Measurement of Loudness, Part I: Methods, Problems, and Pitfalls

Biological relevance and methodological implications of unexpected hearing thresholds in a diving bird

Many animals alternate between different media, such as air and water, thanks to specific adaptations. Among birds, penguins (Sphenisciformes) have the most extreme morphological, physiological, and behavioural adaptations to their amphibious lifestyle. Their auditory perception of sound, potentially matching different impedances in air and under water, is largely unknown particularly in terms of whether their underwater adaptations may have affected their in-air hearing capacity. In this context, we investigated the hearing ability of four captive Humboldt penguins (Spheniscus humboldti) in air using psychophysical hearing tests. The 50% hit rate was found to be below 76 dB rms re 20 µPa between 0.250 kHz and 10 kHz, with most sensitive hearing at 2 kHz (mean threshold of 15.3 dB rms re 20 µPa). The four penguins showed large inter-individual variation in sensitivity at a given frequency but within a common audiogram shape. Despite the variability, penguins detected 0.250 kHz at comparably low sound levels (mean = 36.8 dB rms re 20 µPa) after a rapid decline of sensitivity at 0.500 kHz (mean = 64.1 dB rms re 20 µPa). This finding was unexpected, and it is therefore difficult to interpret whether it is an artefact of the methods or a biologically relevant finding. An extensive discussion is presented and suggests that this finding may be biologically relevant but would need further investigation to reveal the underlying mechanisms.

The CANDOR corpus: Insights from a large multimodal dataset of naturalistic conversation

People spend a substantial portion of their lives engaged in conversation, and yet, our scientific understanding of conversation is still in its infancy. Here, we introduce a large, novel, and multimodal corpus of 1656 conversations recorded in spoken English. This 7+ million word, 850-hour corpus totals more than 1 terabyte of audio, video, and transcripts, with moment-to-moment measures of vocal, facial, and semantic expression, together with an extensive survey of speakers' postconversation reflections. By taking advantage of the considerable scope of the corpus, we explore many examples of how this large-scale public dataset may catalyze future research, particularly across disciplinary boundaries, as scholars from a variety of fields appear increasingly interested in the study of conversation.

Evaluation of Remote Categorical Loudness Scaling

PURPOSE

The aims of this study were to (a) demonstrate the feasibility of administering categorical loudness scaling (CLS) tests in a remote setting, (b) assess the reliability of remote compared with laboratory CLS results, and (c) provide preliminary evidence of the validity of remote CLS testing.

METHOD

CLS data from 21 adult participants collected in a home setting were compared to CLS data collected in a laboratory setting from previous studies. Five participants took part in studies in both settings. Precalibrated equipment was delivered to participants who performed headphone output level checks and measured ambient noise levels. After a practice run, CLS measurements were collected for two runs at 1 and 4 kHz.

RESULTS

Mean headphone output levels were within 1.5 dB of the target calibration level. Mean ambient noise levels were below the target level. Within-run variability was similar between the two settings, but across-run bias was smaller for data collected in the laboratory setting compared with the remote setting. Systematic differences in CLS functions were not observed for the five individuals who participated in both settings.

CONCLUSIONS

This study demonstrated that precise stimulus levels can be delivered and background noise levels can be controlled in a home environment. Across-run bias for remote CLS was larger than for in-laboratory CLS, indicating that further work is needed to improve the reliability of CLS data collected in remote settings. Supplemental Material https://doi.org/10.23641/asha.17131856.

The Perception of Ramped Pulse Shapes in Cochlear Implant Users

The electric stimulation provided by current cochlear implants (CI) is not power efficient. One underlying problem is the poor efficiency by which information from electric pulses is transformed into auditory nerve responses. A novel stimulation paradigm using ramped pulse shapes has recently been proposed to remedy this inefficiency. The primary motivation is a better biophysical fit to spiral ganglion neurons with ramped pulses compared to the rectangular pulses used in most contemporary CIs. Here, we tested the hypotheses that ramped pulses provide more efficient stimulation compared to rectangular pulses and that a rising ramp is more efficient than a declining ramp. Rectangular, rising ramped and declining ramped pulse shapes were compared in terms of charge efficiency and discriminability, and threshold variability in seven CI listeners. The tasks included single-channel threshold detection, loudness-balancing, discrimination of pulse shapes, and threshold measurement across the electrode array. Results showed that reduced charge, but increased peak current amplitudes, was required at threshold and most comfortable levels with ramped pulses relative to rectangular pulses. Furthermore, only one subject could reliably discriminate between equally-loud ramped and rectangular pulses, suggesting variations in neural activation patterns between pulse shapes in that participant. No significant difference was found between rising and declining ramped pulses across all tests. In summary, the present findings show some benefits of charge efficiency with ramped pulses relative to rectangular pulses, that the direction of a ramped slope is of less importance, and that most participants could not perceive a difference between pulse shapes.

Functional neuroimaging in hearing research and audiology

The various methods of medical imaging are essential for many diagnostic issues in clinical routine, e.g., for the diagnostics and localisation of tumorous diseases, or for the clarification of other lesions in the central nervous system. In addition to these classical roles both positron emission tomography (PET) and magnetic resonance imaging (MRI) allow for the investigation of functional processes in the human brain, when used in a specific way. The last 25 years have seen great progress, especially with respect to functional MRI, in terms of the available experimental paradigms as well as the data analysis strategies, so that a directed investigation of neurophysiological correlates of psychoacoustic performance is possible. This covers fundamental measures of sound perception like loudness and pitch, specific audiological symptoms like tinnitus, which often accompanies hearing disorders, but it also includes experiments on speech perception or on virtual acoustic environments. One important aspect common to many auditory neuroimaging studies is the central question at what stage in the human auditory pathway the sensory coding of the incoming sound is transformed into a universal and context-dependent perceptual representation, which is the basis for what we hear. This overview summarises findings from the literature as well as a few studies from our lab, to discuss the possibilities and the limits of the adoption of functional neuroimaging methods in audiology. Up to this stage, most auditory neuroimaging studies have investigated basic processes in normal hearing listeners. However, the hitherto existing results suggest that the methods of auditory functional neuroimaging - possibly complemented by electrophysiological methods like EEG and MEG - have a great potential to contribute to a deeper understanding of the processes and the impact of hearing disorders.

A psychoacoustic test for diagnosing hyperacusis based on ratings of natural sounds

Hyperacusis is defined as an increased sensitivity to sounds, i.e. sounds presented at moderate levels can produce discomfort or even pain. Existing diagnostic methods, like the Hyperacusis Questionnaire (HQ) and Loudness Discomfort Levels (LDLs), have been challenged because of their variability and lack of agreement on appropriate cut-off values. We propose a novel approach by using psychoacoustic ratings of natural sounds as an assessment tool for hyperacusis. Subjects (n = 81) were presented with natural and artificial (tone pips, noises) sounds (n = 69) in a controlled environment at four sound levels (60, 70, 80 and 90 dB SPL). The task was to rate them on a pleasant to unpleasant visual analog scale. The inherent challenge of this study was to create a new diagnostic tool when no gold standard of hyperacusis diagnosis exists. We labeled our subjects as hyperacusic (n = 26) when they were diagnosed as such by at least two of three methods (HQ, LDLs and self-report). There was a significant difference between controls (n = 23) and hyperacusics in the median global rating of pleasant sounds. Median global ratings of unpleasant sounds and artificial sounds did not differ significantly. Then we selected the subset of sounds that could best discriminate the controls from the hyperacusics, the Core Discriminant Sounds (CDS), and we used them to develop a new metric: The CDS score. A normalized global score and a score for each sound level can be computed with respect to a control population without hyperacusis. A receiver operating characteristic analysis showed that the accuracy of our method in distinguishing subjects with and without complaints of hyperacusis (86%, 95% Confidence Interval (CI): 76-93%) is comparable to that of existing methods such as the LDL (77%, CI: 67-86%) and the HQ (80%, CI: 69-88%). We believe that the CDS score is more relevant to subject's complaints than LDLs and that it could be applied in a clinical environment in a fast and effective way, while minimizing discomfort and biases.

Objective Binaural Loudness Balancing Based on 40-Hz Auditory Steady-State Responses. Part I: Normal Hearing

Psychophysical procedures are used to balance loudness across the ears. However, they can be difficult and require active cooperation. We investigated whether 40-Hz auditory steady-state response (ASSR) amplitudes can be used to objectively estimate the balanced loudness across the ears for a group of young, normal-hearing participants. The 40-Hz ASSRs were recorded using monaural stimuli with carrier frequencies of 500, 1000, or 2000 Hz over a range of levels between 40 and 80 dB SPL. Behavioral loudness balancing was performed for at least one reference level of the left ear. ASSR amplitude growth functions were listener dependent, but median across-ear ratios in ASSR amplitudes were close to 1. The differences between the ASSR-predicted balanced levels and the behaviorally found balanced levels were smaller than 5 dB in 59% of cases and smaller than 10 dB in 85% of cases. The differences between the ASSR-predicted balanced levels and the reference levels were smaller than 5 dB in 54% of cases and smaller than 10 dB in 87% of cases. No clear hemispheric lateralization was found for 40-Hz ASSRs, with the exception of responses evoked by stimulus levels of 40 to 60 dB SPL at 2000 Hz.

Objective Binaural Loudness Balancing Based on 40-Hz Auditory Steady-State Responses. Part II: Asymmetric and Bimodal Hearing

In Part I, we investigated 40-Hz auditory steady-state response (ASSR) amplitudes for the use of objective loudness balancing across the ears for normal-hearing participants and found median across-ear ratios in ASSR amplitudes close to 1. In this part, we further investigated whether the ASSR can be used to estimate binaural loudness balance for listeners with asymmetric hearing, for whom binaural loudness balancing is of particular interest. We tested participants with asymmetric hearing and participants with bimodal hearing, who hear with electrical stimulation through a cochlear implant (CI) in one ear and with acoustical stimulation in the other ear. Behavioral loudness balancing was performed at different percentages of the dynamic range. Acoustical carrier frequencies were 500, 1000, or 2000 Hz, and CI channels were stimulated in apical or middle regions in the cochlea. For both groups, the ASSR amplitudes at balanced loudness levels were similar for the two ears, with median ratios between left and right ear stimulation close to 1. However, individual variability was observed. For participants with asymmetric hearing loss, the difference between the behavioral balanced levels and the ASSR-predicted balanced levels was smaller than 10 dB in 50% and 56% of cases, for 500 Hz and 2000 Hz, respectively. For bimodal listeners, these percentages were 89% and 60%. Apical CI channels yielded significantly better results (median difference near 0 dB) than middle CI channels, which had a median difference of −7.25 dB.

Feasibility of interleaved Bayesian adaptive procedures in estimating the equal-loudness contour

A Bayesian adaptive procedure, the interleaved-equal-loudness contour (IELC) procedure, was developed to improve the efficiency in estimating the equal-loudness contour. Experiment 1 evaluated the test-retest reliability of the IELC procedure using six naive normal-hearing listeners. Two IELC runs of 200 trials were conducted and excellent test-retest reliability was found at both the group and individual levels. Using the same group of listeners, Experiment 2 compared the IELC procedure to two other procedures that required frequency-by-frequency testing. One of these procedures was the commonly adopted interleaved staircase (ISC) procedure from Jesteadt [(1980). Atten. Percept. Psychophys. 28, 85-88]. The other procedure, the interleaved maximum-likelihood (IML) procedure, was a modification of the updated maximum-likelihood procedure [Shen and Richards (2012). J. Acoust. Soc. Am. 132, 957-967]. For each of the ISC and IML procedures, two runs of approximately 500 trials were conducted, followed by one additional IELC run. The test-retest reliability of the IELC procedure was comparable to that of the ISC and IML procedure. The accuracies of all three procedures measured in Experiment 2 were similar, which was superior to the accuracies of the IELC runs from Experiment 1, indicating a potential training effect.

Influence of suppression on restoration of spectral loudness summation in listeners with hearing loss

Loudness depends on both the intensity and spectrum of a sound. Listeners with normal hearing perceive a broadband sound as being louder than an equal-level narrowband sound because loudness grows nonlinearly with level and is then summed across frequency bands. This difference in loudness as a function of bandwidth is reduced in listeners with sensorineural hearing loss (SNHL). Suppression, the reduction in the cochlear response to one sound by the simultaneous presentation of another sound, is also reduced in listeners with SNHL. Hearing-aid gain that is based on loudness measurements with pure tones may fail to restore normal loudness growth for broadband sounds. This study investigated whether hearing-aid amplification that mimics suppression can improve loudness summation for listeners with SNHL. Estimates of loudness summation were obtained using measurements of categorical loudness scaling (CLS). Stimuli were bandpass-filtered noises centered at 2 kHz with bandwidths in the range of 0.1-6.4 kHz. Gain was selected to restore normal loudness based on CLS measurements with pure tones. Gain that accounts for both compression and suppression resulted in better restoration of loudness summation, compared to compression alone. However, restoration was imperfect, suggesting that additional refinements to the signal processing and gain-prescription algorithms are needed.

Deriving loudness growth functions from categorical loudness scaling data

The goal of this study was to reconcile the differences between measures of loudness obtained with continuous, unbounded scaling procedures, such as magnitude estimation and production, and those obtained using a limited number of discrete categories, such as categorical loudness scaling (CLS). The former procedures yield data with ratio properties, but some listeners find it difficult to generate numbers proportional to loudness and the numbers cannot be compared across listeners to explore individual differences. CLS, where listeners rate loudness on a verbal scale, is an easier task, but the numerical values or categorical units (CUs) assigned to the points on the scale are not proportional to loudness. Sufficient CLS data are now available to assign values in sones, a scale proportional to loudness, to the loudness categories. As a demonstration of this approach, data from Heeren, Hohmann, Appell, and Verhey [J. Acoust. Soc. Am. 133, EL314-EL319 (2013)] were used to develop a CUsone metric, whose values were then substituted for the original CU values in reanalysis of a large set of CLS data obtained by Rasetshwane, Trevino, Gombert, Liebig-Trehearn, Kopun, Jesteadt, Neely, and Gorga [J. Acoust. Soc. Am. 137, 1899-1913 (2015)]. The resulting data are well fitted by power functions and are in general agreement with previously published results obtained with magnitude estimation, magnitude production, and cross modality matching.

Inconsistent Effect of Arousal on Early Auditory Perception

Mood has been shown to influence cognitive performance. However, little is known about the influence of mood on sensory processing, specifically in the auditory domain. With the current study, we sought to investigate how auditory processing of neutral sounds is affected by the mood state of the listener. This was tested in two experiments by measuring masked-auditory detection thresholds before and after a standard mood-induction procedure. In the first experiment (N = 76), mood was induced by imagining a mood-appropriate event combined with listening to mood inducing music. In the second experiment (N = 80), imagining was combined with affective picture viewing to exclude any possibility of confounding the results by acoustic properties of the music. In both experiments, the thresholds were determined by means of an adaptive staircase tracking method in a two-interval forced-choice task. Masked detection thresholds were compared between participants in four different moods (calm, happy, sad, and anxious), which enabled differentiation of mood effects along the dimensions arousal and pleasure. Results of the two experiments were analyzed both in separate analyses and in a combined analysis. The first experiment showed that, while there was no impact of pleasure level on the masked threshold, lower arousal was associated with lower threshold (higher masked sensitivity). However, as indicated by an interaction effect between experiment and arousal, arousal did have a different effect on the threshold in Experiment 2. Experiment 2 showed a trend of arousal in opposite direction. These results show that the effect of arousal on auditory-masked sensitivity may depend on the modality of the mood-inducing stimuli. As clear conclusions regarding the genuineness of the arousal effect on the masked threshold cannot be drawn, suggestions for further research that could clarify this issue are provided.

Development of a multi-category psychometric function to model categorical loudness measurements

A multi-category psychometric function (MCPF) is introduced for modeling the stimulus-level dependence of perceptual categorical probability distributions. The MCPF is described in the context of individual-listener categorical loudness scaling (CLS) data. During a CLS task, listeners select the loudness category that best corresponds to their perception of the presented stimulus. In this study, CLS MCPF results are reported for 37 listeners (15 normal hearing, 22 with hearing loss). Individual-listener MCPFs were parameterized, and a principal component analysis (PCA) was used to identify sources of inter-subject variability and reduce the dimensionality of the data. A representative "catalog" of potential listener MCPFs was created from the PCA results. A method is introduced for using the MCPF catalog and maximum-likelihood estimation, together, to derive CLS functions for additional participants; this technique improved the accuracy of the CLS results and provided a MCPF model for each listener. Such a technique is particularly beneficial when a relatively low number of measurements are available (e.g., International Standards Organization adaptive-level CLS testing). In general, the MCPF is a flexible tool that can characterize any type of ordinal, level-dependent categorical data. For CLS, the MCPF quantifies the suprathreshold variability across listeners and provides a model for probability-based analyses and methods.

The representation of level and loudness in the central auditory system for unilateral stimulation

Loudness is the perceptual correlate of the physical intensity of a sound. However, loudness judgments depend on a variety of other variables and can vary considerably between individual listeners. While functional magnetic resonance imaging (fMRI) has been extensively used to characterize the neural representation of physical sound intensity in the human auditory system, only few studies have also investigated brain activity in relation to individual loudness. The physiological correlate of loudness perception is not yet fully understood. The present study systematically explored the interrelation of sound pressure level, ear of entry, individual loudness judgments, and fMRI activation along different stages of the central auditory system and across hemispheres for a group of normal hearing listeners. 4-kHz-bandpass filtered noise stimuli were presented monaurally to each ear at levels from 37 to 97dB SPL. One diotic condition and a silence condition were included as control conditions. The participants completed a categorical loudness scaling procedure with similar stimuli before auditory fMRI was performed. The relationship between brain activity, as inferred from blood oxygenation level dependent (BOLD) contrasts, and both sound level and loudness estimates were analyzed by means of functional activation maps and linear mixed effects models for various anatomically defined regions of interest in the ascending auditory pathway and in the cortex. Our findings are overall in line with the notion that fMRI activation in several regions within auditory cortex as well as in certain stages of the ascending auditory pathway might be more a direct linear reflection of perceived loudness rather than of sound pressure level. The results indicate distinct functional differences between midbrain and cortical areas as well as between specific regions within auditory cortex, suggesting a systematic hierarchy in terms of lateralization and the representation of level and loudness.¹.

Underwater Equal-Latency Contours of a Harbor Porpoise (Phocoena phocoena) for Tonal Signals Between 0.5 and 125 kHz

Loudness perception can be studied based on the assumption that sounds of equal loudness elicit equal reaction time (RT; or "response latency"). We measured the underwater RTs of a harbor porpoise to narrowband frequency-modulated sounds and constructed six equal-latency contours. The contours paralleled the audiogram at low sensation levels (high RTs). At high-sensation levels, contours flattened between 0.5 and 31.5 kHz but dropped substantially (RTs shortened) beyond those frequencies. This study suggests that equal-latency-based frequency weighting can emulate noise perception in porpoises for low and middle frequencies but that the RT-loudness correlation is relatively weak for very high frequencies.

Categorical loudness scaling and equal-loudness contours in listeners with normal hearing and hearing loss

This study describes procedures for constructing equal-loudness contours (ELCs) in units of phons from categorical loudness scaling (CLS) data and characterizes the impact of hearing loss on these estimates of loudness. Additionally, this study developed a metric, level-dependent loudness loss, which uses CLS data to specify the deviation from normal loudness perception at various loudness levels and as function of frequency for an individual listener with hearing loss. CLS measurements were made in 87 participants with hearing loss and 61 participants with normal hearing. An assessment of the reliability of CLS measurements was conducted on a subset of the data. CLS measurements were reliable. There was a systematic increase in the slope of the low-level segment of the CLS functions with increase in the degree of hearing loss. ELCs derived from CLS measurements were similar to standardized ELCs (International Organization for Standardization, ISO 226:2003). The presence of hearing loss decreased the vertical spacing of the ELCs, reflecting loudness recruitment and reduced cochlear compression. Representing CLS data in phons may lead to wider acceptance of CLS measurements. Like the audiogram that specifies hearing loss at threshold, level-dependent loudness loss describes deficit for suprathreshold sounds. Such information may have implications for the fitting of hearing aids.

Spectral loudness summation: shortcomings of current standards

There are two competing national standards for the calculation of loudness of steady sounds, DIN 45631 and ANSI S3.4. Their different concepts of critical bands lead to different predictions for broadband sounds. As that discrepancy is neither constant nor linear but highly frequency-dependent, the present study investigates spectral loudness summation in three frequency regions, at various levels, and using two different methods. The results show that both algorithms overestimate loudness; however, DIN 45631 comes closer to the subjective evaluations and often falls within their interquartile range. The overestimation by the standards is particularly large in the frequency range from 2 to 5 kHz.

Representation of loudness in the auditory cortex

Changes in stimulus intensity are reflected in changes in the fundamental perceptual attribute of loudness. Stimulus intensity changes also profoundly impact the evoked neural responses throughout the auditory system. A fundamental question is how measurements of neural activity, from the single-neuron level to mass-activity metrics such as functional magnetic resonance imaging or magnetoencephalography, reflect the physical properties of stimulus intensity as opposed to perceived loudness. In this chapter we discuss findings from psychophysics and animal neurophysiology as well as human brain activity measurements to clarify our current understanding of the neural mechanisms that contribute to the perceptual correlate of stimulus intensity.

Binaural loudness gain measured by simple reaction time

In order to yield equal loudness, different studies using scaling or matching methods have found binaural level differences between monaural and diotic presentations ranging from less than 2 dB to as much as 10 dB. In the present study, a reaction time methodology was employed to measure the binaural level difference producing equal reaction time (BLDERT). Participants had to respond to the onset of 1-kHz pure tones with sound pressure levels ranging from 45 to 85 dB, and being presented to the right, the left, or both ears. Equal RTs for monaural and diotic presentation (BLDERTs) were obtained with a level difference of approximately 5 dB. A second experiment showed that different results obtained for the left and right ear are largely due to the responding hand, with ipsilateral responses being faster than contralateral ones. A third experiment investigated the BLDERT for dichotic stimuli, tracing the transition between binaural and monaural stimulation. The results of all three RT experiments are consistent with current models of binaural loudness and contradict earlier claims of perfect binaural summation.

Equal latency contours and auditory weighting functions for the harbour porpoise (Phocoena phocoena)

Loudness perception by human infants and animals can be studied under the assumption that sounds of equal loudness elicit equal reaction times (RTs). Simple RTs of a harbour porpoise to narrowband frequency-modulated signals were measured using a behavioural method and an RT sensor based on infrared light. Equal latency contours, which connect equal RTs across frequencies, for reference values of 150-200 ms (10 ms intervals) were derived from median RTs to 1 s signals with sound pressure levels (SPLs) of 59-168 dB re. 1 μPa and centre frequencies of 0.5, 1, 2, 4, 16, 31.5, 63, 80 and 125 kHz. The higher the signal level was above the hearing threshold of the harbour porpoise, the quicker the animal responded to the stimulus (median RT 98-522 ms). Equal latency contours roughly paralleled the hearing threshold at relatively low sensation levels (higher RTs). The difference in shape between the hearing threshold and the equal latency contours was more pronounced at higher levels (lower RTs); a flattening of the contours occurred for frequencies below 63 kHz. Relationships of the equal latency contour levels with the hearing threshold were used to create smoothed functions assumed to be representative of equal loudness contours. Auditory weighting functions were derived from these smoothed functions that may be used to predict perceived levels and correlated noise effects in the harbour porpoise, at least until actual equal loudness contours become available.

Effects of expectations on loudness and loudness difference

To determine how expectations affect loudness and loudness difference, in two experiments we induced some subjects to expect loud sounds (condition L), some to expect soft sounds (condition S), and others to have no particular expectations (control). In Experiment 1, all subjects estimated the loudnesses of the same set of three moderately loud 1-kHz tones. Estimates were greatest for subjects in condition S and smallest for subjects in condition L. Control subjects' estimates were intermediate but closer to those of condition S subjects. In Experiment 2, subjects estimated the difference in loudness for pairs of moderately loud 1-kHz tones. Again, estimates were smallest for condition L subjects; estimates were greatest for control subjects, and condition S subjects' estimates were closer to control estimates than to condition L estimates. This pattern of results is explainable by a combination of (1) Parducci's (1995) range-frequency theory and (2) a gain control mechanism in the auditory system under top-down governance (Schneider, Parker, & Murphy, 2011).