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Congenital amusia is a neurodevelopmental disorder characterized by difficulties in the perception and production of music, including the perception of consonance and dissonance, or the judgment of certain combinations of pitches as more pleasant than others. Two perceptual cues for dissonance are inharmonicity (the lack of a common fundamental frequency between components) and beating (amplitude fluctuations produced by close, interacting frequency components). Amusic individuals have previously been reported to be insensitive to inharmonicity, but to exhibit normal sensitivity to beats. In the present study, we measured adaptive discrimination thresholds in amusic participants and found elevated thresholds for both cues. We recorded EEG and measured the MMN in evoked potentials to consonance and dissonance deviants in an oddball paradigm. The amplitude of the MMN response was similar overall for amusic and control participants; however, in controls, there was a tendency toward larger MMNs for inharmonicity than for beating cues, whereas the opposite tendency was observed for the amusic participants. These findings suggest that initial encoding of consonance cues may be intact in amusia despite impaired behavioral performance, but that the relative weight of nonspectral (beating) cues may be increased for amusic individuals.

Pitch is a fundamental aspect of auditory perception that plays an important role in our ability to understand speech, appreciate music, and attend to one sound while ignoring others. The questions surrounding how pitch is represented in the auditory system, and how our percept relates to the underlying acoustic waveform, have been a topic of inquiry and debate for well over a century. New findings and technological innovations have led to challenges of some long-standing assumptions and have raised new questions. This article reviews some recent developments in the study of pitch coding and perception and focuses on the topic of how pitch information is extracted from peripheral representations based on frequency-to-place mapping (tonotopy), stimulus-driven auditory-nerve spike timing (phase locking), or a combination of both. Although a definitive resolution has proved elusive, the answers to these questions have potentially important implications for mitigating the effects of hearing loss via devices such as cochlear implants.

Adult listeners perceive pitch with fine precision, with many adults capable of discriminating less than a 1 % change in fundamental frequency (F0). Although there is variability across individuals, this precise pitch perception is an ability ascribed to cortical functions that are also important for speech and music perception. Infants display neural immaturity in the auditory cortex, suggesting that pitch discrimination may improve throughout infancy. In two experiments, we tested the limits of F0 (pitch) and spectral centroid (timbre) perception in 66 infants and 31 adults. Contrary to expectations, we found that infants at both 3 and 7 months were able to reliably detect small changes in F0 in the presence of random variations in spectral content, and vice versa, to the extent that their performance matched that of adults with musical training and exceeded that of adults without musical training. The results indicate high fidelity of F0 and spectral-envelope coding in infants, implying that fully mature cortical processing is not necessary for accurate discrimination of these features. The surprising difference in performance between infants and musically untrained adults may reflect a developmental trajectory for learning natural statistical covariations between pitch and timbre that improves coding efficiency but results in degraded performance in adults without musical training when expectations for such covariations are violated.

Modulations in both amplitude and frequency are prevalent in natural sounds and are critical in defining their properties. Humans are exquisitely sensitive to frequency modulation (FM) at the slow modulation rates and low carrier frequencies that are common in speech and music. This enhanced sensitivity to slow-rate and low-frequency FM has been widely believed to reflect precise, stimulus-driven phase locking to temporal fine structure in the auditory nerve. At faster modulation rates and/or higher carrier frequencies, FM is instead thought to be coded by coarser frequency-to-place mapping, where FM is converted to amplitude modulation (AM) via cochlear filtering. Here we show that patterns of human FM perception that have classically been explained by limits in peripheral temporal coding are instead better accounted for by constraints in the central processing of fundamental frequency (F0) or pitch. We measured FM detection in male and female humans using harmonic complex tones with an F0 within the range of musical pitch, but with resolved harmonic components that were all above the putative limits of temporal phase locking (> 8 kHz). Listeners were more sensitive to slow than fast FM rates, even though all components were beyond the limits of phase locking. In contrast, AM sensitivity remained better at faster than slower rates, regardless of carrier frequency. These findings demonstrate that classic trends in human FM sensitivity, previously attributed to auditory-nerve phase locking, may instead reflect the constraints of a unitary code that operates at a more central level of processing.SIGNIFICANCE STATEMENT:Natural sounds involve dynamic frequency and amplitude fluctuations. Humans are particularly sensitive to frequency modulation (FM) at slow rates and low carrier frequencies, which are prevalent in speech and music. This sensitivity has been ascribed to encoding of stimulus temporal fine structure (TFS) via phase-locked auditory-nerve activity. To test this long-standing theory, we measured FM sensitivity using complex tones with a low fundamental frequency (F0) but only high-frequency harmonics, beyond the limits of phase locking. Dissociating the F0 from high-frequency TFS showed that FM sensitivity is limited not by peripheral encoding of TFS, but rather by central processing of F0, or pitch. The results suggest a unitary code for FM detection limited by more central constraints.

Humans and many other animals can hear a wide range of sounds. We can hear low and high notes and both quiet and loud sounds. We are also very good at telling the difference between sounds that are similar, like the speech sounds “argh” and “ah,” and picking apart sounds that are mixed together, like when an orchestra is playing. But how do human hearing abilities compare to those of other animals? In this article, we discover how the inner ear determines hearing abilities. Many other mammals can hear very high notes that we cannot, and some can hear quiet sounds that we cannot. However, humans may be better than any other species at distinguishing similar sounds. We know this because, milliseconds after the sounds around us go into our ears, other sounds come out: sounds that are actually produced by those same ears!

Cochlear implant (CI) listeners typically perform poorly on tasks involving the pitch of complex tones. This limitation in performance is thought to be mainly due to the restricted number of active channels and the broad current spread that leads to channel interactions and subsequent loss of precise spectral information, with temporal information limited primarily to temporal-envelope cues. Little is known about the degree of spectral resolution required to perceive combinations of multiple pitches, or a single pitch in the presence of other interfering tones in the same spectral region. This study used noise-excited envelope vocoders that simulate the limited resolution of CIs to explore the perception of multiple pitches presented simultaneously. The results show that the resolution required for perceiving multiple complex pitches is comparable to that found in a previous study using single complex tones. Although relatively high performance can be achieved with 48 channels, performance remained near chance when even limited spectral spread (with filter slopes as steep as 144 dB/octave) was introduced to the simulations. Overall, these tight constraints suggest that current CI technology will not be able to convey the pitches of combinations of spectrally overlapping complex tones.

Human sensitivity to frequency modulation (FM) is best for low carrier frequencies (

Magneto- and electroencephalographic (M/EEG) measures of neural responses to speech and other natural sounds provide a noninvasive window into the neural tracking of temporal dynamics of natural sounds. However, the interpretation of these measures and their relation to perception remain unclear. In this study, amplitude modulation (AM) of a low-pass noise carrier (cutoff 4 kHz) was used to measure EEG envelope following responses (EFRs) for two AM rates presented simultaneously or in isolation. The spectral separations between the two AM rates were selected to produce varying degrees of perceptual modulation masking. The AM rates used spanned the range from 8 to 203 Hz, reflecting cortical and subcortical EFR generators. For double-rate AM, the EFRs had two distinct spectral peaks, corresponding to the component AM rates. In all conditions, the peak EFR amplitudes for two simultaneous AM rates did not differ significantly from those presented singly, even when the two rates produced significant perceptual masking. The results show that EEG measures of neural responses synchronized to temporal envelope fluctuations fail to reflect the important perceptual phenomenon of modulation masking. [Work supported by NIH R01 DC012262 (Oxenham) and R01 DC015987 (Wojtczak).]

Congenital amusia is a neurodevelopmental disorder characterized by difficulties in the perception and production of music, including the perception of consonance and dissonance, or the judgment of certain combinations of pitches as more pleasant than others. Two perceptual cues for dissonance are inharmonicity (the lack of a common fundamental frequency between components) and beating (amplitude fluctuations produced by close, interacting frequency components). In the presence of inharmonicities or beats, amusics have previously been reported to be insensitive to inharmonicity, but to exhibit normal sensitivity to beats. In the present study, we measured adaptive discrimination thresholds in amusic participants and found elevated thresholds for both cues. We recorded EEG and measured the mismatch negativity (MMN) in evoked potentials to consonance and dissonance deviants in an oddball paradigm. The amplitude of the MMN response was similar overall for amusics and controls, but while control participants showed a stronger MMN to harmonicity cues than to beating cues, amusic participants showed a stronger MMN to beating cues than to harmonicity cues. These findings suggest that initial encoding of consonance cues may be intact in amusia despite impaired behavioral performance, but that the relative weight of non-spectral cues may be increased for amusic individuals.

The University of Minnesota (UMN) has graduate programs that span the areas of Animal Bioacoustics, Psychological and Physiological Acoustics, and Speech Communication. Degrees are offered in Psychology (PhD), Speech-Language-Hearing Sciences (MA in speech-language pathology, AuD, and PhD in speech-language-hearing sciences), Biomedical Engineering (MS and PhD), Ecology, Evolution, and Behavior (PhD), and Neuroscience (PhD). Faculty across departments have a shared interest in understanding how the ear and brain work together to process sound and in developing new technologies and approaches for improving hearing disorders. Located on campus is the Center for Applied and Translational Sensory Science (CATSS), which provides opportunities for interdisciplinary collaborations across departments and industry to understand how sensory impairments work. Within CATSS is the Multi-Sensory Perception Lab, which houses shared equipment, including eye trackers and electroencephalography. The Center for Magnetic Resonance Research houses several ultrahigh field magnets, while the Center for Neural Engineering and affiliated faculty labs also house multiple neuromodulation and neurorecording devices to interact with and monitor neural activity in humans and animals.

The perception of sensory events can be suppressed or enhanced by the surrounding spatial and temporal context in ways that help in detecting novel objects and establishing perceptual constancy. In the auditory system, the phenomenon known as auditory enhancement reflects a general principle of contrast enhancement, where a target sound embedded within a background sound becomes perceptually more salient if the background is presented first by itself. This effect is highly robust, producing an effective enhancement of the target of between 5 and 25 dB (more than two orders of magnitude in intensity), depending on the task. Despite their ubiquity in vision, neural correlates of auditory contrast enhancement have yet to be identified in humans. Here we used the auditory steady-state response to probe the neural response to a target sound under conditions of enhancement. The probe was simultaneously modulated in amplitude with two modulation frequencies, to distinguish cortical from subcortical contributions to this phenomenon. We found robust auditory cortical, but not subcortical, enhancement that correlates with behavior and is consistent with an early theoretical model that postulates neural adaptation of inhibition. Our findings provide empirical support for a previously unverified theory of auditory enhancement and point to new approaches for improving sensory prostheses for hearing loss, such as hearing aids and cochlear implants.Significance StatementA target sound embedded within a background sound becomes perceptually more salient if the background is presented first by itself. This phenomenon, where the target “pops out”, is known as auditory enhancement. It reflects a general principle of contrast enhancement, and helps in the detection of new acoustic events in the environment and in establishing the perceptual constancy of speech and other biologically relevant sounds under varying acoustic conditions. We use EEG in humans to reveal a cortical correlate of this perceptual phenomenon that provides empirical support for a longstanding but previously unverified theoretical account.

Fundamental frequency differences (ΔF0) between competing talkers aid in the perceptual segregation of the talkers (ΔF0 benefit), but the underlying mechanisms remain incompletely understood. A model of ΔF0 benefit based on harmonic cancellation proposes that a masker's periodicity can be used to cancel (i.e., filter out) its neural representation. Earlier work suggested that an octave ΔF0 provided little benefit, an effect predicted by harmonic cancellation due to the shared periodicity of masker and target. Alternatively, this effect can be explained by spectral overlap between the harmonic components of the target and masker. To assess these competing explanations, speech intelligibility of a monotonized target talker, masked by a speech-shaped harmonic complex tone, was measured as a function of ΔF0, masker spectrum (all harmonics or odd harmonics only), and masker temporal envelope (amplitude modulated or unmodulated). Removal of the masker's even harmonics when the target was one octave above the masker improved speech reception thresholds by about 5 dB. Because this manipulation eliminated spectral overlap between target and masker components but preserved shared periodicity, the finding is consistent with the explanation for the lack of ΔF0 benefit at the octave based on spectral overlap, but not with the explanation based on harmonic cancellation.

In natural listening contexts, especially in music, it is common to hear three or more simultaneous pitches, but few empirical or theoretical studies have addressed how this is achieved. Place and pattern-recognition theories of pitch require at least some harmonics to be spectrally resolved for pitch to be extracted, but it is unclear how often such conditions exist when multiple complex tones are presented together. In three behavioral experiments, mixtures of three concurrent complexes were filtered into a single bandpass spectral region, and the relationship between the fundamental frequencies and spectral region was varied in order to manipulate the extent to which harmonics were resolved either before or after mixing. In experiment 1, listeners discriminated major from minor triads (a difference of 1 semitone in one note of the triad). In experiments 2 and 3, listeners compared the pitch of a probe tone with that of a subsequent target, embedded within two other tones. All three experiments demonstrated above-chance performance, even in conditions where the combinations of harmonic components were unlikely to be resolved after mixing, suggesting that fully resolved harmonics may not be necessary to extract the pitch from multiple simultaneous complexes.

Objectives This study tested listeners with a cochlear implant (CI) in one ear and acoustic hearing in the other ear, to assess their ability to localize sound and to understand speech in collocated or spatially separated noise or speech maskers. Design Eight CI listeners with contralateral acoustic hearing ranging from normal hearing to moderate sensorineural hearing loss were tested. Localization accuracy was measured in five of the listeners using stimuli that emphasized the separate contributions of interaural level differences (ILDs) and interaural time differences (ITD) in the temporal envelope and/or fine structure. Sentence recognition was tested in all eight CI listeners, using collocated and spatially separated speech-shaped Gaussian noise and two-talker babble. Performance was compared with that of age-matched normal-hearing listeners via loudspeakers or via headphones with vocoder simulations of CI processing. Results Localization improved with the CI but only when high-frequency ILDs were available. Listeners experienced no additional benefit via ITDs in the stimulus envelope or fine structure using real or vocoder-simulated CIs. Speech recognition in two-talker babble improved with a CI in seven of the eight listeners when the target was located at the front and the babble was presented on the side of the acoustic-hearing ear, but otherwise showed little or no benefit of a CI. Conclusion Sound localization can be improved with a CI in cases of significant residual hearing in the contralateral ear, but only for sounds with high-frequency content, and only based on ILDs. In speech understanding, the CI contributed most when it was in the ear with the better signal to noise ratio with a speech masker.

Pitch and timbre are two primary features of auditory perception that are generally considered independent. However, an increase in pitch (produced by a change in fundamental frequency) can be confused with an increase in brightness (an attribute of timbre related to spectral centroid) and vice versa. Previous work indicates that pitch and timbre are processed in overlapping regions of the auditory cortex, but are separable to some extent via multivoxel pattern analysis. Here, we tested whether attention to one or other feature increases the spatial separation of their cortical representations and if attention can enhance the cortical representation of these features in the absence of any physical change in the stimulus. Ten human subjects (four female, six male) listened to pairs of tone triplets varying in pitch, timbre, or both and judged which tone triplet had the higher pitch or brighter timbre. Variations in each feature engaged common auditory regions with no clear distinctions at a univariate level. Attending to one did not improve the separability of the neural representations of pitch and timbre at the univariate level. At the multivariate level, the classifier performed above chance in distinguishing between conditions in which pitch or timbre was discriminated. The results confirm that the computations underlying pitch and timbre perception are subserved by strongly overlapping cortical regions, but reveal that attention to one or other feature leads to distinguishable activation patterns even in the absence of physical differences in the stimuli.SIGNIFICANCE STATEMENTAlthough pitch and timbre are generally thought of as independent auditory features of a sound, pitch height and timbral brightness can be confused for one another. This study shows that pitch and timbre variations are represented in overlapping regions of auditory cortex, but that they produce distinguishable patterns of activation. Most importantly, the patterns of activation can be distinguished based on whether subjects attended to pitch or timbre even when the stimuli remained physically identical. The results therefore show that variations in pitch and timbre are represented by overlapping neural networks, but that attention to different features of the same sound can lead to distinguishable patterns of activation.

At very high frequencies, fundamental-frequency difference limens (F0DLs) for five-component harmonic complex tones can be better than predicted by optimal integration of information, assuming performance is limited by noise at the peripheral level, but are in line with predictions based on more central sources of noise. This study investigates whether there is a minimum number of harmonic components needed for such super-optimal integration effects and if harmonic range or inharmonicity affects this super-optimal integration. Results show super-optimal integration, even with two harmonic components and for most combinations of consecutive harmonic, but not inharmonic, components.

Behavioral forward-masking thresholds with a spectrally notched noise masker and a fixed low-level probe tone have been shown to provide accurate estimates of cochlear tuning. Estimates using simultaneous masking are similar but generally broader, presumably due to nonlinear cochlear suppression effects. So far, estimates with forward masking have been limited to frequencies of 1 kHz and above. This study used spectrally notched noise under forward and simultaneous masking to estimate frequency selectivity between 200 and 1000 Hz for young adult listeners with normal hearing. Estimates of filter tuning at 1000 Hz were in agreement with previous studies. Estimated tuning broadened below 1000 Hz, with the filter quality factor based on the equivalent rectangular bandwidth (Q(ERB)) decreasing more rapidly with decreasing frequency than predicted by previous equations, in line with earlier predictions based on otoacoustic-emission latencies. Estimates from simultaneous masking remained broader than those from forward masking by approximately the same ratio. The new data provide a way to compare human cochlear tuning estimates with auditory-nerve tuning curves from other species across most of the auditory frequency range.

Frequency-to-place mapping, or tonotopy, is a fundamental organizing principle throughout the auditory system, from the earliest stages of auditory processing in the cochlea to subcortical and cortical regions. Although cortical maps are referred to as tonotopic, it is unclear whether they simply reflect a mapping of physical frequency inherited from the cochlea, a computation of pitch based on the fundamental frequency, or a mixture of these two features. We used high-resolution functional magnetic resonance imaging (fMRI) to measure BOLD responses as male and female human participants listened to pure tones that varied in frequency or complex tones that varied in either spectral content (brightness) or fundamental frequency (pitch). Our results reveal evidence for pitch tuning in bilateral regions that partially overlap with the traditional tonotopic maps of spectral content. In general, primary regions within Heschl's gyri (HGs) exhibited more tuning to spectral content, whereas areas surrounding HGs exhibited more tuning to pitch.SIGNIFICANCE STATEMENTTonotopy, an orderly mapping of frequency, is observed throughout the auditory system. However, it is not known whether the tonotopy observed in the cortex simply reflects the frequency spectrum (as in the ear) or instead represents the higher-level feature of fundamental frequency, or pitch. Using carefully controlled stimuli and high-resolution functional magnetic resonance imaging (fMRI), we separated these features to study their cortical representations. Our results suggest that tonotopy in primary cortical regions is driven predominantly by frequency, but also reveal evidence for tuning to pitch in regions that partially overlap with the tonotopic gradients but extend into nonprimary cortical areas. In addition to resolving ambiguities surrounding cortical tonotopy, our findings provide evidence that selectivity for pitch is distributed bilaterally throughout auditory cortex.

Although beamforming algorithms for hearing aids can enhance performance, the wearer's head may not always face the target talker, potentially limiting real-world benefits. This study aimed to determine the extent to which eye tracking improves the accuracy of locating the current talker in three-way conversations and to test the hypothesis that eye movements become more likely to track the target talker with increasing background noise levels, particularly in older and/or hearing-impaired listeners. Conversations between a participant and two confederates were held around a small table in quiet and with background noise levels of 50, 60, and 70 dB sound pressure level, while the participant's eye and head movements were recorded. Ten young normal-hearing listeners were tested, along with ten older normal-hearing listeners and eight hearing-impaired listeners. Head movements generally undershot the talker's position by 10°–15°, but head and eye movements together predicted the talker's position well. Contrary to our original hypothesis, no major differences in listening behavior were observed between the groups or between noise levels, although the hearing-impaired listeners tended to spend less time looking at the current talker than the other groups, especially at the highest noise level.

Profile analysis and spectrotemporal ripple discrimination are psychoacoustic tasks used to probe the auditory system’s spectral and intensity resolution. In the present experiment, we compared performance at low- and high-frequencies in four related psychoacoustic tasks: level discrimination, profile analysis, spectrotemporal ripple detection, and spectrotemporal ripple direction discrimination. The level discrimination and ripple detection tasks were designed so that cues from single auditory filters were sufficient for performing the tasks. The profile analysis and ripple direction discrimination tasks were designed to render cues from single auditory filters insufficient to perform the tasks. Based on data from a group of ∼20 young normal-hearing, listeners, we found that profile analysis was markedly worse at high-frequencies than low-frequencies, even when accounting for differences in level discrimination at low- and high-frequencies. In contrast, no significant differences were observed between low- and high-frequencies for either the ripple detection or ripple direction discrimination tasks. We further analyzed our behavioral data using computational simulations of auditory-nerve and midbrain responses. This analysis suggested that differences in performance at low- and high-frequencies cannot be explained at the level of the auditory periphery, but instead emerge at more central loci. [Work supported by NIH grants F31 DC019247 and R01 DC005216.]

Prior work has demonstrated that harmonic tones are easier to detect in noise and yield better F0 discrimination in noise than inharmonic tones. These effects, referred to as harmonic benefit, appear to be approximately the same size in musicians and non-musicians, despite musicians’ overall better pitch discrimination. The present study aimed to replicate these findings and extend them to include measurements of harmonic benefit in other tasks. Non-musicians and musicians were compared in four tasks: detection in noise, F0 discrimination, FM detection, and AM detection. The stimuli in each task were either harmonic or inharmonic complex tones and were presented in threshold-equalizing noise at a range of signal-to-noise ratios. We found that harmonic benefit for F0 discrimination was large and remained large even after accounting for differences in the detectability of harmonic and inahrmonic tones. In contrast, harmonic benefit was small for FM and AM detection and could mostly be accounted for by differences in detectability. In contrast to prior studies, we found that musicians showed a larger harmonic benefit than non-musicians. These results provide insight into how musical training may specialize the auditory system for processing of harmonicity and pitch. [Work supported by NIH grants F31 DC019247 and R01 DC005216.]

Adaptation, the selective decrease in neural responses following repeated stimulation, is likely important for perception in the face of variable sensory input. Previous researchers have observed contrastive adaptation effects involving speaker identity, gender, and vowels. The present study investigated whether such contrast effects can occur between voice and non-voice stimuli. A 10-step continuum between “voice” (/a/, /o/, or /u/ vowels) and “instrument” (bassoon, horn, or viola) was generated for each possible pair. In each trial, an adaptor, either voice or instrument, was played four times, followed by a test stimulus from along the appropriate continuum. When trials with voice and instrumental adaptors were grouped into separate blocks, strong contrastive adaptation effects were observed, with the test stimuli more likely to be identified as voice following instrumental adaptors and vice versa. Preliminary results comparing interleaved with blocked conditions and same-ear with different-ear conditions suggest longer-term build-up and persistence effects that may extend across both ears. [Work supported by NIH grant R01 DC012262.]

Adults perceive pitch with fine precision, an ability ascribed to cortical functions that are also important for speech and music perception. Infants display neural immaturity in the auditory cortex, suggesting that pitch discrimination may improve throughout infancy. In three experiments, we tested the limits of pitch and timbre perception in 66 infants and 44 adults. Contrary to expectations, we found that infants surpassed adults in detecting subtle changes in pitch in the presence of random variations in timbre, and vice versa. The results indicate high fidelity of pitch and timbre coding in infants, implying that fully mature cortical processing is not necessary for accurate discrimination of these features. The surprising superiority of infants over adults may reflect a developmental trajectory for learning natural statistical covariations between pitch and timbre that improves coding efficiency in adults, but results in degraded perceptual acuity when expectations for such covariations are violated.

Purpose The goal of this study was to develop and validate a new corpus of sentences without semantic context to facilitate research aimed at isolating the effects of semantic context in speech perception. Method The newly developed corpus contains nonsensical sentences but is matched in vocabulary and syntactic structure to the existing Basic English Lexicon (BEL) corpus. It consists of 20 lists, with each list containing 25 sentences and each sentence having four keywords. Each new list contains the same keywords as the respective list in the original BEL corpus, but the keywords within each list are scrambled across sentences to eliminate semantic context within each sentence, while maintaining the original syntactic structure. All sentences in the original and nonsense BEL corpora were recorded by the same two male and two female talkers. Results Mean intelligibility scores for each list were estimated by calculating the mean proportion of correct keywords achieved by 40 normal-hearing listeners for one male and one female talker. Although small but significant differences were found between some pairs of lists, mean performance for all 20 lists fell within the 95% confidence intervals of the mean. Conclusions Lists in the newly developed nonsense corpus are reasonably well equated for difficulty and can be used interchangeably in a randomized experimental design. Both the original and nonsense BEL sentences, all recorded by the same four talkers, are publicly available. Supplemental Material https://doi.org/10.23641/asha.13022900

Differences in fundamental frequency (F0) or pitch between competing voices facilitate our ability to segregate a target voice from interferers, thereby enhancing speech intelligibility. Although lower-numbered harmonics elicit a stronger and more accurate pitch sensation than higher-numbered harmonics, it is unclear whether the stronger pitch leads to an increased benefit of pitch differences when segregating competing talkers. To answer this question, sentence recognition was tested in young normal-hearing listeners in the presence of a single competing talker. The stimuli were presented in a broadband condition or were highpass or lowpass filtered to manipulate the pitch accuracy of the voicing, while maintaining roughly equal speech intelligibility in the highpass and lowpass regions. Performance was measured with average F0 differences (ΔF0) between the target and single-talker masker of 0, 2, and 4 semitones. Pitch discrimination abilities were also measured to confirm that the lowpass-filtered stimuli elicited greater pitch accuracy than the highpass-filtered stimuli. No interaction was found between filter type and ΔF0 in the sentence recognition task, suggesting little or no effect of harmonic rank or pitch accuracy on the ability to use F0 to segregate natural voices, even when the average ΔF0 is relatively small. The results suggest that listeners are able to obtain some benefit of pitch differences between competing voices, even when pitch salience and accuracy is low. The accuracy with which we are able to discriminate the pitch of a harmonic complex tone depends on the F0 and the harmonic numbers present. For F0s in the average range of speech (100–200 Hz), pitch discrimination is best (implying accurate F0 coding) when harmonics below about the 10th are present [6–10]. When these lower-numbered harmonics are present, pitch discrimination is also independent of the phase relationships between the harmonics, suggesting that these harmonics are spectrally resolved to some extent. In contrast, when only harmonics above the 10th are present in this range of F0s, pitch discrimination is poorer and is affected by the phase relationships between harmonics, suggesting that interactions occur between these spectrally unresolved harmonics [6–10]. Psychoacoustic studies of sound segregation have often been carried out with interleaved sequences of tones. Some of these studies have investigated segregation based on differences in pitch accuracy and have varied the accuracy by systematically varying whether resolved or only unresolved harmonics are present. Previous studies have found that stream segregation can occur with alternating sequences of tones, even if the tones consist only of unresolved harmonics [11–14]. However, the question of whether streaming is greater with resolved than unresolved harmonics has received mixed answers. In cases where the listeners’ task was to segregate the streams, some studies have shown little difference in streaming between conditions containing resolved or only unresolved harmonics [11, 15], whereas another study using a similar approach found significantly greater stream segregation when resolved harmonics were present than when only unresolved harmonics were present [12]. However, in situations where the task was either neutral or encouraged listeners to integrate the sequences into a single stream, the results have been consistent across studies in showing greater segregation for complex tones containing resolved harmonics than for tones containing only unresolved harmonics [13, 14]. These findings support the idea that pitch accuracy can affect our ability to segregate sounds. Less is known about the role of low-numbered harmonics in the context of segregating competing speech. Bird and Darwin [2] showed that lower harmonics dominate performance in a speech-segregation task based on F0 differences, but they did not test any conditions containing only high-numbered harmonics. Oxenham and Simonson [16] explored the effect of harmonic rank on speech intelligibility by comparing conditions where the target and single-talker masker had been lowpass (LP) or highpass (HP) filtered to either retain (LP-filtered) or remove (HP-filtered) the spectrally resolved components from the target and masker [16]. The LP and HP cutoff frequencies were selected to produce roughly equal performance in noise for both conditions. Surprisingly, performance in the LP and HP conditions improved by similar amounts when the noise masker was replaced by a single-talker masker with a different average F0, suggesting no clear benefit of having resolved harmonic components in the speech. However, that study only used relatively large values of average ΔF0 that according to recent F0 estimates were approximately 4 and 8 semitones (ST). Moreover, this study did not parametrically vary the ΔF0 between the target and masker. It may be that pitch accuracy is only relevant for more challenging conditions, i.e. for conditions with smaller average values of ΔF0. Thus, it remains unclear whether the effect of ΔF0 on performance is affected by the presence or absence of low-numbered, spectrally resolved harmonics. The aim of the present study was to determine whether there is an effect of spectral region, and hence pitch coding accuracy, on the ability of listeners to use average F0 differences between a target and an interfering talker to understand natural speech.

SUMMARYFrequency-to-place mapping, or tonotopy, is a fundamental organizing principle from the earliest stages of auditory processing in the cochlea to subcortical and cortical regions. Although cortical maps are referred to as tonotopic, previous studies employed sounds that covary in spectral content and higher-level perceptual features such as pitch, making it unclear whether these maps are inherited from cochlear organization and are indeed tonotopic, or instead reflect transformations based on higher-level features. We used high-resolution fMRI to measure BOLD responses in 10 participants as they listened to pure tones that varied in frequency or complex tones that independently varied in either spectral content or fundamental frequency (pitch). We show that auditory cortical gradients are in fact a mixture of maps organized both by spectral content and pitch. Consistent with hierarchical organization, primary regions were tuned predominantly to spectral content, whereas higher-level pitch tuning was observed bilaterally in surrounding non-primary regions.

For cochlear-implant users with near-normal contralateral hearing, a mismatch between the frequency-to-place mapping in the two ears could produce a suboptimal performance. This study assesses tonotopic matches via binaural interactions. Dynamic interaural time-difference sensitivity was measured using bandpass-filtered pulse trains at different rates in the acoustic and implanted ear, creating binaural envelope beats. Sensitivity to beats should peak when the same tonotopic region is stimulated in both ears. All nine participants detected dynamic interaural timing differences and demonstrated some frequency selectivity. This method provides a guide to frequency-to-place mapping without compensation for inherent latency differences between the acoustic and implanted ears.

We are generally able to identify sounds and understand speech with ease, despite the large variations in the acoustics of each sound, which occur due to factors such as different talkers, background noise, and room acoustics. This form of perceptual constancy is likely to be mediated in part by the auditory system's ability to adapt to the ongoing environment or context in which sounds are presented. Auditory context effects have been studied under different names, such as spectral contrast effects in speech and auditory enhancement effects in psychoacoustics, but they share some important properties and may be mediated by similar underlying neural mechanisms. This review provides a survey of recent studies from our laboratory that investigate the mechanisms of speech spectral contrast effects and auditory enhancement in people with normal hearing, hearing loss, and cochlear implants. We argue that a better understanding of such context effects in people with normal hearing may allow us to restore some of these important effects for people with hearing loss via signal processing in hearing aids and cochlear implants, thereby potentially improving auditory and speech perception in the complex and variable everyday acoustic backgrounds that surround us.

This study investigated the relationship between fundamental frequency difference limens (F0DLs) and the lowest harmonic number present over a wide range of F0s (30–2000 Hz) for 12-component harmonic complex tones that were presented in either sine or random phase. For fundamental frequencies (F0s) between 100 and 400 Hz, a transition from low (∼1%) to high (∼5%) F0DLs occurred as the lowest harmonic number increased from about seven to ten, in line with earlier studies. At lower and higher F0s, the transition between low and high F0DLs occurred at lower harmonic numbers. The worsening performance at low F0s was reasonably well predicted by the expected decrease in spectral resolution below about 500 Hz. At higher F0s, the degradation in performance at lower harmonic numbers could not be predicted by changes in spectral resolution but remained relatively good (

Natural sounds convey information via frequency and amplitude modulations (FM and AM). Humans are acutely sensitive to the slow rates of FM that are crucial for speech and music. This sensitivity has long been thought to rely on precise stimulus-driven auditory-nerve spike timing (time code), whereas a coarser code, based on variations in the cochlear place of stimulation (place code), represents faster FM rates. We tested this theory in listeners with normal and impaired hearing, spanning a wide range of place-coding fidelity. Contrary to predictions, sensitivity to both slow and fast FM correlated with place-coding fidelity. We also used incoherent AM on two carriers to simulate place coding of FM and observed poorer sensitivity at high carrier frequencies and fast rates, two properties of FM detection previously ascribed to the limits of time coding. The results suggest a unitary place-based neural code for FM across all rates and carrier frequencies.

The auditory steady-state response (ASSR) has been traditionally recorded with few electrodes and is often measured as the voltage difference between mastoid and vertex electrodes (vertical montage). As high-density EEG recording systems have gained popularity, multi-channel analysis methods have been developed to integrate the ASSR signal across channels. The phases of ASSR across electrodes can be affected by factors including the stimulus modulation rate and re-referencing strategy, which will in turn affect the estimated ASSR strength. To explore the relationship between the classical vertical-montage ASSR and whole-scalp ASSR, we applied these two techniques to the same data to estimate the strength of ASSRs evoked by tones with sinusoidal amplitude modulation rates of around 40, 100, and 200 Hz. The whole-scalp methods evaluated in our study, with either linked-mastoid or common-average reference, included ones that assume equal phase across all channels, as well as ones that allow for different phase relationships. The performance of simple averaging was compared to that of more complex methods involving principal component analysis. Overall, the root-mean-square of the phase locking values (PLVs) across all channels provided the most efficient method to detect ASSR across the range of modulation rates tested here.

Absolute pitch (AP)—an ability to identify an isolated pitch without musical context—is commonly believed to be a valuable ability for musicians. However, relative pitch (RP)—an ability to perceive pitch relations—is more important in most musical contexts. In this study, music students in East Asian and Western countries (Japan, China, Poland, Germany, and USA) were tested on AP and RP abilities. In the AP test, 60 single tones were presented in a quasirandom order over a five-octave range. In the RP test, ascending musical intervals from 1 to 11 semitones were presented in four different keys. Participants wrote down note names in the AP test and scale-degree names or musical interval names in the RP test. The conservatory-level Japanese students showed the highest AP performance and more than half of them were classified as accurate AP possessors, but only 10% were classified as accurate RP possessors. In contrast, only a small percentage of participants from Poland, Germany, and the USA were identified as accurate AP possessors, whereas many more were accurate RP possessors. Participants from China were typically intermediate on both measures. These noticeable contrasts between AP and RP performance in different countries suggest influences of the underlying socio-cultural conditions, presumably relating to music education. Given the importance of RP in music, the results suggest that more emphasis should be place on RP training, particularly in East Asian countries.

Poor spectral resolution contributes to the difficulties experienced by cochlear implant (CI) users when listening to speech in noise. However, correlations between measures of spectral resolution and speech perception in noise have not always been found to be robust. It may be that the relationship between spectral resolution and speech perception in noise becomes clearer in conditions where the speech and noise are not spectrally matched, so that improved spectral resolution can assist in separating the speech from the masker. To test this prediction, speech intelligibility was measured with noise or tone maskers that were presented either in the same spectral channels as the speech or in interleaved spectral channels. Spectral resolution was estimated via a spectral ripple discrimination task. Results from vocoder simulations in normal-hearing listeners showed increasing differences in speech intelligibility between spectrally overlapped and interleaved maskers as well as improved spectral ripple discrimination with increasing spectral resolution. However, no clear differences were observed in CI users between performance with spectrally interleaved and overlapped maskers, or between tone and noise maskers. The results suggest that spectral resolution in current CIs is too poor to take advantage of the spectral separation produced by spectrally interleaved speech and maskers. Overall, the spectrally interleaved and tonal maskers produce a much larger difference in performance between normal-hearing listeners and CI users than do traditional speech-in-noise measures, and thus provide a more sensitive test of speech perception abilities for current and future implantable devices.

Both music and speech perception rely on hearing out one pitch in the presence of others. Pitch discrimination of narrowband sounds based only on temporal-envelope cues is rendered nearly impossible by introducing interferers in both normal-hearing listeners and cochlear-implant (CI) users. This study tested whether performance improves in normal-hearing listeners if the target is presented over a broad spectral region. The results indicate that performance is still strongly affected by spectrally remote interferers, despite increases in bandwidth, suggesting that envelope-based pitch is unlikely to allow CI users to perceive pitch when multiple harmonic sounds are presented at once.

Attention to a target stimulus within a complex scene often results in enhanced cortical representations of the target relative to the background. It remains unclear where along the auditory pathways attentional effects can first be measured. Anatomy suggests that attentional modulation could occur through corticofugal connections extending as far as the cochlea itself. Earlier attempts to investigate the effects of attention on human cochlear processing have revealed small and inconsistent effects. In this study, stimulus-frequency otoacoustic emissions were recorded from a total of 30 human participants as they performed tasks that required sustained selective attention to auditory or visual stimuli. In the first sample of 15 participants, emission magnitudes were significantly weaker when participants attended to the visual stimuli than when they attended to the auditory stimuli, by an average of 5.4 dB. However, no such effect was found in the second sample of 15 participants. When the data were pooled across samples, the average attentional effect was significant, but small (2.48 dB), with 12 of 30 listeners showing a significant effect, based on bootstrap analysis of the individual data. The results highlight the need for considering sources of individual differences and using large sample sizes in future investigations.Attention to a target stimulus within a complex scene often results in enhanced cortical representations of the target relative to the background. It remains unclear where along the auditory pathways attentional effects can first be measured. Anatomy suggests that attentional modulation could occur through corticofugal connections extending as far as the cochlea itself. Earlier attempts to investigate the effects of attention on human cochlear processing have revealed small and inconsistent effects. In this study, stimulus-frequency otoacoustic emissions were recorded from a total of 30 human participants as they performed tasks that required sustained selective attention to auditory or visual stimuli. In the first sample of 15 participants, emission magnitudes were significantly weaker when participants attended to the visual stimuli than when they attended to the auditory stimuli, by an average of 5.4 dB. However, no such effect was found in the second sample of 15 participants. When the data were poole...

Significance Sound consists of a dynamic stream of energy at different frequencies. Auditory processing of sound frequency is critical in determining our ability to interact and communicate in a complex acoustic world, yet fundamental gaps remain in our understanding of how this is achieved. Indeed, the resolving power of the system, how best to measure it, and the mechanisms that underlie it are all still debated. Here, we provide critical evidence demonstrating that humans can resolve the frequency components of competing sounds better than other commonly studied mammals. This finding raises important questions both for theories of auditory perception and for our understanding of the evolutionary relationships between the auditory system and acoustic communication, including speech., Frequency analysis of sound by the cochlea is the most fundamental property of the auditory system. Despite its importance, the resolution of this frequency analysis in humans remains controversial. The controversy persists because the methods used to estimate tuning in humans are indirect and have not all been independently validated in other species. Some data suggest that human cochlear tuning is considerably sharper than that of laboratory animals, while others suggest little or no difference between species. We show here in a single species (ferret) that behavioral estimates of tuning bandwidths obtained using perceptual masking methods, and objective estimates obtained using otoacoustic emissions, both also employed in humans, agree closely with direct physiological measurements from single auditory-nerve fibers. Combined with human behavioral data, this outcome indicates that the frequency analysis performed by the human cochlea is of significantly higher resolution than found in common laboratory animals. This finding raises important questions about the evolutionary origins of human cochlear tuning, its role in the emergence of speech communication, and the mechanisms underlying our ability to separate and process natural sounds in complex acoustic environments.

Segregating and understanding speech in complex environments is a major challenge for hearing-impaired (HI) listeners. It remains unclear to what extent these difficulties are dominated by direct interference, such as simultaneous masking, or by a failure of the mechanisms of stream segregation. This study compared HI listeners’ performance with that of young and age-matched normal-hearing (NH) listeners in stream segregation tasks involving speech sounds. Listeners were presented with sequences of speech tokens, each consisting of a fricative consonant and a voiced vowel (CV). The CV tokens were concatenated into interleaved sequences that alternated in fundamental frequency (F0) and/or simulated vocal tract length (VTL). Each pair of interleaved sequences was preceded by a “word” consisting of two random tokens. The listeners were asked to indicate whether the word was present in the following interleaved sequences. The word, if present, occurred within one of the interleaved sequences, so that performance improved if the listeners were able to perceptually segregate the two sequences. Although HI listeners’ identification of the speech tokens in isolation was poorer than that of the NH listeners, HI listeners with both mild and moderate hearing loss were generally able to use both F0 and VTL cues to segregate the interleaved sequences. The results suggest that the difficulties experienced by HI listeners in complex acoustic environments cannot be explained by a loss of basic stream segregation abilities.

Auditory enhancement, where a target sound within a masker is rendered more audible by the prior presentation of the masker alone, may play an important role in auditory perception under variable everyday acoustic conditions. Cochlear hearing loss may reduce enhancement effects, potentially contributing to the difficulties experienced by hearing-impaired (HI) individuals in noisy and reverberant environments. However, it remains unknown whether, and by how much, enhancement under simultaneous masking is reduced in HI listeners. Enhancement of a pure tone under simultaneous masking with a multi-tone masker was measured in HI listeners and age-matched normal-hearing (NH) listeners as function of the spectral notch width of the masker, using stimuli at equal sensation levels as well as at equal sound pressure levels, but with the stimuli presented in noise to the NH listeners to maintain the equal sensation level between listener groups. The results showed that HI listeners exhibited some enhancement in all conditions. However, even when conditions were made as comparable as possible, in terms of effective spectral notch width and presentation level, the enhancement effect in HI listeners under simultaneous masking was reduced relative to that observed in NH listeners.

Timbre, or sound quality, is a crucial but poorly understood dimension of auditory perception that is important in describing speech, music, and environmental sounds. The present study investigates the cortical representation of different timbral dimensions. Encoding models have typically incorporated the physical characteristics of sounds as features when attempting to understand their neural representation with functional MRI. Here we test an encoding model that is based on five subjectively derived dimensions of timbre to predict cortical responses to natural orchestral sounds. Results show that this timbre model can outperform other models based on spectral characteristics, and can perform as well as a complex joint spectrotemporal modulation model. In cortical regions at the medial border of Heschl's gyrus, bilaterally, and regions at its posterior adjacency in the right hemisphere, the timbre model outperforms even the complex joint spectrotemporal modulation model. These findings suggest that the responses of cortical neuronal populations in auditory cortex may reflect the encoding of perceptual timbre dimensions.

Several studies have reported enhanced neural coding of stimulus periodicity (frequency following response; FFR) and/or shorter neural response latencies to speech sounds in musicians than in non-musicians. Such enhanced early encoding may underlie the reported musician advantage for perceiving speech in noise. If such perceptual benefits are confirmed, it is possible that musical training may be an effective intervention for offsetting the decline of this important skill with age. This presentation will review evidence for and against the musician advantage in the neural coding and perception of speech, and will highlight several reasons to be cautious of the generalizability of the musician advantage in the published literature, including (1) small sample sizes, (2) varying definitions of musician and non-musician, (3) dichotomous between-group comparisons (e.g., comparing professional musicians to non-musicians), (4) possible speech-corpus specific effects, and (5) the multitude of degrees of freedom in FFR analyses. Efforts towards large-sample replications that use open science techniques, including preregistered hypotheses, methods and analyses, as well as open source data, should bring clarity to the association between musical expertise and the neural coding and perception of speech in noise. [Work supported by NIH under Grant R01 DC005216 and NSF-BCS under Grant 1840818.]

Cochlea-scaled entropy (CSE) is a measure of spectro-temporal change that has been reported to predict the contribution of speech segments to overall intelligibility. This paper confirms that CSE is highly correlated with intensity, making it impossible to determine empirically whether it is CSE or simply intensity that determines speech importance. A more perceptually relevant version of CSE that uses dB-scaled differences, rather than differences in linear amplitude, failed to predict speech intelligibility. Overall, a parsimonious account of the available data is that the importance of speech segments to overall intelligibility is best predicted by their relative intensity, not by CSE.

Differences in spatial cues, including interaural time differences (ITDs), interaural level differences (ILDs) and spectral cues, can lead to stream segregation of alternating noise bursts. It is unknown how effective such cues are for streaming sounds with realistic spectro-temporal variations. In particular, it is not known whether the high-frequency spectral cues associated with elevation remain sufficiently robust under such conditions. To answer these questions, sequences of consonant-vowel tokens were generated and filtered by non-individualized head-related transfer functions to simulate the cues associated with different positions in the horizontal and median planes. A discrimination task showed that listeners could discriminate changes in interaural cues both when the stimulus remained constant and when it varied between presentations. However, discrimination of changes in spectral cues was much poorer in the presence of stimulus variability. A streaming task, based on the detection of repeated syllables in the presence of interfering syllables, revealed that listeners can use both interaural and spectral cues to segregate alternating syllable sequences, despite the large spectro-temporal differences between stimuli. However, only the full complement of spatial cues (ILDs, ITDs, and spectral cues) resulted in obligatory streaming in a task that encouraged listeners to integrate the tokens into a single stream.

Congenital amusia is a music perception disorder believed to reflect a deficit in fine-grained pitch perception and/or short-term or working memory for pitch. Because most measures of pitch perception include memory and segmentation components, it has been difficult to determine the true extent of pitch processing deficits in amusia. It is also unclear whether pitch deficits persist at frequencies beyond the range of musical pitch. To address these questions, experiments were conducted with amusics and matched controls, manipulating both the stimuli and the task demands. First, we assessed pitch discrimination at low (500 Hz and 2000 Hz) and high (8000 Hz) frequencies using a three-interval forced-choice task. Amusics exhibited deficits even at the highest frequency, which lies beyond the existence region of musical pitch. Next, we assessed the extent to which frequency coding deficits persist in one- and two-interval frequency-modulation (FM) and amplitude-modulation (AM) detection tasks at 500 Hz at slow (fm = 4 Hz) and fast (fm = 20 Hz) modulation rates. Amusics still exhibited deficits in one-interval FM detection tasks that should not involve memory or segmentation. Surprisingly, amusics were also impaired on AM detection, which should not involve pitch processing. Finally, direct comparisons between the detection of continuous and discrete FM demonstrated that amusics suffer deficits both in coding and segmenting pitch information. Our results reveal auditory deficits in amusia extending beyond pitch perception that are subtle when controlling for memory and segmentation, and are likely exacerbated in more complex contexts such as musical listening.

Natural sounds can be characterized by their fluctuations in amplitude and frequency. Ageing may affect sensitivity to some forms of fluctuations more than others. The present study used individual differences across a wide age range (20–79 years) to test the hypothesis that slow-rate, low-carrier frequency modulation (FM) is coded by phase-locked auditory-nerve responses to temporal fine structure (TFS), whereas fast-rate FM is coded via rate-place (tonotopic) cues, based on amplitude modulation (AM) of the temporal envelope after cochlear filtering. Using a low (500 Hz) carrier frequency, diotic FM and AM detection thresholds were measured at slow (1 Hz) and fast (20 Hz) rates in 85 listeners. Frequency selectivity and TFS coding were assessed using forward masking patterns and interaural phase disparity tasks (slow dichotic FM), respectively. Comparable interaural level disparity tasks (slow and fast dichotic AM and fast dichotic FM) were measured to control for effects of binaural processing not specifically related to TFS coding. Thresholds in FM and AM tasks were correlated, even across tasks thought to use separate peripheral codes. Age was correlated with slow and fast FM thresholds in both diotic and dichotic conditions. The relationship between age and AM thresholds was generally not significant. Once accounting for AM sensitivity, only diotic slow-rate FM thresholds remained significantly correlated with age. Overall, results indicate stronger effects of age on FM than AM. However, because of similar effects for both slow and fast FM when not accounting for AM sensitivity, the effects cannot be unambiguously ascribed to TFS coding.

A target within a spectrally notched masker can be enhanced by a preceding copy of the masker. Enhancement can also increase the effectiveness of the target as a forward masker. Enhancement has been reported in hearing-impaired listeners under simultaneous but not forward masking. However, previous studies of enhancement under forward masking did not fully assess the potential effect of differences in sensation level or spectral resolution between the normal-hearing and hearing-impaired listeners. This study measured enhancement via forward masking in hearing-impaired and age-matched normal-hearing listeners with different spectral notches in the masker, to account for potential differences in frequency selectivity, and with levels equated by adding a background masking noise to equate both sensation level and sound pressure level or by reducing the sound pressure level of the stimuli to equate sensation level. Hearing-impaired listeners showed no significant enhancement, regardless of spectral notch width. Normal-hearing listeners showed enhancement at high levels, but showed less enhancement when sensation levels were reduced to match those of the hearing-impaired group, either by reducing sound levels or by adding a masking noise. The results confirm a lack of forward-masked enhancement in hearing-impaired listeners but suggest this may be partly due to reduced sensation level.

A rapid forward-masked spatial tuning curve measurement procedure, based on Bekesy tracking, was adapted and evaluated for use with cochlear implants. Twelve postlingually-deafened adult cochlear-implant users participated. Spatial tuning curves using the new procedure and using a traditional forced-choice adaptive procedure resulted in similar estimates of parameters. The Bekesy-tracking method was almost 3 times faster than the forced-choice procedure, but its test–retest reliability was significantly poorer. Although too time-consuming for general clinical use, the new method may have some benefits in individual cases, where identifying electrodes with poor spatial selectivity as candidates for deactivation is deemed necessary.

Recent physiological studies of basilar rnembrane (BM) mechanics indicate that the response to tones presented at the characteristic frequency (CF) is nonlinear and cornpressive. Input-output functions show marked compression at medium input levels and become more linear at very low and very high levels. Damage to the cochlea, in particular the outer hair celis, generally results in a loss of sensitivity and a linearization of the BM transfer function. In this study we assume that listeners with cochlear hearing loss also exhibit reduced BM compression, and we investigate some possible psychoacoustic consequences of the reduced nonlinearity. Results from nonsimultaneous rnasking experiments in norrnally hearing listeners were modeled using a temporal window model, preceded by a compressive nonlinearity (Oxenham & Moore, 1994). When modeling sirnilar data from hearing-impaired listeners, only the input nonlinearity of the model was changed. The results suggest that the change in nonlinearity may be sufficient to account for some differences in performance in the additivity of nonsimultaneous masking, the decay of forward masking with increasing masker-signal interval, and the growth of forward masking with increasing masker level.