Contribution of frequency bands to the loudness of broadband sounds: Tonal and noise stimuli.

Contributions of individual frequency bands to judgments of total loudness can be assessed by varying the level of each band independently from one presentation to the next and determining the relation between the change in level of each band and the loudness judgment. In a previous study, measures of perceptual weight obtained in this way for noise stimuli consisting of 15 bands showed greater weight associated with the highest and lowest bands than loudness models would predict. This was true even for noise with the long-term average speech spectrum, where the highest band contained little energy. One explanation is that listeners were basing decisions on some attribute other than loudness. The current study replicated earlier results for noise stimuli and included conditions using 15 tones located at the center frequencies of the noise bands. Although the two types of stimuli sound very different, the patterns of perceptual weight were nearly identical, suggesting that both sets of results are based on loudness judgments and that the edge bands play an important role in those judgments. The importance of the highest band was confirmed in a loudness-matching task involving all combinations of noise and tonal stimuli.

Effects of Amplification and Hearing Aid Experience on the Contribution of Specific Frequency Bands to Loudness.

OBJECTIVES: The primary aim of this study is to describe the effect of hearing aid amplification on the contribution of specific frequency bands to overall loudness in adult listeners with sensorineural hearing loss (SNHL). Results for listeners with SNHL were compared with results for listeners with normal hearing (NH) to evaluate whether amplification restores the normal perception of loudness for broadband sound. A secondary aim of this study is to determine whether the loudness perception of new hearing aid users becomes closer to normal over the first few months of hearing aid use. It was hypothesized that amplification would cause the high-frequency bands to contribute most to the perception of loudness and that this effect might decrease as new hearing aid users adapt to amplification. DESIGN: In experiment 1, 8 adult listeners with SNHL completed a two-interval forced-choice loudness task in unaided and aided conditions. A control group of 7 listeners with NH completed the task in the unaided condition only. Stimuli were composed of seven summed noise bands whose levels were independently adjusted between presentations. During a trial, two stimuli were presented, and listeners determined the louder one. The correlation between the difference in levels for a given noise band on every trial and the listener's response was calculated. The resulting measure is termed the perceptual weight because it provides an estimate of the relative contribution of a given frequency region to overall loudness. In experiment 2, a separate group of 6 new hearing aid users repeated identical procedures on 2 sessions separated by 12 weeks. RESULTS: Results for listeners with SNHL were similar in experiments 1 and 2. In the unaided condition, perceptual weights were greatest for the low-frequency bands. In the aided condition, perceptual weights were greatest for the high-frequency bands. On average, the aided perceptual weights for listeners with SNHL for high-frequency bands were greater than the unaided weights for listeners with NH. In experiment 2, hearing aid experience did not have a significant effect on perceptual weights. CONCLUSIONS: The high frequencies seem to dominate loudness perception in listeners with SNHL using hearing aids as they do in listeners with NH. However, the results suggest that amplification causes high frequencies to have a larger contribution to overall loudness compared with listeners with NH. The contribution of the high frequencies to loudness did not change after an acclimatization period for the first-time hearing aid users.

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.

The Influence of Hearing Aid Gain on Gap-Detection Thresholds for Children and Adults With Hearing Loss.

OBJECTIVES: The objective of this experiment was to examine the contributions of audibility to the ability to perceive a gap in noise for children and adults. Sensorineural hearing loss (SNHL) in adulthood is associated with a deficit in gap detection. It is well known that reduced audibility in adult listeners with SNHL contributes to this deficit; however, it is unclear the extent to which hearing aid amplification can restore gap-detection thresholds, and the effect of childhood SNHL on gap-detection thresholds have not been described. For adults, it was hypothesized that restoring the dynamic range of hearing for listeners with SNHL would lead to approximately normal gap-detection thresholds. Children with normal hearing (NH) exhibit poorer gap-detection thresholds than adults. Because of their hearing loss, children with SNHL have less auditory experience than their peers with NH. Yet, it is unknown the extent to which auditory experience impacts their ability to perceive gaps in noise. Even with the provision of amplification, it was hypothesized that children with SNHL would show a deficit in gap detection, relative to their peers with normal hearing, because of reduced auditory experience. DESIGN: The ability to detect a silent interval in noise was tested by adapting the stimulus level required for detection of gap durations between 3 and 20 ms for adults and children with and without SNHL. Stimulus-level thresholds were measured for participants with SNHL without amplification and with two prescriptive procedures-the adult and child versions of the desired sensation level i/o program-using a hearing aid simulator. The child version better restored the normal dynamic range than the adult version. Adults and children with NH were tested without amplification. RESULTS: When fitted using the procedure that best restored the dynamic range, adults with SNHL had stimulus-level thresholds similar to those of adults with normal hearing. Compared to the children with NH, the children with SNHL required a higher stimulus level to detect a 5-ms gap, despite having used the procedure that better restored the normal dynamic range of hearing. Otherwise, the two groups of children had similar stimulus-level thresholds. CONCLUSION: These findings suggest that apparent deficits in temporal resolution, as measured using stimulus-level thresholds for the detection of gaps, are dependent on age and audibility. These novel results indicate that childhood SNHL may impair temporal resolution as measured by stimulus-level thresholds for the detection of a gap in noise. This work has implications for understanding the effects of amplification on the ability to perceive temporal cues in speech.

Relative contributions of specific frequency bands to the loudness of broadband sounds.

Listeners with normal hearing (NH) and sensorineural hearing loss (SNHL) were asked to compare pairs of noise stimuli and choose the louder noise in each pair. Each noise was made up of 15, two-ERBN (equivalent rectangular bandwidth) wide frequency bands that varied independently over a 12-dB range from one presentation to the next. Mean levels of the bands followed the long-term average speech spectrum (LTASS) or were set to 43, 51, or 59 dB sound pressure level (SPL). The relative contribution of each band to the total loudness of the noise was determined by computing the correlation between the difference in levels for a given band on every trial and the listener's decision on that trial. Weights for SNHL listeners were governed by audibility and the spectrum of the noise stimuli, with bands near the spectral peak of the LTASS noise receiving greatest weight. NH listeners assigned greater weight to the lowest and highest bands, an effect that increased with overall level, but did not assign greater weight to bands near the LTASS peak. Additional loudness-matching and paired-comparison studies using stimuli missing one of the 15 bands showed a significant contribution by the highest band, but properties other than loudness may have contributed to the decisions.

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.

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.

Multi-tone suppression of distortion-product otoacoustic emissions in humans.

The purpose of this study was to investigate the combined effect of multiple suppressors. Distortion-product otoacoustic emission (DPOAE) measurements were made in normal-hearing participants. Primary tones had fixed frequencies (f2 = 4000 Hz; f1 / f2 = 1.22) and a range of levels. Suppressor tones were at three frequencies (fs = 2828, 4100, 4300 Hz) and range of levels. Decrement was defined as the attenuation in DPOAE level due to the presence of a suppressor. A measure of suppression called suppressive intensity was calculated by an equation previously shown to fit DPOAE suppression data. Suppressor pairs, which were the combination of two different frequencies, were presented at levels selected to have equal single-suppressor decrements. A hybrid model that represents a continuum between additive intensity and additive attenuation best described the results. The suppressor pair with the smallest frequency ratio produced decrements that were more consistent with additive intensity. The suppressor pair with the largest frequency ratio produced decrements at the highest level that were consistent with additive attenuation. Other suppressor-pair conditions produced decrements that were intermediate between these two alternative models. The hybrid model provides a useful framework for representing the observed range of interaction when two suppressors are combined.

Modeling the Individual Variability of Loudness Perception with a Multi-Category Psychometric Function.

Loudness is a suprathreshold percept that provides insight into the status of the entire auditory pathway. Individuals with matched thresholds can show individual variability in their loudness perception that is currently not well understood. As a means to analyze and model listener variability, we introduce the multi-category psychometric function (MCPF), a novel representation for categorical data that fully describes the probabilistic relationship between stimulus level and categorical-loudness perception. We present results based on categorical loudness scaling (CLS) data for adults with normal-hearing (NH) and hearing loss (HL). We show how the MCPF can be used to improve CLS estimates, by combining listener models with maximum-likelihood (ML) estimation. We also describe how the MCPF could be used in an entropy-based stimulus-selection technique. These techniques utilize the probabilistic nature of categorical perception, a novel usage of this dimension of loudness information, to improve the quality of loudness measurements.

Effects of relative and absolute frequency in the spectral weighting of loudness.

The loudness of broadband sound is often modeled as a linear sum of specific loudness across frequency bands. In contrast, recent studies using molecular psychophysical methods suggest that low and high frequency components contribute more to the overall loudness than mid frequencies. In a series of experiments, the contribution of individual components to the overall loudness of a tone complex was assessed using the molecular psychophysical method as well as a loudness matching task. The stimuli were two spectrally overlapping ten-tone complexes with two equivalent rectangular bandwidth spacing between the tones, making it possible to separate effects of relative and absolute frequency. The lowest frequency components of the "low-frequency" and the "high-frequency" complexes were 208 and 808 Hz, respectively. Perceptual-weights data showed emphasis on lowest and highest frequencies of both the complexes, suggesting spectral-edge related effects. Loudness matching data in the same listeners confirmed the greater contribution of low and high frequency components to the overall loudness of the ten-tone complexes. Masked detection thresholds of the individual components within the tone complex were not correlated with perceptual weights. The results show that perceptual weights provide reliable behavioral correlates of relative contributions of the individual frequency components to overall loudness of broadband sounds.

The influence of hearing-aid compression on forward-masked thresholds for adults with hearing loss.

This paper describes forward-masked thresholds for adults with hearing loss. Previous research has demonstrated that the loss of cochlear compression contributes to deficits in this measure of temporal resolution. Cochlear compression can be mimicked with fast-acting compression where the normal dynamic range is mapped to the impaired dynamic range. To test the hypothesis that fast-acting compression will most-closely approximate the normal ability to perceive forward-masked pure-tones, forward-masked thresholds were measured for two groups of adults (normal hearing, hearing loss). Adults with normal hearing were tested without amplification. Adults with hearing loss were tested with three different compression speeds and two different prescriptive procedures using a hearing-aid simulator. The two prescriptive procedures differed in the extent to which the normal dynamic range was mapped onto the impaired dynamic range. When using a faster compression speed with the prescriptive procedure that best restored the lost dynamic range, forward-masked thresholds for the listeners with hearing loss approximated those observed for the listeners with normal hearing.

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.

Perceptual weights for loudness judgments of six-tone complexes.

Subjects with normal hearing (NH) and with sensorineural hearing loss (SNHL) judged the overall loudness of six-tone complexes comprised of octave frequencies from 0.25 to 8 kHz. The level of each tone was selected from a normal distribution with a standard deviation of 5 dB, and subjects judged which of two complexes was louder. Overall level varied across conditions. In the "loudness" task, there was no difference in mean level across the two stimuli. In the "sample discrimination" task, the two complexes differed by an average of 5 dB. For both tasks, perceptual weights were derived by correlating the differences in level between matched-frequency tones in the complexes and the loudness decision on each trial. Weights obtained in the two tasks showed similar shifts from low to high frequency components with increasing overall level. Simulation of these experiments using a model of loudness perception [Moore and Glasberg (2004), Hear Res. 188, 70-88] yielded predicted weights for these stimuli that were highly correlated with predicted specific loudness, but not with the observed weights.

Factors limiting performance in a multitone intensity-discrimination task: disentangling non-optimal decision weights and increased internal noise.

To identify factors limiting performance in multitone intensity discrimination, we presented sequences of five pure tones alternating in level between loud (85 dB SPL) and soft (30, 55, or 80 dB SPL). In the "overall-intensity task", listeners detected a level increment on all of the five tones. In the "masking task", the level increment was imposed only on the soft tones, rendering the soft tones targets and loud tones task-irrelevant maskers. Decision weights quantifying the importance of the five tone levels for the decision were estimated using methods of molecular psychophysics. Compatible with previous studies, listeners placed higher weights on the loud tones than on the soft tones in the overall-intensity condition. In the masking task, the decisions were systematically influenced by the to-be-ignored loud tones (maskers). Using a maximum-likelihood technique, we estimated the internal noise variance and tested whether the internal noise was higher in the alternating-level five-tone sequences than in sequences presenting only the soft or only the loud tones. For the overall-intensity task, we found no evidence for increased internal noise, but listeners applied suboptimal decision weights. These results are compatible with the hypothesis that the presence of the loud tones does not impair the precision of the representation of the intensity of the soft tones available at the decision stage, but that this information is not used in an optimal fashion due to a difficulty in attending to the soft tones. For the masking task, in some cases our data indicated an increase in internal noise. Additionally, listeners applied suboptimal decision weights. The maximum-likelihood analyses we developed should also be useful for other tasks or other sensory modalities.

Nonadditivity of forward and simultaneous masking.

The current study measured the additional masking obtained for combinations of forward and simultaneous maskers as a function of forward masker bandwidth, signal delay, and simultaneous masker level. The effects of the two individual maskers were equated in all conditions. Additional masking increased with increasing masker level, increasing signal delay, and decreasing masker bandwidth. The portion of the simultaneous masker that made the greater contribution to additional masking was the part that overlapped with the signal, not with the forward masker. The changes in additional masking observed as a function of forward masker bandwidth and the interaction between the effects of forward and simultaneous maskers call into question the use of additional masking as a measure of basilar membrane compression and present problems for the use of simultaneous noise to simulate hearing loss.

Masking functions and fixed-signal functions for low-level 1000-Hz tones.

Masking functions and fixed-signal functions were constructed using a narrow range of pedestal intensities for 10-ms, 1000-Hz gated tones. Data from three experiments agreed with previously reported data, clearly demonstrating negative masking and the pedestal effect. The data extend earlier findings by showing (1) the resilience of the pedestal effect when a background noise masker is introduced; (2) a possible indifference of the fixed-signal function to stimulus duration; (3) the ability of a set of psychometric functions to produce both masking and fixed-signal functions; (4) depending on method, the impact of unit choice on the interpretation of both the pedestal effect and negative masking data. Results are discussed in relation to current psychophysical models, and suggest that accounting for the auditory system's sensitivity to differences in low-level sounds remains a challenge.

Distortion-product otoacoustic emission suppression tuning curves in hearing-impaired humans.

Distortion-product otoacoustic emission (DPOAE) suppression tuning curves (STCs) were measured in 65 hearing-impaired (HI) subjects at f(2) frequencies of 2.0, 2.8, 4.0, and 5.6 kHz and L(2) levels relative to sensation level (SL) from 10 dB to as much as 50 dB. Best frequency, cochlear-amplifier gain (tip-to-tail difference, T-T), and tuning (Q(ERB)) were estimated from STCs. As with normal-hearing (NH) subjects, T-T differences and Q(ERB) decreased as L(2) increased. T-T differences and Q(ERB) were reduced in HI ears (compared to normal) for conditions in which L(2) was fixed relative to behavioral threshold (dB SL). When STCs were compared with L(2) at constant sound pressure levels (dB SPL), differences between NH and HI subjects were reduced. The large effect of level and small effect of hearing loss were both confirmed by statistical analyses. Therefore, the magnitude of the differences in DPOAE STCs between NH and HI subjects is mainly dependent on the manner in which level (L(2)) is specified. Although this conclusion may appear to be at odds with previous, invasive measures of cochlear-response gain and tuning, the apparent inconsistency may be resolved when the manner of specifying stimulus level is taken into account.

Growth of suppression using distortion-product otoacoustic emission measurements in hearing-impaired humans.

Growth of distortion-product otoacoustic emission suppression was measured in 65 subjects with mild-to-moderate sensorineural hearing loss (HI). Measurements were made at four probe frequencies (f(2)) and up to five L(2) levels. Eleven suppressor frequencies (f(3)) were used for each f(2), L(2) combination. These data were compared to data from normal-hearing (NH) subjects (Gorga et al., 2011a). In both NH and HI subjects, growth of suppression depended on the relation between f(2) and f(3), such that the slope was close to one when f(3) ≈ f(2), steeper than one when f(3) < f(2), and shallower than one when f(3) > f(2). Differences in growth of suppression between NH and HI subjects were not observed for fixed f(2), L(2) combinations, however large differences were observed in suppressor "threshold" when compared at the same probe sensation level (dB SL). Smaller group differences were observed when compared at the same probe sound-pressure level (dB SPL). Therefore, the extent of these differences depended on how probe level (L(2)) was specified. When the results from NH and HI subjects are compared with each other and with psychophysical studies of masking, differences are observed that have implications for the remediation of mild-to-moderate hearing loss.

Temporal integration of loudness measured using categorical loudness scaling and matching procedures.

Temporal integration of loudness of 1 kHz tones with 5 and 200 ms durations was assessed in four subjects using two loudness measurement procedures: categorical loudness scaling (CLS) and loudness matching. CLS provides a reliable and efficient procedure for collecting data on the temporal integration of loudness and previously reported nonmonotonic behavior observed at mid-sound pressure level levels is replicated with this procedure. Stimuli that are assigned to the same category are effectively matched in loudness, allowing the measurement of temporal integration with CLS without curve-fitting, interpolation, or assumptions concerning the form of the loudness growth function.