Intelligibility and detectability of speech measured diotically and dichotically in groups of listeners with, at most, "slight" hearing loss.

The purpose of this investigation was to determine if a group of listeners having thresholds at 4 kHz exceeding 7.5 dB HL, and no more than "slight" hearing loss, would exhibit degradations in performance when "target" stimuli were masked tokens of speech. Intelligibility thresholds and detection thresholds were measured separately for speech masked by flat-spectrum noise or speech-shaped noise. Both NoSo and NoSπ configurations were employed. Consistent with findings of earlier investigations, when maskers and speech tokens were broadband, NoSo and NoSπ detection thresholds were substantially lower than intelligibility thresholds. More importantly, for the small cohorts tested, mean thresholds obtained from the ≤7.5 dB and >7.5 dB groups were equivalent. When maskers and speech targets were high-pass filtered at 500 Hz and above, the mean intelligibility thresholds obtained from the >7.5 dB group were about 4 dB higher than those obtained from the ≤7.5 dB group, independent of masker type and interaural configuration of the stimuli. In real-world listening situations, such deficits may manifest themselves as substantially reduced speech intelligibility and, perhaps, increased "listening effort" for listeners whose thresholds at 4 kHz exceed 7.5 dB HL and who have no more than "slight" hearing loss.

A crew of listeners with no more than "slight" hearing loss who exhibit binaural deficits also exhibit reduced amounts of binaural interference.

Listeners having, at most, "slight" hearing loss, specifically those having absolute thresholds at 4 kHz exceeding 7.5 dB HL, have been shown to exhibit deficits in binaural detection that appear to stem from increased levels of stimulus-dependent, additive internal noise [Bernstein and Trahiotis (2016). J. Acoust. Soc. Am. 140, 3540-3548; Bernstein and Trahiotis (2018). J. Acoust. Soc. Am. 144, 292-307]. This study assessed whether such listeners exhibit greater susceptibility to "binaural interference." NoSo and NoSπ tone-in-noise detection thresholds were measured for stimuli centered at 4 kHz in the absence of any interfering stimuli and in the presence of simultaneously gated diotic or interaurally uncorrelated noise centered at 500 Hz. Results indicated that listeners exhibiting elevated NoSπ thresholds (typical of those in ">7.5 dB groups"), actually exhibit less binaural interference than do those exhibiting lower NoSπ thresholds typical of those in "≤7.5 dB HL" groups. That outcome cannot be explained by a "ceiling effect" stemming from interferer-induced loss of the ability to utilize binaural cues to detect the signal. The relatively smaller amounts of binaural interference exhibited by listeners with relatively elevated NoSπ thresholds notwithstanding, it is argued that the interference they do exhibit may place them at a distinct disadvantage in everyday listening environments.

A crew of listeners with no more than "slight" hearing loss who exhibit binaural deficits also exhibit higher levels of stimulus-independent internal noise.

Listeners having, at most, "slight" hearing loss may exhibit deficits in binaural detection which appear to stem from increased levels of stimulus-dependent, additive internal noise [Bernstein and Trahiotis, J. Acoust. Soc. Am. 140, 3540-3548 (2016); J. Acoust. Soc. Am. 144, 292-307 (2018)]. This study reports that a small crew of such listeners also exhibits increased levels of low-level, stimulus-independent, additive internal noise. Detection thresholds were measured in: (1) the NoSπ configuration as a function of masker level; (2) the NρSπ configuration as a function of masker interaural correlation (ρ); (3) "the quiet" for So and Sπ tonal signals. Those measures were combined suitably to yield estimates of stimulus-independent, additive internal noise, separately, at center frequencies of 250, 500, and 4000 Hz. Derived levels of internal noise were found to be elevated, by about 5 dB at 250 and 500 Hz, and by about 9 dB at 4 kHz, for the group of listeners having no more than slight hearing loss and who exhibited deficits in binaural detection. The new findings, taken together with earlier investigations by the authors (which included data obtained from dozens of listeners), provide evidence that such listeners have greater levels of both stimulus-dependent and stimulus-independent, additive internal noise.

Binaural detection as a joint function of masker bandwidth, masker interaural correlation, and interaural time delay: Empirical data and modeling.

Empirical data are reported demonstrating how binaural detection is affected by joint variation of masker bandwidth, masker interaural correlation, and interaural time delay (ITD) of both masker and tonal signal. Most of the data were obtained with stimuli centered at 500 Hz; supplemental measures were obtained with stimuli centered at 4 kHz. The results indicate that as the interaural correlation of the masker (ρ) is decreased there is (1) an overall increase in threshold signal-to-noise ratio (S/N) and (2) a progressively smaller effect on threshold S/N as ITD is increased. All of the data were accounted for quite accurately using the same quantitative, interaural cross-correlation-based model that was recently shown to account for binaural detection and discrimination data obtained in previous experiments. Importantly, the new data were predicted and explained using values of model parameters that were identical or very close to those found to predict accurately the earlier data. The success of the enterprise attests to the robustness of the approach and the generality of the model's ability to make accurate predictions of binaural performance over a wide range of historically important stimulus conditions.

No more than "slight" hearing loss and degradations in binaural processing.

Listeners having, at most, "slight" hearing loss may exhibit substantial deficits in binaural detection [Bernstein and Trahiotis. (2016). J. Acoust. Soc. Am. 140, 3540-3548; (2018). J. Acoust. Soc. Am. 144, 292-307]. This study assessed whether such listeners also exhibit deficits discriminating interaural temporal disparities (ITDs) or interaural intensitive disparities (IIDs) and whether any deficits observed in those discrimination tasks would be accounted for by the interaural cross-correlation based model that successfully accounts for binaural detection. Thresholds were measured for detection of tones masked by noise in the NoSπ configuration and discrimination of ITD or IID. Gaussian noises (100 Hz-wide), served as maskers in the detection task and as reference and target stimuli in the discrimination tasks. Stimuli were centered at 500 Hz or 4 kHz. The latter were transpositions of stimuli centered at 125 Hz. Results demonstrate that listeners having, at most, slight hearing loss and who exhibit deficits in binaural detection, also exhibit deficits in ITD- and IID-discrimination. Coupled with appropriate decision variables, the cross-correlation-based model that accounts for elevated binaural detection thresholds among such listeners also accounted for their elevated ITD- and IID-thresholds. The deficits in all three tasks appear to stem from increased levels of stimulus-dependent, additive internal noise.

Effects of interaural delay, center frequency, and no more than "slight" hearing loss on precision of binaural processing: Empirical data and quantitative modeling.

This study assessed how precision of binaural processing is affected by center frequency (CF), interaural temporal disparity (ITD), and listeners' hearing status. Tonal signals and 100-Hz-wide Gaussian noise maskers were employed at CFs ranging between 250 and 8000 Hz, in octave steps. In addition, for CFs of 2000, 4000, and 8000 Hz, transposed maskers and signals were employed. All listeners had no greater than "slight" hearing losses (i.e., no thresholds greater than 25 dB HL). Across all CFs and ITDs tested, binaural detection thresholds were elevated for listeners whose absolute thresholds at 4 kHz exceeded 7.5 dB HL. That outcome is consistent with results from Bernstein and Trahiotis [(2016). J. Acoust. Soc. Am. 140, 3540-3548]. Quantitative predictions of binaural detection thresholds derived via a comprehensive interaural correlation-based model of binaural processing were highly accurate across the entire set of data. The modeling results suggest that elevated thresholds from listeners having small hearing losses stem from elevated levels of stimulus-dependent, additive internal noise. They do not appear to stem from increased levels of noise within the central binaural comparator or from reduced sensitivity to changes in interaural correlation produced by the addition of the signal to the masker.

An interaural-correlation-based approach that accounts for a wide variety of binaural detection data.

Interaural cross-correlation-based models of binaural processing have accounted successfully for a wide variety of binaural phenomena, including binaural detection, binaural discrimination, and measures of extents of laterality based on interaural temporal disparities, interaural intensitive disparities, and their combination. This report focuses on quantitative accounts of data obtained from binaural detection experiments published over five decades. Particular emphasis is placed on stimulus contexts for which commonly used correlation-based approaches fail to provide adequate explanations of the data. One such context concerns binaural detection of signals masked by certain noises that are narrow-band and/or interaurally partially correlated. It is shown that a cross-correlation-based model that includes stages of peripheral auditory processing can, when coupled with an appropriate decision variable, account well for a wide variety of classic and recently published binaural detection data including those that have, heretofore, proven to be problematic.

Behavioral manifestations of audiometrically-defined "slight" or "hidden" hearing loss revealed by measures of binaural detection.

This study assessed whether audiometrically-defined "slight" or "hidden" hearing losses might be associated with degradations in binaural processing as measured in binaural detection experiments employing interaurally delayed signals and maskers. Thirty-one listeners participated, all having no greater than slight hearing losses (i.e., no thresholds greater than 25 dB HL). Across the 31 listeners and consistent with the findings of Bernstein and Trahiotis [(2015). J. Acoust. Soc. Am. 138, EL474-EL479] binaural detection thresholds at 500 Hz and 4 kHz increased with increasing magnitude of interaural delay, suggesting a loss of precision of coding with magnitude of interaural delay. Binaural detection thresholds were consistently found to be elevated for listeners whose absolute thresholds at 4 kHz exceeded 7.5 dB HL. No such elevations were observed in conditions having no binaural cues available to aid detection (i.e., "monaural" conditions). Partitioning and analyses of the data revealed that those elevated thresholds (1) were more attributable to hearing level than to age and (2) result from increased levels of internal noise. The data suggest that listeners whose high-frequency monaural hearing status would be classified audiometrically as being normal or "slight loss" may exhibit substantial and perceptually meaningful losses of binaural processing.

Converging measures of binaural detection yield estimates of precision of coding of interaural temporal disparities.

This presentation reports binaural detection data obtained using a special set of three stimulus configurations. The configurations are shown to yield "converging" measures that allow one to describe how precision of coding of interaural temporal disparities (ITDs) changes as a function of both reference ITD and the center frequency of the stimuli.

Sensitivity to envelope-based interaural delays at high frequencies: center frequency affects the envelope rate-limitation.

Sensitivity to ongoing interaural temporal disparities (ITDs) was measured using bandpass-filtered pulse trains centered at 4600, 6500, or 9200 Hz. Save for minor differences in the exact center frequencies, those target stimuli were those employed by Majdak and Laback [J. Acoust. Soc. Am. 125, 3903-3913 (2009)]. At each center frequency, threshold ITD was measured for pulse repetition rates ranging from 64 to 609 Hz. The results and quantitative predictions by a cross-correlation-based model indicated that (1) at most pulse repetition rates, threshold ITD increased with center frequency, (2) the cutoff frequency of the putative envelope low-pass filter that determines sensitivity to ITD at high envelope rates appears to be inversely related to center frequency, and (3) both outcomes were accounted for by assuming that, independent of the center frequency, the listeners' decision variable was a constant criterion change in interaural correlation of the stimuli as processed internally. The finding of an inverse relation between center frequency and the envelope rate limitation, while consistent with much prior literature, runs counter to the conclusion reached by Majdak and Laback.

Accounting for binaural detection as a function of masker interaural correlation: effects of center frequency and bandwidth.

Binaural detection was measured as a function of the center frequency, bandwidth, and interaural correlation of masking noise. Thresholds were obtained for 500-Hz or 125-Hz Sπ tonal signals and for the latter stimuli (noise or signal-plus-noise) transposed to 4 kHz. A primary goal was assessment of the generality of van der Heijden and Trahiotis' [J. Acoust. Soc. Am. 101, 1019-1022 (1997)] hypothesis that thresholds could be accounted for by the "additive" masking effects of the underlying No and Nπ components of a masker having an interaural correlation of ρ. Results indicated that (1) the overall patterning of the data depended neither upon center frequency nor whether information was conveyed via the waveform or by its envelope; (2) thresholds for transposed stimuli improved relative to their low-frequency counterparts as bandwidth of the masker was increased; (3) the additivity approach accounted well for the data across stimulus conditions but consistently overestimated MLDs, especially for narrowband maskers; (4) a quantitative approach explicitly taking into account the distributions of time-varying ITD-based lateral positions produced by masker-alone and signal-plus-masker waveforms proved more successful, albeit while employing a larger set of assumptions, parameters, and computational complexity.

Binaural interference: effects of temporal interferer fringe and interstimulus interval.

Binaural interference refers to the phenomenon in which the potency of binaural cues conveyed by a "target" stimulus occupying one spectral region is degraded by the presence of an "interferer" stimulus occupying a spectral region remote from the target. It is typified by conditions in which thresholds for detection of interaural temporal difference conveyed by a high-frequency target are elevated when the target is accompanied by a spectrally remote low-frequency interferer. This study explored effects of temporal relations between targets and interferers on binaural interference. In the first experiment, duration by which the interferer preceded and/or trailed the target (onset and offset "fringes") was varied. Results indicated binaural interference decreased with total duration of the temporal fringe, but did not depend on whether that duration was composed of onset, offset, or onset + offset fringes. In the second experiment, binaural interference was measured as a function of the interstimulus interval (ISI) between the two presentations of the target. Results indicated that shorter ISIs increased thresholds in both the interferer and no-interferer conditions, but did not affect binaural interference. These results suggest that the mechanisms underlying the effects of manipulations of the interferer temporal fringe and manipulation of the ISI are essentially independent.

When and how envelope "rate-limitations" affect processing of interaural temporal disparities conveyed by high-frequency stimuli.

The purpose of this chapter is to bring together historical and current findings that reveal the presence, influence, and operation of a type of envelope "rate-limitation." The rate-limitation has been revealed in both monaural and binaural experiments. Specifically, there appears to be a low-pass envelope-filtering process that (1) functionally attenuates fluctuations of the envelope above about 150 Hz and (2) is not attributable to peripheral band-pass filtering. We show a variety of empirical outcomes and theoretical analyses that converge to demonstrate and to describe how this type of filtering constrains the processing of interaural temporal disparities (ITDs) conveyed by the envelopes of high-frequency stimuli in experiments concerning binaural detection. Included are recent behavioral and neurophysiological findings regarding how such filtering may vary with the center frequency of the stimulus.

The effect of overall level on sensitivity to interaural differences of time and level at high frequencies.

For high-frequency complex stimuli, detection thresholds for envelope-based interaural time differences (ITDs) decrease with overall level. Substantial heterogeneity is, however, evident among the findings concerning the rate at which thresholds decline with level. This study investigated factors affecting the influence of overall level on threshold ITDs. Thresholds were measured as a function of overall level for 4-kHz-centered "targets" in three experiments focusing, respectively, on stimulus-type (sinusoidally amplitude-modulated or "transposed" tones), modulation frequency, and details concerning low-pass noise used to mask low-frequency distortion products. Results indicated that (1) log-ITD thresholds decreased linearly with overall level; (2) slopes relating log-ITD thresholds to level did not depend significantly on stimulus type; (3) lower modulation frequencies produced greater dependencies of thresholds on overall level than did higher modulation frequencies; (4) the effect of overall level on threshold-ITDs was independent of the interaural configuration and levels of the low-pass noise maskers tested; (5) synchronously gating the low-pass noise and target produced a greater dependency of thresholds on the overall level of the target than did continuous or temporally "fringed" presentation of the noise. A fourth experiment showed that threshold interaural level differences were somewhat less affected by changes in overall level than were threshold ITDs.

Lateralization produced by interaural temporal and intensitive disparities of high-frequency, raised-sine stimuli: data and modeling.

An acoustic pointing task was used to measure extents of laterality produced by combinations of ongoing envelope-based interaural temporal disparities (ITDs) and interaural intensitive disparities (IIDs) of 4-kHz-centered raised-sine stimuli [Bernstein and Trahiotis, J. Acoust. Soc. Am. 125, 3234-3242 (2009),] while varying, parametrically, their peakedness, depth of modulation, and frequency of modulation. The study was designed to assess whether IIDs act as "weights" within the putative "binaural display" at high spectral frequencies (where the envelopes convey ITD-information) as appears to be the case at low spectral frequencies (where the waveforms, i.e., fine-structure and envelopes, convey ITD-information). The data indicate that envelope-based IIDs do principally act as weights and that they appear to exert their influence on lateral position independently of the influence of ITDs. Quantitative analyses revealed that an augmented form of the cross-correlation-based "position-variable" model of Stern and Shear [J. Acoust. Soc. Am. 100, 2278-2288 (1996)] accounted for 94% of the variance in the data. This success notwithstanding, for a small subset of the data, predictions could be improved by assuming that the listeners utilized information within auditory filters having center frequencies above 4 kHz.

Lateralization produced by envelope-based interaural temporal disparities of high-frequency, raised-sine stimuli: empirical data and modeling.

An acoustic pointing task was used to measure extents of laterality produced by ongoing interaural temporal disparities (ITDs) conveyed by the envelopes of 4-kHz-centered raised-sine stimuli while varying, parametrically, their peakedness, depth of modulation, and frequency of modulation. One purpose of the study was to determine whether such manipulations would produce changes in laterality logically consistent with those found for ITD-discrimination thresholds reported by Bernstein and Trahiotis [J. Acoust. Soc. Am. 125, 3234-3242 (2009)]. The data obtained revealed that they did in that (1) increasing depth of modulation, peakedness, or frequency of modulation between 32 and 128 Hz produced smaller threshold ITDs and greater laterality and (2) increasing frequency of modulation to 256 Hz produced modest increases in threshold ITDs and modest decreases in laterality. The extents of laterality measured were successfully accounted for via an augmentation of the cross-correlation-based "position-variable" modeling approach developed by Stern and Shear [J. Acoust. Soc. Am. 100, 2278-2288 (1996)] to account for ITD-based extents of laterality obtained at low spectral frequencies.

Lateralization produced by interaural intensitive disparities appears to be larger for high- vs low-frequency stimuli.

The purpose of this communication is to report the results of a study indicating that a given magnitude of interaural intensitive disparity (IID) produced a larger extent of laterality, as measured via an acoustic pointer, for stimuli centered at 4 kHz than for stimuli centered at 500 Hz. The data and their analysis, taken together, suggest that the findings reflect true across-frequency differences rather than being manifestations of response-related factors.

Accounting quantitatively for sensitivity to envelope-based interaural temporal disparities at high frequencies.

Bernstein and Trahiotis [(2009). J. Acoust. Soc. Am. 125, 3234-3242] reported threshold interaural temporal disparities (ITDs) conveyed by the envelopes of 4-kHz-centered "raised-sine" stimuli. A raised-sine stimulus consists of a carrier modulated by a sinusoid raised to an exponent. Such stimuli permitted Bernstein and Trahiotis to vary, independently, stimulus modulation frequency, modulation depth, and "relative peakedness/deadtime." An interaural correlation-based model that included stages mimicking peripheral auditory processing captured most of the data save for an overestimation of threshold ITDs obtained when the depth of modulation was 25% and the raised-sine exponent was 8.0. The purpose of the present study was: (1) to present a quantitative evaluation of how well other measures, including normalized envelope fourth moment, envelope peakwidth, and envelope "deadtime" might also account for the data reported by Bernstein and Trahiotis and (2) to present new threshold ITDs measured while varying, factorially, depth of modulation, raised-sine exponent, and modulation frequency. Quantitative analyses of both the prior and the new data showed that the normalized interaural correlation, computed subsequent to peripheral auditory processing, provided the most accurate predictions. Importantly, the overestimation of threshold ITDs did not occur when it was assumed that listeners can employ information within "off-frequency" auditory filters.