Temporal loudness integration and spectral loudness summation in normal-hearing and hearing-impaired listeners

On the Effect of High Stimulation Rates on Temporal Loudness Integration in Cochlear Implant Users

Long stimuli have lower detection thresholds or are perceived louder than short stimuli with the same intensity, an effect known as temporal loudness integration (TLI). In electric hearing, TLI for pulse trains with a fixed rate but varying number of pulses, i.e. stimulus duration, has mainly been investigated at clinically used stimulation rates. To study the effect of an overall effective stimulation rate at 100% channel crosstalk, we investigated TLI with (a) a clinically used single-channel stimulation rate of 1,500 pps and (b) a high stimulation rate of 18,000 pps, both for an apical and a basal electrode. Thresholds (THR), a line of equal loudness (BAL), and maximum acceptable levels (MALs) were measured in 10 MED-EL cochlear implant users. Stimulus durations varied from a single pulse to 300 ms long pulse trains. At 18,000 pps, the dynamic range (DR) increased by 7.36 ± 3.16  dB for the 300 ms pulse train. Amplitudes at THR, BAL, and MAL decreased monotonically with increasing stimulus duration. The decline was fitted with high accuracy with a power law function (R 2 = 0.94 ± 0.06 ). Threshold slopes were - 1.05 ± 0.36 and - 1.66 ± 0.30  dB per doubling of duration for the low and high rate, respectively, and were shallower than for acoustic hearing. The electrode location did not affect the amplitudes or slopes of the TLI curves. THR, BAL, and MAL were always lower for the higher rate and the DR was larger at the higher rate at all measured durations.

Relationship between Behavioral and Objective Measures of Sound Intensity in Normal-Hearing Listeners and Hearing-Aid Users: A Pilot Study

Background: For hearing-impaired individuals, hearing aids are clinically fit according to subjective measures of threshold and loudness. The goal of this study was to evaluate objective measures of loudness perception that might benefit hearing aid fitting. Method: Seventeen adult hearing aid users and 17 normal-hearing adults participated in the study. Outcome measures including categorical loudness scaling, cortical auditory evoked potentials (CAEPs), and pupillometry. Stimuli were 1-kHz tone bursts presented at 40, 60, and 80 dBA. Results: Categorical loudness scaling showed that loudness significantly increased with intensity for all participants (p < 0.05). For CAEPs, high intensity was associated with greater P1, N1, and P2 peak amplitude for all listeners (p < 0.05); a significant but small effect of hearing aid amplification was observed. For all participants, pupillometry showed significant effects of high intensity on pupil dilation (p < 0.05); there was no significant effect of hearing aid amplification. A Focused Principal Component analysis revealed significant correlations between subjective loudness and some of the objective measures. Conclusion: The present data suggest that intensity had a significant impact on loudness perception, CAEPs, and pupil response. The correlations suggest that pupillometry and/or CAEPs may be useful in determining comfortable amplification for hearing aids.

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.

Uni- and bilateral spectral loudness summation and binaural loudness summation with loudness matching and categorical loudness scaling

OBJECTIVE

Current hearing aid prescription rules assume that spectral loudness summation decreases with hearing impairment and that binaural loudness summation is independent of hearing loss and signal bandwidth. Previous studies have shown that these assumptions might be incorrect. Spectral loudness summation was measured and compared for loudness scaling and loudness matching.

DESIGN

In this study, the effect of bandwidth on binaural summation was investigated by comparing loudness perception of low-pass filtered, high-pass filtered, and broadband pink noise at 35 Categorical Units for both unilateral and bilateral presentation.

STUDY SAMPLE

Sixteen hearing-impaired listeners.

RESULTS

The results show that loudness differences between the three signals are different for bilateral presentation than for unilateral presentation. In specific, binaural loudness summation is larger for the low-pass filtered pink noise than for the high-pass filtered pink noise. Finally, individual variability in loudness perception near loudness discomfort level was found to be very large.

CONCLUSIONS

Loudness matching is offered as a fast and reliable method to measure individual loudness perception. As discomfort with loud sounds is one of the major problems encountered by hearing aid users, measurement of individual loudness perception could improve hearing aid fitting substantially.

Potential Consequences of Spectral and Binaural Loudness Summation for Bilateral Hearing Aid Fitting

Aversiveness of loud sounds is a frequent complaint by hearing aid users, especially when fitted bilaterally. This study investigates whether loudness summation can be held responsible for this finding. Two aspects of loudness summation should be taken into account: spectral loudness summation for broadband signals and binaural loudness summation for signals that are presented binaurally. In this study, the effect of different symmetrical hearing losses was studied. Measurements were obtained with the widely used technique of Adaptive Categorical Loudness Scaling. For large bandwidths, spectral loudness summation for hearing-impaired listeners was found to be greater than that for normal-hearing listeners, both for monaurally and binaurally presented signals. For binaural loudness summation, the effect of hearing loss was not significant. In all cases, individual differences were substantial.

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.

Loudness summation of equal loud narrowband signals in normal-hearing and hearing-impaired listeners

OBJECTIVE

Loudness perception of binaural broadband signals, e.g. speech shaped noise, shows large individual differences using frequency-dependent amplification which was adjusted to restore the loudness perception of monaural narrowband signals in hearing-impaired (HI) listeners. To better understand and quantify this highly individual effect, loudness perception of broadband stimuli consisting of a number of spectrally separated narrowband components which where individually adjusted to equal loudness is of interest.

DESIGN

Based on categorical loudness scaling, the loudness of an equal categorical loudness noise (ECLN) consisting of six third-octave noises was assessed. For loudness categories "medium" und "very loud" the required narrowband loudness was analysed.

STUDY SAMPLE

Nine normal-hearing (NH) and ten HI listeners.

RESULTS

HI listeners showed lower narrowband loudness values compared to NH listeners, indicating an increased spectral loudness summation. More than 50% of the HI listeners showed higher binaural spectral loudness summation compared to NH listeners. The amount of binaural spectral loudness summation was highly correlated (r² = 0.92) with the loudness level at "very loud" of aided speech shaped noise.

CONCLUSIONS

The suggested ECLN measurement is suited to assess individual (binaural) broadband loudness in aided conditions, providing valuable information for hearing-aid fitting.

Spectral and binaural loudness summation for hearing-impaired listeners

Sensorineural hearing loss typically results in a steepened loudness function and a reduced dynamic range from elevated thresholds to uncomfortably loud levels for narrowband and broadband signals. Restoring narrowband loudness perception for hearing-impaired (HI) listeners can lead to overly loud perception of broadband signals and it is unclear how binaural presentation affects loudness perception in this case. Here, loudness perception quantified by categorical loudness scaling for nine normal-hearing (NH) and ten HI listeners was compared for signals with different bandwidth and different spectral shape in monaural and in binaural conditions. For the HI listeners, frequency- and level-dependent amplification was used to match the narrowband monaural loudness functions of the NH listeners. The average loudness functions for NH and HI listeners showed good agreement for monaural broadband signals. However, HI listeners showed substantially greater loudness for binaural broadband signals than NH listeners: on average a 14.1 dB lower level was required to reach "very loud" (range 30.8 to -3.7 dB). Overall, with narrowband loudness compensation, a given binaural loudness for broadband signals above "medium loud" was reached at systematically lower levels for HI than for NH listeners. Such increased binaural loudness summation was not found for loudness categories below "medium loud" or for narrowband signals. Large individual variations in the increased loudness summation were observed and could not be explained by the audiogram or the narrowband loudness functions.

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 takes place in the primary auditory cortex

Auditory functional magnetic resonance imaging (fMRI) was used to assess neural activation in the human auditory brainstem (AB) and cortex (AC) as a function of bandwidth (BW). We recorded brain activation of 22 normal hearing listeners induced by band pass filtered pink noise stimuli with equal sound pressure level of 70 dB SPL. Tested bandwidths were 50, 500, 1,500, 3,000, 6,000, and 8,000 Hz. The center frequency was 4,000 Hz. Categorical loudness scaling had been performed in a silent booth with all of these stimuli. Loudness as a function of bandwidth followed a concave-shaped curve which reflected the influence of spectral loudness summation (SLS) for higher BW and the influence of large amplitude fluctuations for very low BW, which itself could be explained by peak-listening. While neural activation of the AB, as measured by the percent signal change from baseline (PSC), was tuned to the physical BW of the stimuli in a straight linear fashion, the trend of perceived loudness as a function of BW was reflected in several aspects by corresponding neural activation in the primary auditory cortex (PAC). Finally, from the absolute differences of the PSC between PAC and AB, gains in perceived loudness associated with SLS and the effect of large amplitude fluctuations could be predicted with an accuracy of 1-2 dB for the whole group of participants.

Spectral loudness summation as a function of duration for hearing-impaired listeners

Spectral loudness summation was measured for 10- and 1000-ms long bandpass-noise signals with bandwidths in the range of 0.2 to 6.4 kHz centered at 2 kHz for nine listeners with hearing impairment of primarily cochlear origin. Loudness matches between signals with the same duration and different bandwidth were obtained using an adaptive two-interval, two-alternative forced-choice procedure with interleaved tracks. The 3200-Hz wide reference signal had a level of 45 dB or 65 dB SPL. Every signal was individually frequency equalized prior to presentation in order to ensure audibility of all spectral components for the two reference input levels. Generally the same amount of spectral loudness summation for 10- and 1000-ms long signals was obtained for both reference levels. However, some hearing-impaired listeners show, similarly to normal-hearing listeners, a larger spectral loudness summation for short than for long duration signals, indicating that duration effects in spectral loudness summation are caused by retrocochlear processes.

Spectral loudness summation as a function of duration

Loudness was measured as a function of signal bandwidth for 10-, 100-, and 1000-ms-long signals. The test and reference signals were bandpass-filtered noise spectrally centered at 2 kHz. The bandwidth of the test signal was varied from 200 to 6400 Hz. The reference signal had a bandwidth of 3200 Hz. The reference levels were 45, 55, and 65 dB SPL. The level to produce equal loudness was measured with an adaptive, two-interval, two-alternative forced-choice procedure. A loudness matching procedure was used, where the tracks for all signal pairs to be compared were interleaved. Mean results for nine normal-hearing subjects showed that the magnitude of spectral loudness summation depends on signal duration. For all reference levels, a 6- to 8-dB larger level difference between equally loud signals with the smallest (delta f = 200 Hz) and largest (delta f = 6400 Hz) bandwidth is found for 10-ms-long signals than for the 1000-ms-long signals. The duration effect slightly decreases with increasing reference loudness. As a consequence, loudness models should include a duration-dependent compression stage. Alternatively, if a fixed loudness ratio between signals of different duration is assumed, this loudness ratio should depend on the signal spectrum.