Monaural Pitch Research Articles

Altered binaural hearing in pre-ataxic and ataxic mutation carriers of spinocerebellar ataxia type 3

Brainstem degeneration is a prominent feature of spinocerebellar ataxia type 3 (SCA3), involving structures that execute binaural synchronization with microsecond precision. As a consequence, auditory processing may deteriorate during the course of disease. We tested whether the binaural “Huggins pitch” effect is suitable to study the temporal precision of brainstem functioning in SCA3 mutation carriers. We expected that they would have difficulties perceiving Huggins pitch at high frequencies, and that they would show attenuated neuromagnetic responses to Huggins pitch. The upper limit of Huggins pitch perception was psychoacoustically determined in 18 pre-ataxic and ataxic SCA3 mutation carriers and in 18 age-matched healthy controls. Moreover, the cortical N100 response following Huggins pitch onset was acquired by means of magnetoencephalography (MEG). MEG recordings were analyzed using dipole source modeling and comprised a monaural pitch condition and a no-pitch condition with simple binaural correlation changes. Compared with age-matched controls, ataxic but not pre-ataxic SCA3 mutation carriers had significantly lower frequency limits up to which Huggins pitch could be heard. Listeners with lower frequency limits also showed diminished MEG responses to Huggins pitch, but not in the two control conditions. Huggins pitch is a promising tool to assess brainstem functioning in ataxic SCA3 patients. Future studies should refine the psychophysiological setup to capture possible performance decrements also in pre-ataxic mutation carriers. Longitudinal observations will be needed to prove the potential of the assessment of Huggins pitch as a biomarker to track brainstem functioning during the disease course in SCA3.

An Alternative Explanation for Difficulties with Speech in Background Talkers: Abnormal Fusion of Vowels Across Fundamental Frequency and Ears.

Normal-hearing (NH) listeners use frequency cues, such as fundamental frequency (voice pitch), to segregate sounds into discrete auditory streams. However, many hearing-impaired (HI) individuals have abnormally broad binaural pitch fusion which leads to fusion and averaging of the original monaural pitches into the same stream instead of segregating the two streams (Oh and Reiss, 2017) and may similarly lead to fusion and averaging of speech streams across ears. In this study, using dichotic speech stimuli, we examined the relationship between speech fusion and vowel identification. Dichotic vowel perception was measured in NH and HI listeners, with across-ear fundamental frequency differences varied. Synthetic vowels /i/, /u/, /a/, and /ae/ were generated with three fundamental frequencies (F0) of 106.9, 151.2, and 201.8Hz and presented dichotically through headphones. For HI listeners, stimuli were shaped according to NAL-NL2 prescriptive targets. Although the dichotic vowels presented were always different across ears, listeners were not informed that there were no single vowel trials and could identify one vowel or two different vowels on each trial. When there was no F0 difference between the ears, both NH and HI listeners were more likely to fuse the vowels and identify only one vowel. As ΔF0 increased, NH listeners increased the percentage of two-vowel responses, but HI listeners were more likely to continue to fuse vowels even with large ΔF0. Binaural tone fusion range was significantly correlated with vowel fusion rates in both NH and HI listeners. Confusion patterns with dichotic vowels differed from those seen with concurrent monaural vowels, suggesting different mechanisms behind the errors. Together, the findings suggest that broad fusion leads to spectral blending across ears, even for different ΔF0, and may hinder the stream segregation and understanding of speech in the presence of competing talkers.

Binaural Pitch Fusion: Binaural Pitch Averaging in Cochlear Implant Users With Broad Binaural Fusion.

Individuals who use hearing aids (HAs) or cochlear implants (CIs) can experience broad binaural pitch fusion, such that sounds differing in pitch by as much as 3 to 4 octaves are perceptually integrated across ears. Previously, it was shown in HA users that the fused pitch is a weighted average of the two monaural pitches, ranging from equal weighting to dominance by the lower pitch. The goal of this study was to systematically measure the fused pitches in adult CI users, and determine whether CI users experience similar pitch averaging effects as observed in HA users. Twelve adult CI users (Cochlear Ltd, Sydney, Australia) participated in this study: six bimodal CI users, who wear a CI with a contralateral HA, and six bilateral CI users. Stimuli to HA ears were acoustic pure tones, and stimuli to CI ears were biphasic pulse trains delivered to individual electrodes. Fusion ranges, the ranges of frequencies/electrodes in the comparison ear that were fused with a single electrode (electrode 22, 18, 12, or 6) in the reference ear, were measured using simultaneous, dichotic presentation of reference and comparison stimuli in opposite ears, and varying the comparison stimulus. Once the fusion ranges were measured, the fused binaural pitch of a reference-pair stimulus combination was measured by finding a pitch match to monaural comparison stimuli presented to the paired stimulus ear. Fusion pitch weighting in CI users varied depending on the pitch difference of the reference-pair stimulus combination, with equal pitch averaging occurring for stimuli closer in pitch and lower pitch dominance occurring for stimuli farther apart in pitch. The averaging region was typically 0.5 to 2.3 octaves around the reference for bimodal CI users and 0.4 to 1.5 octaves for bilateral CI users. In some cases, a bias in the averaging region was observed toward the ear with greater stimulus variability. Fusion pitch weighting effects in CI users were similar to those observed previously in HA users. However, CI users showed greater inter-subject variability in both pitch averaging ranges and bias effects. These findings suggest that binaural pitch averaging could be a common underlying mechanism in hearing-impaired listeners.

Spectro-temporal templates unify the pitch of resolved and unresolved harmonics

Pitch is a fundamental attribute in auditory perception that is involved in source identification and segregation, music, and speech understanding. When harmonics are well-resolved, the induced pitch is usually salient and precise; however, when the harmonics are not completely resolved, the pitch percept becomes less salient and poorly discriminated. Previous models relying on harmonic spectral templates have been able to account fully for the pitch of the resolved but not of the unresolved harmonics. I will describe a biologically motivated model of templates that combine both spectral and temporal cues to estimate both pitch percepts. Specifically, the pitch of unresolved harmonics is estimated through bandpass filters implemented by resonances in the dendritic trees of neurons in the early auditory pathway. It is demonstrated that organizing and exploiting such dendritic tuning can arise spontaneously even in response to white noise. We show how these temporal cues become integrated with those of spectrally resolved harmonics, effectively creating spectro-temporal harmonic templates for all pitch percepts. We finally discuss how this approach can account for all major monaural pitch percepts, as well as pitch percepts evoked by dichotic binaural stimuli.

Spectro-temporal templates unify the pitch percepts of resolved and unresolved harmonics.

Pitch is a fundamental attribute in auditory perception involved in source identification and segregation, music, and speech understanding. Pitch percepts are intimately related to harmonic resolvability of sound. When harmonics are well-resolved, the induced pitch is usually salient and precise, and several models relying on autocorrelations or harmonic spectral templates can account for these percepts. However, when harmonics are not completely resolved, the pitch percept becomes less salient, poorly discriminated, with upper range limited to a few hundred hertz, and spectral templates fail to convey percept since only temporal cues are available. Here, a biologically-motivated model is presented that combines spectral and temporal cues to account for both percepts. The model explains how temporal analysis to estimate the pitch of the unresolved harmonics is performed by bandpass filters implemented by resonances in dendritic trees of neurons in the early auditory pathway. It is demonstrated that organizing and exploiting such dendritic tuning can occur spontaneously in response to white noise. This paper then shows how temporal cues of unresolved harmonics may be integrated with spectrally resolved harmonics, creating spectro-temporal harmonic templates for all pitch percepts. Finally, the model extends its account of monaural pitch percepts to pitches evoked by dichotic binaural stimuli.

Effects of broad binaural fusion and hearing loss ondichotic concurrent vowel identification

Many hearing-impaired (HI) individuals have abnormally broad binaural pitch fusion, such that tones differing in pitch by up to 3-4 octaves are fused between ears (Reiss et al., 2017). Broad binaural fusion leads to averaging of the monaural pitches (Oh and Reiss, 2017), and may similarly lead to fusion and averaging of speech streams across ears. In this study, we examined the relationship between binaural fusion range and dichotic vowel identification in normal-hearing (NH) and HI listeners. Synthetic vowels /i/,/u/,/a/, and /ae/ were generated with three fundamental frequencies (F0) of 106.9, 151.2, and 201.8 Hz, and presented dichotically through headphones. For HI listeners, stimuli were shaped according to NAL-NL2 prescriptive targets. Listeners identified 1 vowel or 2 different vowels on each trial. Preliminary results indicate that NH listeners improved their percentage of both vowels identified as the ΔF0 increased, but HI listeners did not. HI listeners were more likely to fuse two vowels together even with large ΔF0. NH listeners with broad fusion also had poorer overall performance than those with sharp fusion. The findings suggest that broad binaural fusion can impede separation of voices and speech streams in both NH and HI listeners. [Work supported by NIH-NIDCD grant R01 DC013307.]

Speech-evoked auditory brainstem response with ipsilateral noise in adults with unilateral hearing loss

Introduction: Subjects with unilateral hearing loss (UHL) report difficulties in speech understanding in noise. Speech-evoked auditory brainstem response (S-ABR) provides cues for temporal and spectral encoding of speech in the brainstem. S-ABR recording in noise increases its sensitivity in evaluating the auditory processing and related disorders.Objectives: Study speech encoding at the level of brainstem when the auditory system relies on one ear and to study the effect of noise on this encoding.Subjects and method: This study included two groups: control group consisted of 15 adults with normal hearing sensitivity and study group consisted of 30 adults with UHL. The study group was further subdivided into two subgroups: study subgroup A (SG A) consisted of 15 adults with right functioning ears and study subgroup B (SG B) consisted of 15 adults with left functioning ears. S-ABR in quiet and with ipsilateral noise was recorded in both the groups using complex ABR advanced auditory research module.Results: In UHL, there was a statistically significant delay in the S-ABR onset and offset in noise compared to quiet. Moreover, quiet–noise (+5 SNR) correlation was significantly low compared to NH. Furthermore, pitch representation (F0 amplitude) was significantly degraded with noise. In addition, there was a statistically significant noise-induced phase shift in the transition region of speech syllable in these subjects.Conclusion: In monaural processing, pitch representation (F0 amplitude) and cross-phaseogram were the main affected domains. Speech phonemes of transient origin can be confused in subjects with UHL.

Abnormal Binaural Spectral Integration in Cochlear Implant Users

Bimodal stimulation, or stimulation of a cochlear implant (CI) together with a contralateral hearing aid (HA), can improve speech perception in noise However, this benefit is variable, and some individuals even experience interference with bimodal stimulation. One contributing factor to this variability may be differences in binaural spectral integration (BSI) due to abnormal auditory experience. CI programming introduces interaural pitch mismatches, in which the frequencies allocated to the electrodes (and contralateral HA) differ from the electrically stimulated cochlear frequencies. Previous studies have shown that some, but not all, CI users adapt pitch perception to reduce this mismatch. The purpose of this study was to determine whether broadened BSI may also reduce the perception of mismatch. Interaural pitch mismatches and dichotic pitch fusion ranges were measured in 21 bimodal CI users. Seventeen subjects with wide fusion ranges also conducted a task to pitch match various fused electrode-tone pairs. All subjects showed abnormally wide dichotic fusion frequency ranges of 1-4 octaves. The fusion range size was weakly correlated with the interaural pitch mismatch, suggesting a link between broad binaural pitch fusion and large interaural pitch mismatch. Dichotic pitch averaging was also observed, in which a new binaural pitch resulted from the fusion of the original monaural pitches, even when the pitches differed by as much as 3-4 octaves. These findings suggest that abnormal BSI, indicated by broadened fusion ranges and spectral averaging between ears, may account for speech perception interference and nonoptimal integration observed with bimodal compared with monaural hearing device use.

Relating binaural pitch perception to the individual listener’s auditory profile

The ability of eight normal-hearing listeners and fourteen listeners with sensorineural hearing loss to detect and identify pitch contours was measured for binaural-pitch stimuli and salience-matched monaurally detectable pitches. In an effort to determine whether impaired binaural pitch perception was linked to a specific deficit, the auditory profiles of the individual listeners were characterized using measures of loudness perception, cognitive ability, binaural processing, temporal fine structure processing, and frequency selectivity, in addition to common audiometric measures. Two of the listeners were found not to perceive binaural pitch at all, despite a clear detection of monaural pitch. While both binaural and monaural pitches were detectable by all other listeners, identification scores were significantly lower for binaural than for monaural pitch. A total absence of binaural pitch sensation coexisted with a loss of a binaural signal-detection advantage in noise, without implying reduced cognitive function. Auditory filter bandwidths did not correlate with the difference in pitch identification scores between binaural and monaural pitches. However, subjects with impaired binaural pitch perception showed deficits in temporal fine structure processing. Whether the observed deficits stemmed from peripheral or central mechanisms could not be resolved here, but the present findings may be useful for hearing loss characterization.

Frequency discrimination duration effects for Huggins pitch and narrowband noise (L)

Frequency difference limens (FDLs) were measured for Huggins pitch (HP) stimuli, consisting of a 30-Hz wide band of interaurally decorrelated noise in a diotic low-pass noise and for 30-Hz wide bands of diotic narrowband noise presented in a diotic low-pass noise background. FDLs at a 400-ms duration for the two stimulus types were equated by adjusting the level of the narrowband noise relative to the background. The effects of duration on the FDLs were then measured for center frequencies of 300, 600, and 900 Hz. Although the results were compromised by floor effects at 900 Hz, at 300 and 600 Hz, the duration effects were very similar for the HP and narrowband noise stimuli, with a large improvement in performance between 100 and 400 ms. In contrast to previous results for pure tones, the effect of duration was independent of frequency. The results suggest that: (1) Binaural and monaural pitches may be processed using a common mechanism; (2) discrimination performance for HP and low-sensation-level narrowband noise stimuli is not determined by the number of waveform periods.

Combination of spectral and binaurally created harmonics in a common central pitch processor.

A fundamental attribute of human hearing is the ability to extract a residue pitch from harmonic complex sounds such as those produced by musical instruments and the human voice. However, the neural mechanisms that underlie this processing are unclear, as are the locations of these mechanisms in the auditory pathway. The ability to extract a residue pitch corresponding to the fundamental frequency from individual harmonics, even when the fundamental component is absent, has been demonstrated separately for conventional pitches and for Huggins pitch (HP), a stimulus without monaural pitch information. HP is created by presenting the same wideband noise to both ears, except for a narrowband frequency region where the noise is decorrelated across the two ears. The present study investigated whether residue pitch can be derived by combining a component derived solely from binaural interaction (HP) with a spectral component for which no binaural processing is required. Fifteen listeners indicated which of two sequentially presented sounds was higher in pitch. Each sound consisted of two “harmonics,” which independently could be either a spectral or a HP component. Component frequencies were chosen such that the relative pitch judgement revealed whether a residue pitch was heard or not. The results showed that listeners were equally likely to perceive a residue pitch when one component was dichotic and the other was spectral as when the components were both spectral or both dichotic. This suggests that there exists a single mechanism for the derivation of residue pitch from binaurally created components and from spectral components, and that this mechanism operates at or after the level of the dorsal nucleus of the lateral lemniscus (brainstem) or the inferior colliculus (midbrain), which receive inputs from the medial superior olive where temporal information from the two ears is first combined.

Long-term measurement of binaural intensity matches and pitch matches. I. Normal hearing

Changes in pitch perception and hearing thresholds over time have been observed in subjects with monaural fluctuating low-frequency hearing loss and Ménière's disease. Long-term suprathreshold audiometry and binaural pitch matches could provide information of these changes. Ten normal subjects were tested for stability of binaural intensity and pitch matches during 9–22 days in their homes with newly developed portable test equipment. Binaural pitch matches were measured using a 0.25- or 1-kHz reference tone presented at 60 dB SPL to one ear, and a loudness-matched test tone of adjustable frequency presented to the other ear. The results showed stable binaural intensity matches (individual inter-quartile ranges, IQRs, 1.2 to 5.7 dB), but binaural pitch matches varied greatly (IQR −0.6 to 5.3% at 0.25 kHz; IQR −1.6 to 7.9% at 1 kHz). Binaural pitch-matching was much better in subjects who could define pitch precisely during monaural pitch matching. It was concluded that in future long-term evaluations of patients with fluctuating inner-ear function, binaural intensity matches could be suitable for all, but binaural pitch matching only for selected patients.

Neural Response Correlates of Detection of Monaurally and Binaurally Created Pitches in Humans

Recent magnetoencephalography (MEG) and functional magnetic resonance imaging studies of human auditory cortex are pointing to brain areas on lateral Heschl's gyrus as the 'pitch-processing center'. Here we describe results of a combined MEG-psychophysical study designed to investigate the timing of the formation of the percept of pitch and the generality of the hypothesized 'pitch-center'. We compared the cortical and behavioral responses to Huggins pitch (HP), a stimulus requiring binaural processing to elicit a pitch percept, with responses to tones embedded in noise (TN)-perceptually similar but physically very different signals. The stimuli were crafted to separate the electrophysiological responses to onset of the pitch percept from the onset of the initial stimulus. Our results demonstrate that responses to monaural pitch stimuli are affected by cross-correlational processes in the binaural pathway. Additionally, we show that MEG illuminates processes not simply observable in behavior. Crucially, the MEG data show that, although physically disparate, both HP and TN are mapped onto similar representations by 150 ms post-onset, and provide critical new evidence that the 'pitch onset response' reflects central pitch mechanisms, in agreement with models postulating a single, central pitch extractor.

Perception of modulations in pitch and lateralization

The ability to perceive low‐frequency sinusoidal modulations of monaurally and dichotically created pitch was compared to the perception of modulations of the subjective lateral position of a binaural image. The stimuli used in the dichotic pitch experiments had low‐pass spectra that were flat between 0 and 2000 Hz, and they were created by modulating the time delay of a multiple‐phase‐shift filter [F. A. Bilsen, J. Acoust. Soc. Am. 59, 467–468 (1976)]. Stimuli with similar spectra and sinusoidally modulated interaural time delays (ITD's) were used for the latralization experiments [D. W. Grantham and F. L. Wightman, J. Acoust. Soc. Am. 63, 511–523 (1978)]. Also examined was the perception of monaural frequency‐modulated pure tones, and monaural low‐pass stimuli with power spectra similar in shape to the “internal spectra” of the dichotic pitch stimuli. Subjects discriminated between sinusoidally modulated and unmodulated stimuli using two‐cue, two‐alternative 4IFC paradigms, and we determined the threshold frequency deviation or ITD as a function of modulation frequency. Results were similar in form for all experiments: threshold frequency deviation or ITD was constant for modulation frequencies up to a particular “corner” frequency, and then increased as a power function of modulation frequency up to at least 32 Hz. This corner frequency was 4 Hz or less for the binaural lateralization and dichotic pitch experiments, and approximately 10 Hz for the two monaural pitch experiments. [Work supported by NIH.]

Some systematic observations on monaural diplacusis.

Anomalies of monaural pitch perception, including pitch changes with level, roughness and beats, were mapped in the intensity-frequency plane by a listener using continuous-tone stimulation between approximately 1 900 and 2 750 Hz. A narrow region characterized by rapid threshold adaptation was also mapped between approximately 2 590 and 2 690 Hz. In the procedure used to localize the internally generated tones, which were interacting with the externally presented single tones to produce beats, the listener adjusted the frequency of a signal presented to this right ear so that the beat rate heard there was the same as a criterion beat rate produced by two external tones in his left ear. A plot in the intensity-frequency plane of adjustments for a constant-beat rate revealed a remarkable correspondence to the region of adaptation (between 2 590 and 2 690 Hz) in that the former curve was simply shifted in frequency away from the latter by an amount equal to the two-tone interval producing the beat rate. Thus, the locations of 'internal tones' correspond predictably to both the lower and upper-frequency boundaries of the region of adaptation. Pitch changes, as a function of signal level, at frequencies below the region of adaptation were also investigated and appear to reflect a change from interaction to cessation of interaction between the signal and the region of adaptation. The locus of these pitch-related abnormalities, over a broad range of frequencies, points to interaction between that range and a smaller-frequency region where abrupt transitions in sensitivity occur.

Acoustic reversals of dichotic pitch patterns by musicians and nonmusicians

Normal subjects acoustically reversed a significantly large proportion of responses to monaural pitch patterns. A dichotic approach to this reversal phenomenon might determine its origin. When 20 musicians and 20 nonmusicians were presented with 450 dichotic pairs of pitch pattern triads, the nonmusicians reversed more patterns than the musicians whether report condition was random or right‐ or left‐directed using manual, verbal, or hummed responses. When right and left ears were compared for both the hummed and verbal responses, there were significantly more left ear reversals in the right‐directed response and significantly more right ear reversals in the left‐directed response. There were no differences between conditions for the manual mode. There were more reversals when the right ear was reported first than when the left ear was reported first and more reversals when the left ear was reported second than when the right ear was reported second. However, there were significantly more reversals for the second reported pattern for all report conditions across response modes. These results indicate that acoustic reversals are probably related to memory decay.

Role of place cue in simple-tone pitch perception assessed with temporary threshold shift

Basilar-membrane nonlinearity observed by Rhode [J. Acoust. Soc. Am. 49, 1218 (1971)] is consistent with basalward shifts of the basilar-membrane vibration envelope with increasing amplitude of a simple-tone stimulus. This nonlinear property, which is indirectly confirmed in this study by measurements of temporary threshold shift (TTS) distributions, is exploited to assess the role of the cochlear “place cue” in simple-tone pitch perception by studying pitch-versus-amplitude behavior. Monaural pitch matchings of 12 subjects show two groups of patterns: For simple tones at frequency f0 = 5 kHz, and at amplitudes varying from 25 to 65 dB sensation level (SL), eight subjects show little pitch shift (less than 2% of f0) for various amplitudes, while the other four subjects show large pitch increase (10%–15% of f0) with increasing amplitude. In contrast, monaural measurements of TTS within 5–20 sec after 30-sec exposures to simple tones of f0 = 5 kHz show similar distributions for all tested subjects (three from each group): the TTS distribution is narrow with a single peak at f0 if Le ⩽ 25 dB SL (where Le is the exposure level), and the TTS distribution spreads mainly to higher frequencies and becomes broader (some with double peaks) with increasing Le above 45 dB SL. It is concluded that for simple-tone pitch matching at 5 kHz the place cue plays no significant role with eight of the subjects, whereas it plays a significant role with only the remaining four.

Pitch Shifts of Periodic Stimuli with Changes in Sound Level

Pitch shifts with changes in sound level were investigated for two types of stimuli, one whose pitch was hypothesized to be analyzed on the basis of “place” and the other whose pitch was presumed to be related to “periodicity.” Eight subjects made alternate monaural pitch matches with four stimuli; pure-tone, dc pulses (both with energy at the fundamental frequency-place pitch), and two varieties of ac pulses (with little energy at the fundamental frequency-periodicity pitch). The fundamental in all cases was approximately 100 cps. Generally, pitch shifts were small, although there were marked differences in the extent and in the variability of the pitch matches as a function of the type of stimulus. Partly because of large differences between subjects, statistically significant shifts were found for only two of the stimuli, one “place” and one “periodicity” stimulus. These shifts were similar in direction, with the pitch shifting downward as level is first increased, then upward with a further increase. Although there appears to be little in the data to support duality of pitch analysis, it is possible that all stimuli were perceived on the basis of periodicity. However, it seems difficult to handle pitch shifts with changes in level within the confines of “periodicity” analysis.