Monaural Loudness Research Articles

Toward an Individual Binaural Loudness Model for Hearing Aid Fitting and Development.

The individual loudness perception of a patient plays an important role in hearing aid satisfaction and use in daily life. Hearing aid fitting and development might benefit from individualized loudness models (ILMs), enabling better adaptation of the processing to individual needs. The central question is whether additional parameters are required for ILMs beyond non-linear cochlear gain loss and linear attenuation common to existing loudness models for the hearing impaired (HI). Here, loudness perception in eight normal hearing (NH) and eight HI listeners was measured in conditions ranging from monaural narrowband to binaural broadband, to systematically assess spectral and binaural loudness summation and their interdependence. A binaural summation stage was devised with empirical monaural loudness judgments serving as input. While NH showed binaural inhibition in line with the literature, binaural summation and its inter-subject variability were increased in HI, indicating the necessity for individualized binaural summation. Toward ILMs, a recent monaural loudness model was extended with the suggested binaural stage, and the number and type of additional parameters required to describe and to predict individual loudness were assessed. In addition to one parameter for the individual amount of binaural summation, a bandwidth-dependent monaural parameter was required to successfully account for individual spectral summation.

Discrimination of interaural intensity differences and monaural intensity increments

This study assessed the equivalence of a binaural task (two-interval discrimination of interaural intensity differences, IIDs) and a monaural two-interval increment-discrimination task, in which each interval consisted of two noise bursts of different intensities, with listeners identifying the interval with the larger intensity change. Stimuli were broadband noise, with trial-by-trial feedback provided. An overall level rove between intervals forced listeners to compare the two signals within each interval (across ears in the binaural task and across bursts in the monaural task). Both tasks involved presentation of four signals of different intensities, yielding the same optimal decision statistic. Assuming (1) discrimination of IIDs across intervals amounts to discrimination of lateral position and (2) variability in lateral position increases with IID leads to a prediction of Weber's law. Functions relating threshold IID delta (or monaural increment delta) in dB to the standard IID (or increment) in dB had nearly equal slopes in binaural (0.054) and monaural (0.058) conditions. While the derived binaural decision statistic is based on discrimination of an emergent percept of the stimulus (intracranial position), the similarity of results suggests that monaural increment-discrimination may be based on discrimination of a similarly emergent percept (a loudness step). [Work supported by NIH R01DC00683.]

Bimodal Cochlear Implant Listeners' Ability to Perceive Minimal Audible Angle Differences.

Bilateral inputs should ideally improve sound localization and speech understanding in noise. However, for many bimodal listeners [i.e., individuals using a cochlear implant (CI) with a contralateral hearing aid (HA)], such bilateral benefits are at best, inconsistent. The degree to which clinically available HA and CI devices can function together to preserve interaural time and level differences (ITDs and ILDs, respectively) enough to support the localization of sound sources is a question with important ramifications for speech understanding in complex acoustic environments. To determine if bimodal listeners are sensitive to changes in spatial location in a minimum audible angle (MAA) task. Repeated-measures design. Seven adult bimodal CI users (28-62 years). All listeners reported regular use of digital HA technology in the nonimplanted ear. Seven bimodal listeners were asked to balance the loudness of prerecorded single syllable utterances. The loudness-balanced stimuli were then presented via direct audio inputs of the two devices with an ITD applied. The task of the listener was to determine the perceived difference in processing delay (the interdevice delay [IDD]) between the CI and HA devices. Finally, virtual free-field MAA performance was measured for different spatial locations both with and without inclusion of the IDD correction, which was added with the intent to perceptually synchronize the devices. During the loudness-balancing task, all listeners required increased acoustic input to the HA relative to the CI most comfortable level to achieve equal interaural loudness. During the ITD task, three listeners could perceive changes in intracranial position by distinguishing sounds coming from the left or from the right hemifield; when the CI was delayed by 0.73, 0.67, or 1.7 msec, the signal lateralized from one side to the other. When MAA localization performance was assessed, only three of the seven listeners consistently achieved above-chance performance, even when an IDD correction was included. It is not clear whether the listeners who were able to consistently complete the MAA task did so via binaural comparison or by extracting monaural loudness cues. Four listeners could not perform the MAA task, even though they could have used a monaural loudness cue strategy. These data suggest that sound localization is extremely difficult for most bimodal listeners. This difficulty does not seem to be caused by large loudness imbalances and IDDs. Sound localization is best when performed via a binaural comparison, where frequency-matched inputs convey ITD and ILD information. Although low-frequency acoustic amplification with a HA when combined with a CI may produce an overlapping region of frequency-matched inputs and thus provide an opportunity for binaural comparisons for some bimodal listeners, our study showed that this may not be beneficial or useful for spatial location discrimination tasks. The inability of our listeners to use monaural-level cues to perform the MAA task highlights the difficulty of using a HA and CI together to glean information on the direction of a sound source.

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.

Dissociation of Detection and Discrimination of Pure Tones following Bilateral Lesions of Auditory Cortex

It is well known that damage to the peripheral auditory system causes deficits in tone detection as well as pitch and loudness perception across a wide range of frequencies. However, the extent to which to which the auditory cortex plays a critical role in these basic aspects of spectral processing, especially with regard to speech, music, and environmental sound perception, remains unclear. Recent experiments indicate that primary auditory cortex is necessary for the normally-high perceptual acuity exhibited by humans in pure-tone frequency discrimination. The present study assessed whether the auditory cortex plays a similar role in the intensity domain and contrasted its contribution to sensory versus discriminative aspects of intensity processing. We measured intensity thresholds for pure-tone detection and pure-tone loudness discrimination in a population of healthy adults and a middle-aged man with complete or near-complete lesions of the auditory cortex bilaterally. Detection thresholds in his left and right ears were 16 and 7 dB HL, respectively, within clinically-defined normal limits. In contrast, the intensity threshold for monaural loudness discrimination at 1 kHz was 6.5±2.1 dB in the left ear and 6.5±1.9 dB in the right ear at 40 dB sensation level, well above the means of the control population (left ear: 1.6±0.22 dB; right ear: 1.7±0.19 dB). The results indicate that auditory cortex lowers just-noticeable differences for loudness discrimination by approximately 5 dB but is not necessary for tone detection in quiet. Previous human and Old-world monkey experiments employing lesion-effect, neurophysiology, and neuroimaging methods to investigate the role of auditory cortex in intensity processing are reviewed.

Using functional magnetic resonance imaging to explore the representation of binaural cues in human auditory cortex

Functional magnetic resonance imaging (fMRI) was used to examine representations of interaural differences of level (ILD) and time (ITD) in human auditory cortex (AC). In one experiment, ILD of amplitude-modulated sounds varied parametrically across 12-s blocks, with a single image acquired at the end of each block (i.e., using a “sparse” imaging protocol). In another experiment, ILD or ITD varied parametrically across brief (1-s) presentations, and responses measured from continuosly-acquired images using an “event-related” paradigm. Whole-head echo-planar imaging (~3x3x3 mm resolution) was conducted at 3T (Philips Achieva), with sounds presented via insert earphones (Sensimetrics). Blood-oxygenation-level-dependent (BOLD) signals were analyzed on each individual's cortical surface using FSL, Freesurfer, and MATLAB. In this presentation, results will be discussed in terms of (1) the tuning of BOLD responses to ILD and ITD; (2) the relationship between tuning to ILD and tuning to monaural intensity; (3) ILD-related information as assessed using multi-voxel pattern analysis; (4) adaptation of the BOLD response as a function of trial-to-trial variation in binaural cues; and (5) whether the BOLD responses reflect physical versus perceptual (e.g., perceived location or loudness) aspects of auditory experience. [Supported by NSF DBI-0107567, NIH R03-DC009482-02S1, R01-DC011548, T32-DC005361]

The role of spectral- and temporal-envelope room-acoustic cues in auditory selective attention.

Listeners can attend to one of several simultaneous messages by tracking one speaker’s voice characteristics. Using differences in the location of sounds in a room, we ask how well cues arising from spatial position compete with these characteristics. Listeners decided which of two simultaneous target words belonged in an attended “context” phrase when it was played simultaneously with a different “distracter” context. Talker difference was in competition with position difference, so the response indicates which cue-type the listener was tracking. Spatial position was found to override talker difference in dichotic conditions when the talkers are similar (male). The salience of cues associated with differences in sounds, bearings decreased with distance between listener and sources. These cues are more effective binaurally. However, there appear to be other cues that increase in salience with distance between sounds. This increase is more prominent in diotic conditions, indicating that these cues are largely monaural. Distances between spectra calculated using a gammatone filterbank (with ERB-spaced CFs) of the room’s impulse responses at different locations were computed, and comparison with listeners’ responses suggested some slight monaural loudness cues, but also monaural “timbre” cues arising from the temporal- and spectral-envelope differences in the speech from different locations.

Testing the binaural equal-loudness-ratio hypothesis with hearing-impaired listeners

The primary purpose of the present experiment was to test whether the binaural equal-loudness-ratio hypothesis (i.e., the loudness ratio between monaural and binaural tones presented at the same Sound Pressure Level, SPL, is independent of SPL) holds for hearing-impaired listeners with bilaterally symmetrical hearing losses. The outcome of this experiment provided a theoretical construct for modeling loudness-growth functions. A cross-modality matching task between string length and tones was used to measure three loudness functions for eight listeners: two monaural (left and right) and one binaural. A multiple linear regression was performed to test the significance of presentation mode (monaural vs binaural and left vs right), level, and their interaction. Results indicate that monaural loudness functions differ between the ears of two listeners. The interaction between presentation mode (binaural/monaural) and level was significant for one listener. Although significant, these differences were quite small. Generally, the binaural equal-loudness-ratio hypothesis appears to hold for hearing-impaired listeners. These data also indicate that loudness-growth functions in two ears of an individual are more similar than loudness-growth functions in ears from different listeners. Finally, it is demonstrated that loudness-growth functions can be constructed for individual listeners from binaural level difference for equal-loudness data.

A test of the Binaural Equal-Loudness-Ratio hypothesis for tones

It is well known that a tone presented binaurally is louder than the same tone presented monaurally. It is less clear how this loudness ratio changes as a function of level. The present experiment was designed to directly test the Binaural Equal-Loudness-Ratio hypothesis (BELRH), which states that the loudness ratio between equal-SPL monaural and binaural tones is independent of SPL. If true, the BELRH implies that monaural and binaural loudness functions are parallel when plotted on a log scale. Cross-modality matches between string length and loudness were used to directly measure binaural and monaural loudness functions for nine normal listeners. Stimuli were 1-kHz 200-ms tones ranging in level from 5 dB SL to 100 dB SPL. A two-way ANOVA showed significant effects of level and mode (binaural or monaural) on loudness, but no interaction between the level and mode. Consequently, no significant variations were found in the binaural-to-monaural loudness ratio across the range of levels tested. This finding supports the BELRH. In addition, the present data were found to closely match loudness functions derived from binaural level differences for equal loudness using the model proposed by Whilby et al. [J. Acoust. Soc. Am. 119, 3931-3939 (2006)].

Directional loudness in an anechoic sound field, head-related transfer functions, and binaural summation

The effect of sound incidence angle on loudness was investigated using real sound sources positioned in an anechoic chamber. Eight normal-hearing listeners produced loudness matches between a frontal reference location and seven sources placed at other directions, both in the horizontal and median planes. Matches were obtained via a two-interval, adaptive forced-choice (2AFC) procedure for three center frequencies (0.4, 1, and 5 kHz) and two overall levels (45 and 65 dB SPL). The results showed that loudness is not constant over sound incidence angles, with directional sensitivity varying over a range of up to 10 dB, exhibiting considerable frequency dependence, but only minor effects of overall level. The pattern of results varied substantially between subjects, but was largely accounted for by variations in individual head-related transfer functions. Modeling of binaural loudness based on the at-ear signals favored a sound-power summation model, according to which the maximum binaural gain is only 3 dB, over competing models based on larger gains, or on the summation of monaural loudness indices.

Empirical evaluation of a model of global psychophysical judgments: III. A form for the psychophysical function and intensity filtering

In part I, a concept of ratio estimation is defined and it is shown that if such estimates depend only upon the physical ratio of the signal to the reference signal, the psychophysical function must be a power function. Assuming the same exponents for each component, an invariance condition, equivalent to a sum of power functions, is studied empirically for binaural loudness. It is fully or partially sustained for 19 of 22 respondents. Since failures may be attributable to different exponents in the two ears, the ratio of the two exponents is estimated but that fails to explain the failures. Other possible explanations are suggested. In part II, an intensity filtering model is presented, accounting for the phenomenon where monaural loudness matches show a bias depending on the matching ear. We show (a) that the existence of such a bias does not alter the prior experimental results; and (b) assuming the power function, that five respondents attenuate the opposite ear and two enhance it.

Speech perception from monaural and binaural information

Two experiments explored the concept of the binaural spectrogram [Culling and Colburn, J. Acoust. Soc. Am. 107, 517-527 (2000)] and its relationship to monaurally derived information. In each experiment, speech was added to noise at an adverse signal-to-noise ratio in the NoS pi binaural configuration. The resulting monaural and binaural cues were analyzed within an array of spectro-temporal bins and then these cues were resynthesized by modulating the intensity and/or interaural correlation of freshly generated noise. Experiment 1 measured the intelligibility of the resynthesized stimuli and compared them with the original NoSo and NoS pi stimuli at a fixed signal-to-noise ratio. While NoS pi stimuli were approximately equal to 50% intelligible, each cue in isolation produced similar (very low) intelligibility to the NoSo condition. The resynthesized combination produced approximately equal to 25% intelligibility. Modulation of interaural correlation below 1.2 kHz and of amplitude above 1.2 kHz was not as effective as their combination across all frequencies. Experiment 2 measured three-point psychometric functions in which the signal-to-noise ratio of the original NoS pi stimulus was increased in 3-dB steps from the level used in experiment 1. Modulation of interaural correlation alone proved to have a flat psychometric function. The functions for NoS pi and for combined monaural and binaural cues appeared similar in slope, but shifted horizontally. The results indicate that for sentence materials, neither fluctuations in interaural correlation nor in monaural intensity are sufficient to support speech recognition at signal-to-noise ratios where 50% intelligibility is achieved in the NoS pi configuration; listeners appear to synergistically combine monaural and binaural information in this task, to some extent within the same frequency region.

Detection and discrimination of monaural and binaural increments and decrements of intensity with a temporal fringe

Detection thresholds are larger for brief, monaural intensity increments in long-duration stimuli than for decrements. This experiment assessed the contribution of a decrement in one ear to direction discrimination of an interaural intensity difference (IID), where a brief intensity increment was presented at one ear and an equal-magnitude intensity decrement at the other. In two-interval monaural tasks, thresholds were measured for detection of an increment, a decrement, and discrimination of the two. In single-interval binaural tasks, thresholds were measured for identifying ear of presentation of an increment, a decrement, and for identification of direction of IID achieved by presenting an increment and decrement to opposite ears. In all cases, thresholds were measured for a 5-ms probe segment as a function of its temporal position in a 50-ms stimulus (broadband noise). The major results: (1) Thresholds for discriminating the ear of presentation of a decrement were much larger than those for simply detecting the decrement monaurally; (2) Interaural thresholds were slightly better when both increment and decrement were present relative to increment alone. These results indicate that the decrements contributed to binaural discrimination, although by themselves the same decrements were detectable but, at best, weakly lateralizable. [Work supported by NIDCD DC00683.]

Monaural and interaural intensity discrimination: level effects and the "binaural advantage".

This study examined whether the level effects seen in monaural intensity discrimination (Weber's law and the "near miss") in a two-interval task are also observed in discrimination of interaural intensity differences (IIDs) in a single-interval task. Both tasks were performed for various standard levels of 4-kHz pure tones and broadband noise. The Weber functions (10 log deltaI/I versus I in dB) in the monaural and binaural conditions were parallel. For noise, the Weber functions had slopes close to zero (Weber's law) while the Weber functions for the tones had a mean slope of -0.089 (near miss). The near miss for the monaural and binaural tasks with tones was eliminated when a high-pass masker was gated with the listening intervals. The near-miss was also observed for 250- and 1000-Hz tones in the binaural task despite overall decreased sensitivity to changes in IID at 1000 Hz. The binaural thresholds showed a small (about 2-dB) advantage over monaural thresholds only in the broadband noise conditions. More important, however, is the fact that the level effects seen monaurally are also seen binaurally. This suggests that the basic mechanisms responsible for Weber's law and the near miss are common to monaural and binaural processing.

Level effects in monaural and interaural intensity discrimination

Discrimination of interaural level differences (ILDs) is often assessed using a two-interval task in which ILD changes between intervals. In such a situation, overall level is usually roved in order to minimize monaural cues. This roving makes it difficult to assess level-dependent effects. In the present experiment, monaural intensity discrimination in a 2IFC task was compared to ILD discrimination in a single-interval task, thus producing an analogous situation in terms of number of ‘‘observations’’ and eliminating the need for an overall level rove. Monaural intensity DLs and ILD discrimination thresholds were measured as a function of level for 4-kHz tones and for broadband noise. The Weber functions (10<th>logΔI/I vs I in dB) in the monaural and binaural conditions were parallel. For the noise the Weber functions had slopes close to zero (Weber’s law); for the tones the slopes were −0.082 (near-miss to Weber’s law). Overall, the binaural thresholds showed a small, approximately 2 dB, advantage over the monaural thresholds. The important aspect, however, is that the level effects seen monaurally are also seen binaurally. This suggests that the basic processes responsible for Weber’s law and the near-miss occur prior to binaural interaction. [Work supported by NIDCD DC05343 and DC00683.]

Monaural Loudness Adaptation for Middle-Intensity Middle-Frequency Signals: The Importance of Measurement Technique

Using the Simple Adaptation technique (SA) and the Ipsilateral Comparison Paradigm (ICP), the authors studied monaural loudness adaptation to a middle-intensity [60 dB(A)] tone at signal frequencies of 250, 1000, and 4000 Hz in the left and right ears. Adaptation effects were absent when the SA procedure was used. However, they were observed uniformly across all frequency values with the ICP, a result that challenges the assertion in the literature, on the basis of SA measures, that loudness adaptation for middle-intensity signals occurs only at frequencies above 4000 Hz. The ICP features periodic intensity modulations (±10 dB relative to the base signal) to accommodate listeners' needs for referents by which they can gauge subtle changes in the loudness of the adapting tone, a key component that is missing in the SA method. Adaptation effects in this investigation were similar in both ears, supporting the equal susceptibility assumption common in loudness adaptation studies.

Derivation of intensity-discrimination functions from loudness functions

Intensity-discrimination functions are computed from their concomitant loudness functions in a procedure where the only adjustable parameter sets the scale to match the measured intensity-discrimination data. The equation connecting loudness to intensity discrimination is determined from monaural loudness- and intensity-discrimination measurements at 1 kHz. Predictions of intensity-discrimination functions are then computed for a low-frequency tone masked by an adjacent high-pass noise, for broadband noise, and for high-frequency tones at 12.5 and 16 kHz. Results show that the derived intensity-discrimination functions closely capture the overall shape of the experimental data. A U-shaped function is obtained for the partially masked low-frequency tone, whereas a function approximating Weber’s law is observed for broadband noise and also at 16 kHz. The good agreement between the calculated and measured functions implies that the form of the intensity-discrimination functions is strongly dependent on local variations in shape of the loudness functions. Together, these results provide further evidence to support the notion of an intimate relation between loudness and intensity discrimination. [Work supported in part by NEDO, Japan.]

Ipsilateral Loudness Adaptation Over Multiple Intensity Levels

Could monaural loudness adaptation be a simple artifact of psychophysical contrast? From adaptation data based on the Ipsilateral Comparison Paradigm (ICP), A. J. Dange, J. S. Warm, E. M. Weiler, and W. N. Dember (1993) concluded that loudness adaptation was not an artifact of psychophysical contrast, but their conclusion was dependent on results from one intensity. This study, involving multiple intensities, re-examined the issue of contrast versus adaptation and generally supported the conclusions of Dange et al. The results also showed an unexpected asymmetry of adaptation based on the direction of the referent modulation used with the ICP technique. Some implications are discussed.

Effects of Reference Interaural Time and Intensity Differences on Binaural Performance in Listeners with Normal and Impaired Hearing

The purpose of this research was to measure the effects of reference interaural time and intensity differences on binaural performance in listeners with normal hearing and impaired hearing for a number of different binaural tests. Experiment 1 measures the dependence of binaural detection and discrimination performance on reference interaural intensity differences (IID) in the range of +/- 12 dB for listeners with normal hearing. Experiment 2 extends these measures to include reference IIDs and interaural time differences (ITD) for two groups of listeners with normal hearing with offsets in the range of +/- 12 dB and +/- 300 microseconds (group 1) and +/-24 dB and +/- 600 microseconds (group 2). Experiment 3 includes the same tests and conditions as experiment 2 for listeners with various hearing impairments. A set of psychophysical measurements was completed on 11 listeners with sensorineural hearing losses and 9 listeners with clinically normal hearing. The primary measurements were a set of four binaural detection and interaural discrimination thresholds measured for two 1/3-octave bands of Gaussian noise, one centered at 500 Hz and the other at 4000 Hz. Specifically, we measured binaural (antiphasic) detection thresholds for tones centered in the masking noise as well as the just-noticeable differences (JNDs) in IID, ITD, and interaural cross-correlation (ICC) for each of the noise-band stimuli. All measurements were done for a number of combinations of reference IID and ITD. In addition to these primary measurements, several other measurements were made on each subject, including monaural absolute thresholds, monaural intensity discrimination, monaural masked thresholds, and intensity levels required for interaurally balanced loudness and for a centered image. All measurements were made using a relatively quick, adaptive procedure. For the subjects with normal hearing, measured dependencies of the IID and ITD JNDs using noise stimuli on reference ITD and IID are different from those previously reported for tonal stimuli. Binaural performance of the listeners with impaired hearing varies widely across subjects and tests and is generally poorer than that of listeners with normal hearing. On the basis of the results for subjects with hearing impairments, we have reached several conclusions. First, the results for the binaural measurements cannot be explained in terms of available monaural audiometric and psychophysical measurements on these subjects. Second, the subjects' binaural abilities show no significant improvement with any combinations in the reference values of ITD and IID, providing negative evidence for the hypothesis that degraded performance for some subjects may be due to internal interaural offsets in ITD or IID. Third, the hypothesis that binaural detection and ICC discrimination are related, suggested by Durlach et al (1986), is generally supported. Fourth, binaural detection performance is not simply explained in terms of sensitivities to ITD and IID.

Fletcher and loudness

In this presentation, some of the pioneering work performed by Harvey Fletcher and colleagues on the loudness of simple and complex sounds will be reviewed. The focus will be placed on the model and data presented by Fletcher and Munson [H. Fletcher and W. A. Munson, J. Acoust. Soc. Am. 5, 82–108 (1933)]. In this classic paper, the authors lay a solid foundation for the understanding of loudness which remains remarkably intact today in light of contemporary psychophysical and physiological knowledge. They provide thorough descriptions of several loudness phenomena, including loudness growth, monaural loudness additivity, and binaural loudness summation. Among other things, they demonstrate that loudness for a single tone grows as a function of the cube root of stimulus intensity, that loudness is additive for stimulus components in separate auditory filters or in separate ears, and that loudness of partially masked stimulus components is also additive once adjustments for partial masking have been made. F...