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PubMed1996

Compression? Yes, but for low or high frequencies, for low or high intensities, and with what response times?

Several rationales for using compression in hearing aids are outlined. These rationales comprise discomfort avoidance, loudness normalization, noise reduction, short term signal dynamic range reduction, empirically determined compression, and long-term signal dynamic range reduction. The compression systems needed to implement each of these differ greatly, and these differences can be viewed as differences in the frequency range undergoing most compression, the intensity range undergoing most compression, and the speed at which the compressor(s) operate. A classification system along these lines is introduced and examples of currently available hearing aids falling into each category are given. The effects of each type of compression on speech intelligibility is investigated via a review of published research. The results of this indicate that, for speech in quiet at a comfortable level, no compression scheme yet tested offers better intelligibility than individually selected linear amplification. If input level is then decreased and the aid wearer is prevented from adjusting the volume control, many types of compression provide intelligibility superior to that available from linear amplification. In broadband noise, only one system, containing wideband compression followed by fast acting high-frequency compression, has so far been shown to provide significant intelligibility advantages.

Equipment Design↗
PubMed1996

Binaural summation of the acoustic reflex.

OBJECTIVE: The ways in which summation of energy or of information occurs have long been used to explore sensory mechanisms. In the case of the acoustic reflex, some binaural summation is known to occur, but both data and specification of method have been sketchy. Accurate estimates of mean and standard deviation were therefore sought to compare binaural acoustic reflex summation (BARS) with binaural loudness summation (BLS) to determine whether these have a common basis. DESIGN: A specified method was developed for determining reliable acoustic reflex values from admittance/intensity functions. Subjects were 34 university students; the ages ranged from 18 through 25 yr. For each, the contralateral component of the binaural stimulus was presented at a level above the ipsilateral component corresponding to the difference in monaural reflex thresholds ("physiologically equivalent"). RESULTS: BARS had a mean of 4.4 dB (SD = 3.5 dB), which was significantly different from the BLS (mean = 7.6 dB, SD = 1.2 dB). The contralateral-ipsilateral difference had a mean of 11.0 dB (SD = 5.1 dB). The BARS estimate was not appreciably larger than that found in studies lacking correction for physiologic equivalence. CONCLUSIONS: Although the presence of a contralateral component elicits a summation or facilitation effect, the particular intensity value contributes little to the magnitude of that effect.

Adolescent↗
PubMed1996

Effects of acclimatization and deprivation on non-speech auditory abilities.

This article reviews the evidence for acclimatization and deprivation with respect to non-speech auditory abilities. Although this subject has not been studied extensively, clear evidence exists for acclimatization and/or deprivation effects on intensity discrimination, binaural masking level difference, and auditory localization and lateralization. There is also some argument for such effects with regard to changes in tolerance for intense sounds or preferred levels of amplification. However, the main evidence for these effects, changes in loudness discomfort levels with repeated testing, may reasonably be explained as procedural or task-related effects rather than changes in auditory abilities. On the other hand, the successful use of tinnitus maskers to treat hyperacusis suggests that particularly low tolerance levels may be improved by exposure to certain types of auditory stimulation. Overall, this retrospective review of changes in non-speech auditory abilities, associated with the presence or absence of listening experience, indicates that acclimatization or deprivation effects may have influenced the results of some of the experiments reviewed. This suggests that experiments designed to study acclimatization or deprivation are timely and useful. In addition, acclimatization and deprivation are potential variables that should be considered, and preferably controlled, within experiments on auditory abilities. Clinically, the review adds weight to the argument for considering acclimatization and/or deprivation in hearing aid fitting and evaluation.

Functional Laterality↗
PubMed1997

Pulse rate matching by cochlear implant patients: effects of loudness randomization and electrode position.

OBJECTIVE: To assess the accuracy with which cochlear implant patients are able to match two stimuli on the basis of pulse rate pitch. DESIGN: Patients were required to adjust the pulse rate of a comparison stimulus to match that of a fixed reference stimulus. The comparison and the reference stimuli differed in loudness or were presented to different electrodes. RESULTS: Patients were able to match stimuli on the basis of pulse rate, with varying degrees of accuracy. Deviations from the target and the amount of variability were greater when stimuli were presented to different electrodes. The results also provide evidence regarding level-dependent pitch shifts. CONCLUSIONS: Because of methodological limitations, conclusions regarding pitch equivalence are limited. However, patients vary significantly in their ability to utilize temporal information.

Adult↗
PubMed1997

The relationship between loudness intensity functions and the click-ABR wave V latency.

OBJECTIVE: To assess the relationship of loudness growth and the click-evoked auditory brain stem response (ABR) wave V latency-intensity function (LIF) in listeners with normal hearing or cochlear hearing loss. The effect of hearing loss configuration on the intensity functions was also examined. DESIGN: Behavioral and electrophysiological intensity functions were obtained using click stimuli of comparable intensities in listeners with normal hearing (Group I; n = 10), and cochlear hearing loss of flat (Group II; n = 10) or sloping (Group III; n = 10) configurations. Individual intensity functions were obtained from measures of loudness growth using the psychophysical methods of absolute magnitude estimation and production of loudness (geometrically averaged to provide the measured loudness function), and from the wave V latency measures of the ABR. RESULTS: Slope analyses for the behavioral and electrophysiological intensity functions were separately performed by group. The loudness growth functions for the groups with cochlear hearing loss approximated the normal function at high intensities, with overall slope values consistent with those reported from previous psychophysical research. The ABR wave V LIF for the group with a flat configuration of cochlear hearing loss approximated the normal function at high intensities, and was displaced parallel to the normal function for the group with sloping configuration. The relationship between the behavioral and electrophysiological intensity functions was examined at individual intensities across the range of the functions for each subject. A significant relationship was obtained between loudness and the ABR wave V LIFs for the groups with normal hearing and flat configuration of cochlear hearing loss; the association was not significant (p = 0.10) for the group with a sloping configuration of cochlear hearing loss. CONCLUSION: The results of this study established a relationship between loudness and the ABR wave V latency for listeners with normal hearing, and flat cochlear hearing loss. In listeners with a sloping configuration of cochlear hearing loss, the relationship was not significant. This suggests that the click-evoked ABR may be used to estimate loudness growth at least for individuals with normal hearing and those with a flat configuration of cochlear hearing loss. Predictive equations were derived to estimate loudness growth for these groups. The use of frequency-specific stimuli may provide more precise information on the nature of the relationship between loudness growth and the ABR wave V latency, particularly for listeners with sloping configurations of cochlear hearing loss.

Acoustic Stimulation↗
PubMed1998

The National Acoustic Laboratories' procedure for selecting the saturation sound pressure level of hearing aids: experimental validation.

OBJECTIVE: The primary aim of this study is to evaluate the accuracy of a new procedure for selecting the saturation sound pressure level (SSPL) of hearing aids. Secondary aims are to investigate what limits the minimum SSPL that is acceptable to clients and whether the type of limiting (peak clipping or compression limiting) affects the SSPL required. DESIGN: The study comprised two experiments. In the first, subjects increased the SSPL of a laboratory master hearing aid until they experienced loudness discomfort and decreased it until the sound became less acceptable in some way. In the second study, subjects wore multi-memory programmable hearing aids in their own environments and reported which of the two programs, differing only in SSPL setting, provided the more acceptable sound quality and comfort. RESULTS: The theoretical procedure being investigated prescribed SSPLs that were within the acceptable range for 86% of the subjects in the laboratory study and for 63% of the subjects in the field experiment. On average, the theoretical predictions were neither too high nor too low. Incorporating individual measurements of loudness discomfort level into the prescription formula increased accuracy by such a small amount that it was not considered worthwhile. For a compression limiting hearing aid, the first thing that subjects noticed as SSPL was reduced was inadequate loudness. For the peak clipping hearing aid, however, both inadequate loudness and perception of distortion limited the acceptable SSPL range. CONCLUSION: The theoretical procedure provides a good initial prescription of three frequency average SSPL, but it is still essential to evaluate the fitting and, if necessary, fine tune the individual's hearing aid. Compression limiting hearing aids can have slightly lower SSPL settings than peak clipping hearing aids for the same acceptability.

Acoustic Stimulation↗
PubMed1999

Client preferences for compression threshold in single-channel wide dynamic range compression hearing aids.

OBJECTIVE: Compression in hearing aids can be applied with low compression ratios over a wide range of input levels, but reverts to linear amplification below the compression threshold (CT). In this study, we aimed to determine which of two CTs was preferred by subjects as they used their hearing aids in their own environments, and whether they would prefer to have no low ratio compression at all. DESIGN: Subjects were fitted with a multimemory hearing aid incorporating input controlled compression with a 2:1 compression ratio and output controlled compression limiting. The two memories contained identical programs except that they differed in CT. Sixteen mild to moderately sensorineurally hearing-impaired subjects compared low (approximately 40 dB SPL) and moderate (approximately 65 dB SPL) CTs over 2 mo of field trials using hand held remote controls to switch between the alternatives. In a third month's trial, the preferred option (which also included output controlled compression limiting) was compared with compression limiting alone. RESULTS: The higher CT was preferred by 14 of the subjects. The combination of input compression and output compression limiting was preferred to compression limiting alone by 14 of the subjects. CONCLUSIONS: Several real world advantages of frequency independent 2:1 compression with a CT of about 65 dB SPL were demonstrated over linear amplification. Extending the compression to much lower input levels appears to carry more disadvantages than advantages, at least for clients with mild and moderate hearing losses, when fitted with single-channel compression aids with a 2:1 compression ratio.

Aged↗
PubMed1999

Cross-modality matching: a tool for measuring loudness in sensorineural impairment.

OBJECTIVE: The main goal of this study was to establish the viability of cross-modality matching (CMM) for the measurement of individual loudness functions in sensorineural-impaired hearing. To achieve this goal, CMM was tested rigorously to assess four measurement requirements: 1) internal consistency; 2) small relative variance across listeners; 3) test-retest reliability; and 4) data validity. DESIGN: The measurements involved two sensory continua: perceived length and loudness. Sensation-magnitude functions were generated for all listeners from absolute magnitude estimation (AME) of perceived length, from CMM between loudness and perceived length, and from AME and absolute magnitude production (AMP) of loudness. A total of 211 listeners, 83 with normal hearing at the stimulus frequency and 128 with a diagnosis of cochlear impairment of long duration, performed all four magnitude-scaling tasks. Supplementary loudness matches also were obtained. RESULTS: Based on the analysis of data, the following results were obtained. First, in accord with loudness measures in normal hearing, loudness measures in cochlear-impaired hearing showed that individuals with bilateral impairments can produce internally consistent loudness data. Second, over the stimulus range where cochlear impairment steepens the loudness function, in a log-log plot loudness slopes derived from CMM, like those obtained from AME and AMP of loudness, were larger in cochlear-impaired hearing than in normal hearing. However, the results of CMM were typically less variable than those obtained from AME and AMP of loudness, permitting a clear-cut distinction between loudness growth rates (slopes) in normal and cochlear-impaired hearing. Third, the results showed that within a cochlear-impaired population, much of the intersubject variability of the slope of the loudness function can be ascribed to the heterogeneity of individual thresholds. Consistent with loudness matching, the size of the slopes increased with the degree of hearing loss. The dependence of the size of the slopes on the degree of hearing loss was observed for hearing losses as large as 75 dB. Fourth, test-retest reliability data for 36 listeners showed that CMM can yield reliable and stable loudness-growth measures in cochlear-impaired hearing over the long term. Finally, equal-sensation matches obtained directly from loudness matching closely agreed with those obtained indirectly from magnitude scaling, indicating that CMM is a valid method for the measurement of loudness magnitudes. CONCLUSIONS: Taken together, the results demonstrate that CMM can yield stable, accurate, and robust loudness growth measures in cochlear-impaired hearing. Given its apparent reliability, validity, and ease of application, CMM has the potential to become a powerful tool for assessing the growth of loudness in a clinical population. Loudness-level functions derived from CMM may well be important for determining the frequency-gain response of a hearing aid that most closely compensates for the distorted input-output function of the impaired auditory system.

Adolescent↗
PubMed2000

Monaural and binaural loudness measures in cochlear implant users with contralateral residual hearing.

OBJECTIVE: The aim was to measure the loudness of monaural and binaural stimuli in a group of cochlear implant users who had residual hearing in the nonimplanted ear, and to consider the implications of these measures for a binaural fitting consisting of a hearing aid and an implant in opposite ears. Three independent hypotheses were addressed: that the shapes of the electric and acoustic loudness growth functions would be similar, although the dynamic ranges would differ; that standard implant and hearing aid fittings would result in substantial loudness mismatches between the acoustic and electric signals; and that loudness summation would occur for binaural combinations of electric and acoustic signals. DESIGN: A modified version of the "Loudness Growth in 1/2-Octave Bands" method (Allen, Hall, & Jeng, 1990) was used to measure loudness growth for each ear of nine subjects. At the time of the experiment, the subject group included all implant users in Melbourne and Denver who were available for research and who also had sufficient residual hearing to use a hearing aid in the nonimplanted ear. Five acoustic frequencies and five electrodes were measured for each subject. The same subjects also estimated the loudness of a set of stimuli including monaural and binaural signals chosen to cover the loudness range from very soft to loud. RESULTS: The shapes of the averaged loudness growth functions were similar in impaired and electrically stimulated ears, although the shapes of iso-loudness curves were quite different in the two ears, and dynamic ranges varied considerably. Calculations based on the psychophysical data demonstrated that standard fitting procedures for cochlear implants and hearing aids lead to a complex pattern of loudness differences between the ears. A substantial amount of loudness summation was observed for the binaural stimuli, with most summation occurring when the acoustic and electric components were of equal loudness. This is consistent with observations for subjects with normal hearing and subjects with bilaterally impaired hearing. CONCLUSIONS: These experiments provide data on which criteria and methods for the binaural fitting of cochlear implants and hearing aids may be based. It is unlikely that standard monaural fitting methods for cochlear implants and hearing aids will result in balanced loudness between the two ears across a reasonably broad range of frequencies and levels. It is also likely that output levels of both devices will need to be reduced relative to a monaural fitting to compensate for the binaural summation of loudness in some listeners.

Adult↗
PubMed2000

Comparison of linear gain and wide dynamic range compression hearing aid circuits II: aided loudness measures.

OBJECTIVES: The goal of this study was to test the theoretical advantages of a single-channel wide dynamic range compression (WDRC) circuit fitted using the DSL method for increased dynamic range and normalized loudness growth. DESIGN: Ten adolescents and young adults with moderate to severe sensorineural hearing loss were fitted monaurally with the Siemens Viva 2 Pro behind-the-ear instrument set to DSL 4.0 targets for both linear gain and WDRC processing. Threshold, upper limit of comfort and loudness growth were measured in the unaided, linear gain and WDRC conditions for warble tones, environmental sounds and speech. Twelve adult listeners with normal hearing also were tested monaurally in the unaided condition to provide normative data for comparison purposes. RESULTS: The WDRC hearing aid provided a greater input dynamic range than the linear circuit for all stimuli. The dynamic range was normalized for more subjects with the WDRC than the linear hearing aid. In addition, exponential loudness growth functions fitted to the loudness growth data showed that, on average, loudness growth was more normalized with the WDRC hearing aid fitted to DSL[i/o] targets than the linear hearing aid fitted to DSL[i/o] targets. CONCLUSIONS: WDRC processing, fitted using the DSL[i/o] method, has potential applications in hearing aid fittings for listeners with moderate to severe hearing loss because it provides an audible, comfortable and tolerable amplified signal across a wider range of inputs than linear gain processing, without the need for volume control adjustments.

Adolescent↗
PubMed2000

Effects of dynamic range and amplitude mapping on phoneme recognition in Nucleus-22 cochlear implant users.

OBJECTIVE: To determine the consequences for phoneme recognition of errors in setting threshold and loudness levels in cochlear implant listeners using a 4-channel continuous interleaved sampling (CIS) speech processor. DESIGN: Three Nucleus-22 cochlear implant listeners, who normally used the SPEAK speech processing strategy participated in this study. An experimental 4-channel CIS speech processor was implemented in each listener as follows. Speech signals were band-pass filtered into four broad frequency bands and the temporal envelope of the signal in each band was extracted by half-wave rectification and low-pass filtering. A power function was used to convert the extracted acoustic amplitudes to electric currents. The electric currents were dependent on the exponent of the mapping power function and the electrode dynamic range, which was determined by the minimum and maximum stimulation levels. In the baseline condition, the minimum and maximum stimulation levels were defined as the psychophysically measured threshold level (T-level) and maximum comfortable level (C-level). In the experimental conditions, the maximum stimulation levels were fixed at the C-level and the dynamic range (in dB) was changed by varying the minimum stimulation levels on all electrodes. This manipulation simulates the effect of an erroneous measurement of the T-level. Phoneme recognition was obtained as the dynamic range of electrodes was changed from 1 dB to 20 dB and as the exponent of the power-law amplitude mapping function was changed from 0.1 to 0.4. RESULTS: For each mapping condition, the electric dynamic range had a significant, but weak effect on vowel and consonant recognition. For a strong compression (p = 0.1), best vowel and consonant scores were obtained with a large dynamic range (12 dB). When the exponent of the mapping function was changed to 0.2 and 0.4, the dynamic range producing the highest scores decreased to 6 dB and 3 dB, respectively. CONCLUSIONS: Phoneme recognition with a 4-channel CIS strategy was only mildly affected by large changes in both electric threshold and loudness mapping. Errors in threshold by a factor of 2 (6 dB) and in the loudness mapping exponent by a factor of 2 were required to produce a significant decrease in performance. In these extreme conditions, the effect of the electric dynamic range on phoneme recognition could be due to two independent factors: abnormal loudness growth and a reduction in the number of discriminable intensity steps. The decrease in performance caused by a reduced electric dynamic range can be compensated by a more expansive power-law mapping function, as long as the number of discriminable intensity steps is moderately large (e.g., >8).

Acoustic Stimulation↗
PubMed2000

Duration, compression, and the aided loudness discomfort level.

OBJECTIVE: The purpose of this investigation is to determine how the unaided and aided loudness discomfort level (LDL) varies with the duration of the input signal and whether the electroacoustic characteristics of compression circuits affect this relationship in a manner that may alter the listener's dynamic range for short duration sounds. DESIGN: Ten hearing-impaired and 20 normal-hearing listeners participated. LDLs were determined for noise bursts of durations ranging in six steps from 32 to 1024 msec, using a two-alternative, forced-choice adaptive tracking procedure in which input level varied until LDL was achieved. LDLs were also obtained for continuous discourse, using a clinical procedure. Subjects were also given the opportunity to self adjust maximum output SPL to their LDL using either output limiting or volume controls in response to fixed 90 dB SPL noise bursts. Testing was conducted unaided and with hearing aids representing two analog (output compression limiting, wide dynamic range compression) and four digital compression circuits. Primary circuit contrasts included compression threshold, compression ratio, attack time and the presence or absence of unity gain at high levels. RESULTS: For the unaided condition, both normal-hearing and hearing-impaired subjects showed increasing LDLs with decreasing signal duration. Under aided conditions, circuits with compression thresholds of 45 to 50 dB SPL and compression ratios of 2:1 produced LDL functions that were similar in slope to the impaired listener's unaided functions. Slopes were steeper when the attack time was slow (128 msec) than when it was fast (2 msec). Circuits with compression ratios of 8:1 produced flat LDL duration functions (i.e., a loss of duration-dependent effects). Similar duration-dependent LDL effects were also observed when subjects adjusted their own hearing aid output characteristics in response to 90 dB noise bursts. CONCLUSION: For the unaided condition, results suggest that normal-hearing and hearing-impaired listeners can tolerate short duration sounds at higher levels than long duration sounds, a finding that has implications for hearing aid design. Circuits that preserve the relationship between duration and LDL should allow brief phonemes to be presented at higher levels without discomfort than circuits that do not, possibly resulting in greater audibility or speech recognition. Current results suggest that circuits with low compression thresholds, low compression ratios, and slow attack times might accomplish this objective better than circuits with high compression thresholds, high compression ratios and fast attack times.

Adult↗
PubMed2001

A comparison of two loudness balancing tasks in cochlear implant subjects using bipolar stimulation.

OBJECTIVE: In this study, the accuracy of independent measurement of the loudness of different electrodes in a cochlear implant (the "reference" method) was compared with the accuracy of measurements that depend on the results of previous measurements (the "adjacent" method) by evaluating the similarity between and the slopes of the loudness balance curves, and the variability in the measured loudness balance values. DESIGN: The two methods of loudness balancing differed only in the reference electrode used. In the adjacent method, the loudness of the test electrode was sequentially adjusted to match the loudness of an adjacent reference electrode, whereas in the reference method, the loudness of all test electrodes was adjusted to match that of a common reference electrode. Five subjects implanted with the Nucleus 22 device completed both methods of loudness balancing for all of their functioning electrodes. Each test/reference electrode pair was loudness balanced six times to assess the variability of the two methods. RESULTS: The loudness balance curves for the two methods were statistically correlated (p < 0.001) for all subjects. The slopes of the regression lines for the loudness balance curves were statistically different from zero (p < 0.05) for roughly half of the subjects for each method. A sign test indicated statistically different means for the basal set and apical set of measurements for only one subject for both methods. The variance in the measured values across electrodes for the reference method was significantly greater for three of the five subjects (p < 0.01). CONCLUSIONS: It was hypothesized that because of its dependence on previously measured values, the adjacent method could be susceptible to "drift," i.e., a shift in the overall loudness to which the electrodes are balanced. However, none of the statistical measures employed to test for drift indicated that the adjacent method was more susceptible to drift than the reference method, nor were the responses to the adjacent method more variable. Thus, based on these results, dependent measurements do not seem to be less accurate than independent measurements. The relatively higher variance for the reference method in some subjects may be due to the difficulty of comparing the loudness of stimuli that are far apart in pitch.

Adult↗
PubMed2001

The selection and validation of output sound pressure level in multichannel hearing aids.

OBJECTIVE: To validate the Australian National Acoustic Laboratories' (NAL) procedure for prescribing output sound pressure level (OSPL) for multichannel hearing aids (Dillon & Storey, 1998) DESIGN: The NAL OSPL prescriptive procedure for multichannel hearing aids was used to calculate Predicted OSPL, Predicted Maximum Acceptable OSPL and Predicted Minimum Acceptable OSPL for 20 subjects with sensorineural hearing loss fitted with a 2-channel linear hearing aid. Subjects rated the speech clarity and quality of average (65 dBA) and loud (80 dBA) speech, in quiet and in noise, with the hearing aid set to a number of OSPL settings. These data were used to evaluate the validity of the Predicted OSPL. Frequency-specific loudness discomfort levels (LDLs) were measured to determine whether use of measured LDLs would improve the accuracy of the prediction. RESULTS: The Predicted Minimum Acceptable OSPL was in good agreement with the measured minimum acceptable OSPL for both the low- and high-frequency channels. The Predicted Maximum Acceptable OSPL was in good agreement with the measured maximum acceptable OSPL for the low-frequency channel, but was only a fair predictor for the high-frequency channel. The use of measured LDLs rather than predicted LDLs did little to improve the accuracy of the fitting. A direct comparison between the NAL single-channel and multichannel prescribed OSPL settings showed that most listeners rated speech clarity higher for the multichannel settings. CONCLUSIONS: In two channel hearing aids, the NAL Predicted Minimum Acceptable OSPL and Predicted Maximum Acceptable OSPL are reasonable predictors of minimum and maximum OSPL levels measured using sound clarity and quality ratings. The results of this study support the use of the NAL prescriptive formula for setting OSPL in multichannel hearing aids. Such settings should be verified by having the listener rate the loudness of an intense speech signal. If tolerance problems are evident, the OSPL in the high-frequency channel(s) should be reduced first.

Acoustic Stimulation↗
PubMed2001

Comparing loudness normalization (IHAFF) with speech intelligibility maximization (NAL-NL1) when implemented in a two-channel device.

OBJECTIVE: At least two rationales are available for fitting wide dynamic range compression hearing aids. The goal of one rationale is to normalize loudness, and the goal of the second rationale is to maximize speech intelligibility. Neither rationale has been validated against other fitting rationales for the range of input levels common to the hearing aid user in the real world. The goal of the study was to compare the two rationales when implemented in a 2-channel compression hearing aid. DESIGN: Loudness normalization and speech intelligibility maximization were implemented using the Independent Hearing Aid Fitting Forum (IHAFF) and the National Acoustic Laboratories' Nonlinear (NAL-NL1) prescriptive formulas. Twenty-four subjects (eight for each of three groups of mild flat, moderate/severe flat, and steeply sloping hearing loss) participated in the study. Each subject completed an initial laboratory test, field test, and final laboratory test. The laboratory test consisted of a paired-comparison judgment for each prescriptive formula using four stimuli under both quiet and noisy listening conditions and a sentence recognition test using Bamford-Kowal-Bench sentences. In the field test, subjects evaluated the two rationales in individually selected everyday listening conditions for 4 wk. A digital simulation of the fitting rationales implemented in two channels was used for laboratory testing and a digital 2-memory, 2-channel device was used for field testing. Subjects adjusted the overall gain of each response to their preferred listening level in both the laboratory and in the field. RESULTS: Data collected in the laboratory before and after the field test showed no indication of significant learning or acclimatization effects. For each stimulus presented in the paired-comparison test more subjects preferred NAL-NL1 than preferred IHAFF. For the sentence recognition test, subjects performed significantly better with NAL-NL1 than IHAFF in a low-frequency weighted background noise. Sixteen out of 22 subjects who completed the field test reported a preference for the NAL-NL1 response. The remaining six subjects preferred IHAFF. The paired-comparison test and field test revealed that while the achieved root-mean-square (rms) difference between fittings for an input level of 65 dB SPL was small, the preference for either rationale was small. As the rms difference between fittings increased, the score in favor of NAL-NL1 increased. The correlation between the differences in satisfaction score obtained in the field test and the rms differences between the responses fitted was statistically significant. CONCLUSIONS: When the two fitting rationales prescribed substantially different responses for a 65 dB SPL input and these differences were achieved in the fitting, then the subjects preferred NAL-NL1. Even when the difference between fittings was small, the subjects preferred and performed better with NAL-NL1 when listening in a low-frequency weighted background noise.

Acoustic Stimulation↗
PubMed2001

The preferred number of channels (one, two, or four) in NAL-NL1 prescribed wide dynamic range compression (WDRC) devices.

OBJECTIVE: The recently introduced NAL-NL1 rationale for fitting WDRC devices prescribes a relatively high compression threshold and prescribes compression ratios lower than those prescribed by loudness normalization rationales. The aim of this study was to investigate whether the compression characteristic prescribed by NAL-NL1 is most effective in a single-channel scheme or in a multi-channel scheme. DESIGN: Twenty-four subjects with flat or steeply sloping hearing loss participated in the study. One, two, and four channels were implemented digitally in the laboratory and evaluated on the basis of a paired-comparison test and a speech recognition test. The test stimuli consisted of speech and noise presented at average input levels, and speech and noise alternating every 3 sec among different input levels. The single-channel and 2-channel NAL-NL1 prescriptions were also evaluated in individually selected everyday situations in the field using a digital 2-memory device. RESULTS: The three compression schemes produced no significant difference in speech recognition scores. Most subjects showed no preference for either scheme in the paired-comparison test. Those who did mainly selected the single-channel scheme. These preferences can be explained on the basis on audibility and quality. In the field all subjects with a steeply sloping loss, but one, preferred the 2-channel scheme. Among the subjects with a flat loss more preferred the single-channel scheme than preferred the 2-channel scheme. Statistical analyses showed that those who preferred the 2-channel scheme were fitted with significantly greater differences in the compression ratio in the high frequencies, and those who preferred the single-channel scheme were fitted with significantly greater differences in the high-frequency gain for a 65 dB input. CONCLUSIONS: Multi-channel compression prescribed according to NAL-NL1 in up to four channels showed no adverse effects on speech recognition relative to a single-channel scheme. The paired-comparison test showed a small, but explainable preference for the single-channel scheme. The field test revealed a preference for the 2-channel scheme by subjects with steeply sloping loss. When using the NAL-NL1 rationale it is recommended to use at

Acoustic Stimulation↗
PubMed2002

Relationship between intensity and reaction time in normal-hearing infants and adults.

OBJECTIVE: Reaction time (RT) to sound is known to be related to loudness in adult listeners. The purpose of this study was to determine whether infants' RT to sound decreases systematically with intensity as it does in adults. DESIGN: RT was measured for 24 6- to 9-mo-old infants and 11 19- to 26-yr-old adults. All participants were normal hearing, naïve listeners. The stimuli consisted of 4000 and 1000 Hz pure tones presented to the right ear through an insert earphone. Stimulus intensities ranged in 10 dB steps from 40 to 80 dB SPL for adults and 50 to 90 dB SPL for infants. Infant responses consisted of a head turn toward a reinforcer whereas adults responded by raising their hand. An additional three adults responded with a head turn. RT was defined as the time between the onset of the tone and an observer's button press indicating that a response had occurred. RT was corrected for the observer's reaction time and averaged over three to five repetitions at each level to obtain the mean reaction time (MRT) for each subject, frequency, and level. RESULTS: MRT decreased with increasing intensity in both infants and adults. An examination of the MRT-intensity functions suggests that the infant functions may be steeper than those of adults, although considerable variability exists between listeners. CONCLUSIONS: RT holds potential as a measure of loudness in infants. Whether differences in the MRT-intensity slopes exist between infants and adults is unclear. Future investigations using methods to reduce the variability of RT measurements are needed to examine potential slope differences further.

Acoustic Impedance Tests↗