aided behavioral speech recognition in noise or aided self-reported speech understanding. Results showed that (a) aided speech-ABRs had earlier peak latencies, larger peak amplitudes, and larger F0 encoding amplitudes compared to unaided speech-ABRs; (b) the addition of background noise resulted in later F0 encoding latencies but did not have an effect on peak latencies and amplitudes or on F0 encoding amplitudes; and (c) speech-ABRs were not a significant predictor of any of the behavioral or self-report measures. These results show that speech-ABR F0 encoding is not a good predictor of speech-in-noise recognition or self-reported speech understanding with hearing aids. However, our results suggest that speech-ABRs may have potential for clinical application as an objective measure of speech detection with hearing aids.

The objective was to determine the effects of two frequency-lowering algorithms (frequency transposition, FT, and frequency compression, FC) on audibility, speech identification, and subjective benefit, for people with high-frequency hearing loss and extensive dead regions (DRs) in the cochlea. A single-blind randomized crossover design was used. FT and FC were compared with each other and with a control condition (denoted ‘Control’) without frequency lowering, using hearing aids that were otherwise identical. Data were collected after at least 6 weeks of experience with a condition. Outcome measures were audibility, scores for consonant identification, scores for word-final /s, z/ detection ( S test), sentence-in-noise intelligibility, and a questionnaire assessing self-perceived benefit (Spatial and Qualities of Hearing Scale). Ten adults with steeply sloping high-frequency hearing loss and extensive DRs were tested. FT and FC improved the audibility of some high-frequency sounds for 7 and 9 participants out of 10, respectively. At the group level, performance for FT and FC did not differ significantly from that for Control for any of the outcome measures. However, the pattern of consonant confusions varied across conditions. Bayesian analysis of the confusion matrices revealed a trend for FT to lead to more consistent error patterns than FC and Control. Thus, FT may have the potential to give greater benefit than Control or FC following extended experience or training.

Understanding cortical processing of spectrally degraded speech in normal-hearing subjects may provide insights into how sound information is processed by cochlear implant (CI) users. This study investigated electrocorticographic (ECoG) responses to noise-vocoded speech and related these responses to behavioral performance in a phonemic identification task. Subjects were neurosurgical patients undergoing chronic invasive monitoring for medically refractory epilepsy. Stimuli were utterances /aba/ and /ada/, spectrally degraded using a noise vocoder (1-4 bands). ECoG responses were obtained from Heschl's gyrus (HG) and superior temporal gyrus (STG), and were examined within the high gamma frequency range (70-150 Hz). All subjects performed at chance accuracy with speech degraded to 1 and 2 spectral bands, and at or near ceiling for clear speech. Inter-subject variability was observed in the 3- and 4-band conditions. High gamma responses in posteromedial HG (auditory core cortex) were similar for all vocoded conditions and clear speech. A progressive preference for clear speech emerged in anterolateral segments of HG, regardless of behavioral performance. On the lateral STG, responses to all vocoded stimuli were larger in subjects with better task performance. In contrast, both behavioral and neural responses to clear speech were comparable across subjects regardless of their ability to identify degraded stimuli. Findings highlight differences in representation of spectrally degraded speech across cortical areas and their relationship to perception. The results are in agreement with prior non-invasive results. The data provide insight into the neural mechanisms associated with variability in perception of degraded speech and potentially into sources of such variability in CI users.

The medial olivocochlear reflex (MOCR) has been implicated in several auditory processes. The putative role of the MOCR in improving speech perception in noise is particularly relevant for children who complain of listening difficulties (LiD). The hypothesis that the MOCR may be impaired in individuals with LiD or auditory processing disorder has led to several investigations but without consensus. In two related studies, we compared the MOCR functioning of children with LiD and typically developing (TD) children in the same age range (7–17 years). In Study 1, we investigated ipsilateral, contralateral, and bilateral MOCR using forward-masked click-evoked otoacoustic emissions (CEOAEs; n = 17 TD, 17 LiD). In Study 2, we employed three OAE types: CEOAEs ( n = 16 TD, 21 LiD), stimulus frequency OAEs ( n = 21 TD, 30 LiD), and distortion product OAEs ( n = 17 TD, 22 LiD) in a contralateral noise paradigm. Results from both studies suggest that the MOCR functioning is not significantly different between the two groups. Some likely reasons for differences in findings among published studies could stem from the lack of strict data quality measures (e.g., high signal-to-noise ratio, control for the middle ear muscle reflex) that were enforced in the present study. The inherent variability of the MOCR, the subpar reliability of current MOCR methods, and the heterogeneity in auditory processing deficits that underlie auditory processing disorder make detecting clinically relevant differences in MOCR function impractical using current methods.

Objectives: Masked speech recognition in normal-hearing listeners depends in part on masker type and semantic context of the target. Children and older adults are more susceptible to masking than young adults, particularly when the masker is speech. Semantic context has been shown to facilitate noise-masked sentence recognition in all age groups, but it is not known whether age affects a listener’s ability to use context with a speech masker. The purpose of the present study was to evaluate the effect of masker type and semantic context of the target as a function of listener age. Design: Listeners were children (5 to 16 years), young adults (19 to 30 years), and older adults (67 to 81 years), all with normal or near-normal hearing. Maskers were either speech-shaped noise or two-talker speech, and targets were either semantically correct (high context) sentences or semantically anomalous (low context) sentences. Results: As predicted, speech reception thresholds were lower for young adults than either children or older adults. Age effects were larger for the two-talker masker than the speech-shaped noise masker, and the effect of masker type was larger in children than older adults. Performance tended to be better for targets with high than low semantic context, but this benefit depended on age group and masker type. In contrast to adults, children benefitted less from context in the two-talker speech masker than the speech-shaped noise masker. Context effects were small compared with differences across age and masker type. Conclusions: Different effects of masker type and target context are observed at different points across the lifespan. While the two-talker masker is particularly challenging for children and older adults, the speech masker may limit the use of semantic context in children but not adults.

The article reports three experiments conducted to determine whether musicians possess better ability of recognising the sources of natural sounds than non-musicians. The study was inspired by reports which indicate that musical training develops not only musical hearing, but also enhances various non-musical auditory capabilities. Recognition and detection thresholds were measured for recordings of environmental sounds presented in quiet (Experiment 1) and in the background of a noise masker (Experiment 2). The listener’s ability of sound source recognition was inferred from the recognition-detection threshold gap (RDTG) defined as the difference in signal level between the thresholds of sound recognition and sound detection. Contrary to what was expected from reports of enhanced auditory abilities of musicians, the RDTGs were not smaller for musicians than for non-musicians. In Experiment 3, detection thresholds were measured with an adaptive procedure comprising three interleaved stimulus tracks with different sounds. It was found that the threshold elevation caused by stimulus interleaving was similar for musicians and non-musicians. The lack of superiority of musicians over non-musicians in the auditory tasks explored in this study is explained in terms of a listening strategy known as casual listening mode, which is a basis for auditory orientation in the environment.

Psychophysical methods similar to those employed with bats were used to examine jittered echo-delay resolution in bottlenose dolphins (Tursiops truncatus). Two dolphins were trained to produce echolocation clicks and report a change from electronic echoes with a fixed delay of ~ 12.6 ms (~ 9.4 m simulated range) to echoes with delays that alternated (jittered) between successive emitted signals. Jitter delays varied from 0 to 50 µs. Jittered echo-delay thresholds were between 1 and 2 µs-the lowest achievable (non-zero) values with the hardware configuration. Error functions matched the click autocorrelation function near zero jitter delay, and were well within the envelope of the autocorrelation function; however, measured jitter delay thresholds were larger than predictions for a coherent or semicoherent receiver at comparable signal-to-noise ratios. When one of the two alternating jittered echoes was inverted in polarity, both dolphins reliably discriminated echoes at all jittered echo delays, including 0 µs (i.e., only jittering in polarity, not delay). Finally, both dolphins used unusual patterns of click emissions, where groups of echolocation clicks were interspersed with silent gaps. Further tests with sub-microsecond jitter values and various echo signal-to-noise ratios would be necessary for proper direct comparison with jitter detection values obtained for bats.

How the human auditory system learns to map complex pinna-induced spectral-shape cues onto veridical estimates of sound-source elevation in the median plane is still unclear. Earlier studies demonstrated considerable sound-localisation plasticity after applying pinna moulds, and to altered vision. Several factors may contribute to auditory spatial learning, like visual or motor feedback, or updated priors. We here induced perceptual learning for sounds with degraded spectral content, having weak, but consistent, elevation-dependent cues, as demonstrated by low-gain stimulus-response relations. During training, we provided visual feedback for only six targets in the midsagittal plane, to which listeners gradually improved their response accuracy. Interestingly, listeners’ performance also improved without visual feedback, albeit less strongly. Post-training results showed generalised improved response behaviour, also to non-trained locations and acoustic spectra, presented throughout the two-dimensional frontal hemifield. We argue that the auditory system learns to reweigh contributions from low-informative spectral bands to update its prior elevation estimates, and explain our results with a neuro-computational model.

Objectives: The purpose of this study was to obtain an electrophysiological analog of masking release using speech-evoked cortical potentials in steady and modulated maskers and to relate this masking release to behavioral measures for the same stimuli. The hypothesis was that the evoked potentials can be tracked to a lower stimulus level in a modulated masker than in a steady masker and that the magnitude of this electrophysiological masking release is of the same order as that of the behavioral masking release for the same stimuli. Design: Cortical potentials evoked by an 80-ms /ba/ stimulus were measured in two steady maskers (30 and 65 dB SPL), and in a masker that modulated between these two levels at a rate of 25 Hz. In each masker, a level series was undertaken to determine electrophysiological threshold. Behavioral detection thresholds were determined in the same maskers using an adaptive tracking procedure. Masking release was defined as the difference between signal thresholds measured in the steady 65-dB SPL masker and the modulated masker. A total of 23 normal-hearing adults participated. Results: Electrophysiological thresholds were uniformly elevated relative to behavioral thresholds by about 6.5 dB. However, the magnitude of masking release was about 13.5 dB for both measurement domains. Conclusions: Electrophysiological measures of masking release using speech-evoked cortical auditory evoked potentials correspond closely to behavioral estimates for the same stimuli. This suggests that objective measures based on electrophysiological techniques can be used to reliably gauge aspects of temporal processing ability.