Measures Of Loudness Growth Research Articles

Testing the Central Gain Model: Loudness Growth Correlates with Central Auditory Gain Enhancement in a Rodent Model of Hyperacusis

The central gain model of hyperacusis proposes that loss of auditory input can result in maladaptive neuronal gain increases in the central auditory system, leading to the over-amplification of sound-evoked activity and excessive loudness perception. Despite the attractiveness of this model, and supporting evidence for it, a critical test of the central gain theory requires that changes in sound-evoked activity be explicitly linked to perceptual alterations of loudness. Here we combined an operant conditioning task that uses a subject’s reaction time to auditory stimuli to produce reliable measures of loudness growth with chronic electrophysiological recordings from the auditory cortex and inferior colliculus of awake, behaviorally-phenotyped animals. In this manner, we could directly correlate daily assessments of loudness perception with neurophysiological measures of sound encoding within the same animal. We validated this novel psychophysical-electrophysiological paradigm with a salicylate-induced model of hearing loss and hyperacusis, as high doses of sodium salicylate reliably induce temporary hearing loss, neural hyperactivity, and auditory perceptual disruptions like tinnitus and hyperacusis. Salicylate induced parallel changes to loudness growth and evoked response-intensity functions consistent with temporary hearing loss and hyperacusis. Most importantly, we found that salicylate-mediated changes in loudness growth and sound-evoked activity were correlated within individual animals. These results provide strong support for the central gain model of hyperacusis and demonstrate the utility of using an experimental design that allows for within-subject comparison of behavioral and electrophysiological measures, thereby making inter-subject variability a strength rather than a limitation.

Repeated Measurement of Absolute and Relative Judgments of Loudness: Clinical Relevance for Prescriptive Fitting of Aided Target Gains for soft, Comfortable, and Loud, But Ok Sound Levels.

This study was undertaken with the purpose of streamlining clinical measures of loudness growth to facilitate and enhance prescriptive fitting of nonlinear hearing aids. Repeated measures of loudness at 500 and 3,000 Hz were obtained bilaterally at monthly intervals over a 6-month period from three groups of young adult listeners. All volunteers had normal audiometric hearing sensitivity and middle ear function, and all denied problems related to sound tolerance. Group 1 performed judgments of soft and loud, but OK for presentation of ascending sound levels. We defined these judgments operationally as absolute judgments of loudness. Group 2 initially performed loudness judgments across a continuum of seven loudness categories ranging from judgments of very soft to uncomfortably loud for presentation of ascending sound levels per the Contour Test of Loudness; we defined these judgments as relative judgments of loudness. In the same session, they then performed the absolute judgments for soft and loud, but OK sound levels. Group 3 performed the same set of loudness judgments as did group 2, but the task order was reversed such that they performed the absolute judgments initially within each test session followed by the relative judgments. The key findings from this study were as follows: (1) Within group, the absolute and relative tasks yielded clinically similar judgments for soft and for loud, but OK sound levels. These judgments were largely independent of task order, ear, frequency, or trial order within a given session. (2) Loudness judgments increased, on average, by ∼3 dB between the first and last test session, which is consistent with the commonly reported acclimatization effect reported for incremental changes in loudness discomfort levels as a consequence of chronic bilateral hearing aid use. (3) Measured and predicted comfortable judgments of loudness were in good agreement for the individual listener and for groups of listeners. These comfortable judgments bisect the measured levels judged for soft and for loud, but OK sounds. (4) Loudness judgments within the same loudness category varied across listeners within group by as much as 50 to 60 dB. Such large variation in judgments of loudness is problematic, especially because hearing-impaired listeners are known to exhibit similarly large ranges of intersubject response variation and, yet, poplar prescriptive fitting strategies continue to use average rather than individual loudness data to fit nonlinear hearing aids. The primary conclusions drawn from these findings are that reliable absolute judgments of soft and loud, but OK are clinically practical and economical to measure and, from these judgments, good estimates of comfortable loudness can also be predicted for individuals or for groups of listeners. Such loudness data, as measured as described in this report, offer promise for streamlining and enhancing prescriptive fitting of nonlinear hearing aids to target gain settings for soft (audible), comfortable, and loud, but OK (tolerable) sound inputs for the individual listener.

Loudness and auditory steady-state responses in normal-hearing subjects

This study evaluated the use of multiple auditory steady-state responses (ASSRs) to estimate the growth of loudness in listeners with normal hearing. Individual intensity functions were obtained from measures of loudness growth using the contour test and from the electrophysiological amplitude measures of multiple amplitude-modulated (77–105Hz) tones (500, 1000, 2000, and 4000Hz) simultaneously presented to both ears and recorded over the scalp. Slope analyses for the behavioural and electrophysiological intensity functions were separately performed. Response amplitudes of the ASSRs and loudness sensation judgements increase as the stimulus intensity increases for the four frequencies studied. A significant relationship was obtained between loudness and the ASSRs. The results of this study suggest that the amplitude of the ASSRs may be used to estimate loudness growth at least for individuals with normal hearing.

Predicting speech perception benefit from loudness growth measures and other map characteristics of the nucleus 22 implant.

Predicting speech perception benefit from loudness growth measures and other map characteristics of the nucleus 22 implant.

Use of a loudness model for hearing aid fitting. IV. Fitting hearing aids with multi-channel compression so as to restore 'normal' loudness for speech at different levels.

Many researchers have proposed that multi-channel compression hearing aids should process sounds so as to restore loudness perception to 'normal'. However, procedures for achieving this have generally been based on measurements or calculations using narrowband stimuli, and these procedures may not be accurate for broadband sounds such as speech. Here, a model for predicting loudness for people with cochlear hearing loss is used to calculate the frequency- and level-dependent gains that would be required to restore loudness perception to 'normal' for speech-like signals. The calculations are based entirely on the pure tone audiogram, and do not require measures of loudness growth. The model was applied to several different hypothetical hearing losses, varying in slope and severity. In each case, the model was used to calculate the insertion gains (IGs) that would be required as a function of frequency so that speech-shaped noise with a level of 65 dB SPL would evoke a specific loudness pattern matching that for a normal ear. A similar procedure was applied using speech-shaped noise with a level of 85 dB SPL (with the spectral characteristics of shouted speech). The results were used to derive functions relating the required IG to hearing loss for each audiometric frequency and each speech-shaped noise level. These functions were used in turn to derive compression ratios and gains for each channel of a multi-channel compression system. The derivations apply to systems with any number of channels. The outcome is a method than can be used for the initial fitting of multichannel compression hearing aids, so as to restore loudness perception to near 'normal' for broadband speech-like signals.

Assessing Growth of Loudness in Children by Cross-Modality Matching

This study examined the clinical feasibility, validity, and reliability of loudness growth assessment using cross-modality matching (CMM) between line length and loudness in 16 children 4 to 12 years old with normal hearing or bilateral sensorineural hearing losses ranging from moderate to severe in degree. Eight adult listeners with normal hearing were used as a comparison group. Loudness growth functions and real-ear measures were obtained for 500-Hz and 2,000-Hz narrowband noise stimuli for each individual. No significant differences were found between the loudness slope values for the adults and children with normal hearing. Loudness growth functions of the children with sensorineural hearing loss were significantly steeper (larger) than the slopes obtained from children with normal hearing. The numeric slope value of the loudness growth function became larger and more variable as children's hearing threshold increased and differed for children with similar thresholds. The loudness functions obtained for retested participants at two different test sessions were highly correlated. Real-ear measurements revealed that for equivalent input stimulus levels, significantly higher stimulus levels were present in the ear canals of children versus adults. Although adults and children with normal hearing had similar overall rates of loudness growth, discrete points along the loudness growth function were judged to be louder by the children. This preliminary study suggests that measures of loudness growth using CMM between line length and loudness are feasible, valid, and reliable in children with normal hearing or sensorineural hearing loss. The individual variability noted in slope values for children with hearing loss attests to the importance of subjective assessments of loudness. The protocol used in this study may have potential as a clinical tool for selecting and fitting amplification technology for children with hearing loss as young as 6 years.

Fitting Hearing Aids to Individual Loudness-Perception Measures

The purpose of this study was to compare the prescribed gain, compression ratios, compression thresholds, and the relative predicted speech intelligibility (Speech Intelligibility Index [SII], American National Standards Institute 3.79, proposed) provided by four strategies proposed for selecting hearing aid parameters for low-threshold compression hearing instruments and by a traditional threshold-based hearing aid fitting procedure. The strategies used were Desired Sensation Level Input/Output (DSLTM[i/o]; Cornelisse, Seewald, & Jamieson, 1994), Visual Input-Output Locator Algorithm (VIOLA; Cox, 1994), FIG6 strategy (Killion, Reference Note 2), Ricketts and Bentler strategy (RAB), and a threshold-based hearing aid fitting procedure (National Acoustics Laboratories-Revised [NAL-R]; Byrne & Dillion, 1986). These new strategies have been suggested as alternatives to threshold-based strategies, which do not provide the varying amounts of target gain, as a function of input level, necessary to fit low-threshold compression hearing aids. The electroacoustic prescriptions and the predicted speech intelligibility were calculated across all five fitting strategies for 20 subjects. The threshold and loudness growth information used for each fitting was reported previously (Ricketts & Bentler, in press). Comparison across prescriptions revealed that the NAL-R strategy (due to the linear gain provided) prescribed the least gain for low-level inputs and the greatest gain for high-level inputs. Gain comparisons across fitting by loudness (FBL) strategies revealed a more shallow frequency response slope for strategies that require individual measures of loudness growth (RAB, VIOLA) in comparison with strategies that assumed average data (FIG6, DSLTM[i/o]). SII results revealed greater predicted speech intelligibility for the FIG6 and the DSLTM[i/o] compared with the NAL-R, RAB, and VIOLA. These differences were most apparent in noise backgrounds and least evident when loudness differences were minimized. It appears that differences in SII scores across the FBL fitting strategies are due, in part, to differences in the loudness of the output signal. It is assumed that differences in high-frequency shaping may also be a factor. These data do not appear to support the use of additional clinical time to obtain individual loudness growth measures. However, due to the fact that SII results are based on average performance, it is difficult to predict whether differences across these fitting strategies would be realized in actual measures of speech intelligibility or sound quality on an individual basis.

The effect of test signal type and bandwidth on the categorical scaling of loudness

Recently several methods for obtaining clinical measures of loudness growth through the use of categorical scaling (CS) have been proposed for the selection of hearing aids. These methods use differing test signals or suggest frequency-specific level corrections in an attempt to reflect the loudness perception of hearing aid-processed speech. While some decisions regarding the stimuli utilized for loudness perception procedures are based on measured relationships to speech signals, the effect on loudness perception of changing signal type and bandwidth (as measured by CS) remains unclear. The relationships between the CS loudness growth of signals of differing type, (pure tones, noise bands, filtered/temporally inverted/passband speech) and bandwidth were examined for subjects with both normal and impaired hearing. Results suggest that when the bandwidth is similar (e.g., pure tone and 1/3 oct), signal type does not have significant bearing on loudness perception. As expected, increasing the bandwidth beyond the critical band affected loudness growth, as wideband speech stimuli were judged to be significantly louder than narrow-band speech at equivalent overall sound levels. In this investigation, similar loudness growth patterns were noted across category ratings for all test signal bandwidths. In contrast, loudness growth data obtained using an intelligible speech signal [Cox et al., The American Academy of Audiology (1994a)], revealed loudness growth patterns for speech were fundamentally different than those obtained for tones. Implications for hearing aid fitting strategies are discussed.

Monaural and binaural auditory brainstem responses in relation to the psychophysical loudness growth function.

Electrophysiological measures of the brainstem response to auditory stimuli permit comparisons to be made between latency shifts across intensity increments and psychophysical measures of loudness growth. Monaural comparisons leave much room for uncertainty in the interpretation of the nature of the relationship between the two response modes. A more definitive method for examining this relationship is to compare the monaural and binaural data obtained from psychophysical and electrophysiological measures. It is shown here that, while the brainstem electrophysiological response to intensity changes can be described by a power function, the latency of the neural response does not provide a direct link to the process of loudness summation or to the psychophysical response to loudness growth.