Evidence that the Lombard effect is frequency-specific in humans

Noises on-How the Brain Deals with Acoustic Noise

What is noise? When does a sound form part of the acoustic background and when might it come to our attention as part of the foreground? Our brain seems to filter out irrelevant sounds in a seemingly effortless process, but how this is achieved remains opaque and, to date, unparalleled by any algorithm. In this review, we discuss how noise can be both background and foreground, depending on what a listener/brain is trying to achieve. We do so by addressing questions concerning the brain's potential bias to interpret certain sounds as part of the background, the extent to which the interpretation of sounds depends on the context in which they are heard, as well as their ethological relevance, task-dependence, and a listener's overall mental state. We explore these questions with specific regard to the implicit, or statistical, learning of sounds and the role of feedback loops between cortical and subcortical auditory structures.

Work-Related Vocal Challenges of Online Teaching: A Study of Female College Professors

BACKGROUND

College professors are at an elevated risk of developing voice disorders due to increased vocal demands associated with their working conditions, including high background noise levels, long reverberation times, prolonged voice use duration, and large class sizes. However, the impact of online classes on vocal health among college professors remains unclear.

OBJECTIVE

This longitudinal study aimed to characterize voice changes associated with online teaching among female Colombian college professors.

METHODS

Thirteen female college professors teaching online classes completed an online survey that included questions about voice functioning, working conditions, the Spanish translation of the Vocal Fatigue Index (VFI), and the Spanish translation of the Voice-Related Quality of Life. Instrumental measurements were also performed, including environmental background noise levels, hearing screening, and voice recordings before and after a synchronous online class.

RESULTS

This study found a decreased fundamental frequency in connected speech (reading) associated with the number of students per class, the number of classes per week, and background noise levels measured with a sound level meter. L1L0 was statistically smaller among experienced teachers with higher background noise levels compared with less-experienced colleagues in quieter classes. 1558kHz was statistically associated with the average number of students, whereas HNR was slightly higher for professors with more students and more classes per week.

CONCLUSION

The findings suggest that online teaching has important implications for voice production among participating teachers. This study highlights the importance of considering working conditions during online classes when designing workplace prevention programs for college professors.

Marmoset monkeys use different avoidance strategies to cope with ambient noise during vocal behavior

Multiple strategies have evolved to compensate for masking noise, leading to changes in call features. One call adjustment is the Lombard effect, an increase in call amplitude in response to noise. Another strategy involves call production in periods where noise is absent. While mechanisms underlying vocal adjustments have been well studied, mechanisms underlying noise avoidance strategies remain largely unclear. We systematically perturbed ongoing phee calls of marmosets to investigate noise avoidance strategies. Marmosets canceled their calls after noise onset and produced longer calls after noise-phases ended. Additionally, the number of uttered syllables decreased during noise perturbation. This behavior persisted beyond the noise-phase. Using machine learning techniques, we found that a fraction of single phees were initially planned as double phees and became interrupted after the first syllable. Our findings indicate that marmosets use different noise avoidance strategies and suggest vocal flexibility at different complexity levels in the marmoset brain.

Design and Development of a Spanish Hearing Test for Speech in Noise (PAHRE)

BACKGROUND

There are few hearing tests in Spanish that assess speech discrimination in noise in the adult population that take into account the Lombard effect. This study presents the design and development of a Spanish hearing test for speech in noise (Prueba Auditiva de Habla en Ruido en Español (PAHRE) in Spanish). The pattern of the Quick Speech in Noise test was followed when drafting sentences with five key words each grouped in lists of six sentences. It was necessary to take into account the differences between English and Spanish.

METHODS

A total of 61 people (24 men and 37 women) with an average age of 46.9 (range 18-84 years) participated in the study. The work was carried out in two phases. In the first phase, a list of Spanish sentences was drafted and subjected to a familiarity test based on the semantic and syntactic characteristics of the sentences; as a result, a list of sentences was selected for the final test. In the second phase, the selected sentences were recorded with and without the Lombard effect, the equivalence between both lists was analysed, and the test was applied to a first reference population.

RESULTS

The results obtained allow us to affirm that it is representative of the Spanish spoken in its variety in peninsular Spain.

CONCLUSIONS

In addition, these results point to the usefulness of the PAHRE test in assessing speech in noise by maintaining a fixed speech intensity while varying the intensity of the multi-speaker background noise. The incorporation of the Lombard effect in the test shows discrimination differences with the same signal-to-noise ratio compared to the test without the Lombard effect.

Lombard Effect in Individuals With Nonphonotraumatic Vocal Hyperfunction: Impact on Acoustic, Aerodynamic, and Vocal Fold Vibratory Parameters

PURPOSE

This exploratory study aims to investigate variations in voice production in the presence of background noise (Lombard effect) in individuals with nonphonotraumatic vocal hyperfunction (NPVH) and individuals with typical voices using acoustic, aerodynamic, and vocal fold vibratory measures of phonatory function.

METHOD

Nineteen participants with NPVH and 19 participants with typical voices produced simple vocal tasks in three sequential background conditions: baseline (in quiet), Lombard (in noise), and recovery (5 min after removing the noise). The Lombard condition consisted of speech-shaped noise at 80 dB SPL through audiometric headphones. Acoustic measures from a microphone, glottal aerodynamic parameters estimated from the oral airflow measured with a circumferentially vented pneumotachograph mask, and vocal fold vibratory parameters from high-speed videoendoscopy were analyzed.

RESULTS

During the Lombard condition, both groups exhibited a decrease in open quotient and increases in sound pressure level, peak-to-peak glottal airflow, maximum flow declination rate, and subglottal pressure. During the recovery condition, the acoustic and aerodynamic measures of individuals with typical voices returned to those of the baseline condition; however, recovery measures for individuals with NPVH did not return to baseline values.

CONCLUSIONS

As expected, individuals with NPVH and participants with typical voices exhibited a Lombard effect in the presence of elevated background noise levels. During the recovery condition, individuals with NPVH did not return to their baseline state, pointing to a persistence of the Lombard effect after noise removal. This behavior could be related to disruptions in laryngeal motor control and may play a role in the etiology of NPVH.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.20415600.

The effects of Lombard perturbation on speech intelligibility in noise for normal hearing and cochlear implant listeners

Natural compensation of speech production in challenging listening environments is referred to as the Lombard effect (LE). The resulting acoustic differences between neutral and Lombard speech have been shown to provide intelligibility benefits for normal hearing (NH) and cochlear implant (CI) listeners alike. Motivated by this outcome, three LE perturbation approaches consisting of pitch, duration, formant, intensity, and spectral contour modifications were designed specifically for CI listeners to combat speech-in-noise performance deficits. Experiment 1 analyzed the effects of loudness, quality, and distortion of approaches on speech intelligibility with and without formant-shifting. Significant improvements of +9.4% were observed in CI listeners without the formant-shifting approach at +5 dB signal-to-noise ratio (SNR) large-crowd-noise (LCN) when loudness was controlled, however, performance was found to be significantly lower for NH listeners. Experiment 2 evaluated the non-formant-shifting approach with additional spectral contour and high pass filtering to reduce spectral smearing and decrease distortion observed in Experiment 1. This resulted in significant intelligibility benefits of +30.2% for NH and +21.2% for CI listeners at 0 and +5 dB SNR LCN, respectively. These results suggest that LE perturbation may be useful as front-end speech modification approaches to improve intelligibility for CI users in noise.

Non-stereotyped amplitude modulation across signature whistle contours

Bottlenose dolphin signature whistles are characterized by distinctive frequency modulation over time. The stable frequency contours of these whistles broadcast individual identity information. Little is known however, about whether or not the amplitude contour is also stereotyped. Here, we examined the relative amplitude-time contour of signature whistle emissions from eight bottlenose dolphins (Tursiops truncatus) in the U.S. Navy Marine Mammal Program (MMP) in San Diego, CA. The results suggested that unlike the stable frequency-time contour, the amplitude-time contour of signature whistles were largely non-stereotyped, characterized by large variability across multiple whistle emissions. Relative amplitude was negatively related to log peak frequency, with more energy focused in the lower frequency bands. This trend was consistent over all eight dolphins despite having quite different signature whistle contours. This relationship led to the amplitude contours being slightly more stereotyped within than between dolphins. We propose that amplitude across signature whistle emissions may serve as an avenue for encoding additional communicative information. We encourage future studies to incorporate analyses of amplitude contours in addition to frequency contours of signature whistles in order to begin to understand what role it may play in the dolphin communication system.

Acoustic Sensing Analytics Applied to Speech in Reverberation Conditions

The paper aims to discuss a case study of sensing analytics and technology in acoustics when applied to reverberation conditions. Reverberation is one of the issues that makes speech in indoor spaces challenging to understand. This problem is particularly critical in large spaces with few absorbing or diffusing surfaces. One of the natural remedies to improve speech intelligibility in such conditions may be achieved through speaking slowly. It is possible to use algorithms that reduce the rate of speech (RoS) in real time. Therefore, the study aims to find recommended values of RoS in the context of STI (speech transmission index) in different acoustic environments. In the experiments, speech intelligibility for six impulse responses recorded in spaces with different STIs is investigated using a sentence test (for the Polish language). Fifteen subjects with normal hearing participated in these tests. The results of the analytical analysis enabled us to propose a curve specifying the maximum RoS values translating into understandable speech under given acoustic conditions. This curve can be used in speech processing control technology as well as compressive reverse acoustic sensing.

Impact of Noise in Operating Theater: A Surgeon's and Anesthesiologist's Perspective

Background and Aims

Noise is often considered as an undesirable sound. Excess noise is a health threat that deteriorates one's concentration and communication. Noise in the operating theater can be disturbing, impairs communication, and can lead to stress. The aim of this survey was to assimilate information about the perspective of surgeons and anesthesiologists regarding noise in the operating theater and whether it affects their work atmosphere.

Methods

A questionnaire consisting of 15 closed-ended questions excluding one open-ended question was given to surgeons from various specialties and anesthesiologists. The subjective response were analyzed and documented. Data analysis was done using descriptive statistics. Association was found out using Chi-square test.

Results

We collected a total of 290 responses, of which 87.6% (n = 254) considered noise to increase the stress level and deteriorates the quality of teamwork (83.8%, n = 243). Noise affects communication among the staff (86.2%, n = 250) and decreases their concentration level (85.5%, n = 248) which could be harmful in view of the patient's safety. 87.9% (n = 255) of the participants were in favor of limiting the number of people in the operating theater. Nonetheless, 73% (n = 211) considered music has a calming effect and were in favor of music in the operating theater.

Conclusion

Noise in the operating theater can have distressing effects on surgeons, jeopardizing the patient's safety. However, a flip side to this is that music is considered to have a calming and soothing effect decreasing the anxiety and stress levels.

The Perception and Attitude Toward Noise and Music in the Operating Room: A Systematic Review

BACKGROUND

Environmental noise pollution is regarded as a general stressor. Noise levels frequently exceed recommended noise levels by the World Health Organization in hospitals, especially in the operation room. The aim of this systematic review was to assess the effects of noise pollution on patient outcome and performance by operation room staff. In addition, the perception and attitude toward playing music in the operation room, which can increase noise levels, were assessed as well.

MATERIALS AND METHODS

A systematic literature search of the databases Embase, Medline Ovid, and Cochrane from date of database inception until October 16^th, 2020 using the exhaustive literature search method was performed. Prospective studies evaluating the effect of noise on the patient, surgeons, anesthesiologists, nurses, and other operation room staff, or perception and attitude toward playing music in the operation room, were included. This systematic review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines and was registered with PROSPERO (ID: 208282).

RESULTS

The literature search generated 4758 articles, and 22 prospective studies (3507 participants) were included. Three of the four studies that investigated the effect of noise on patient outcome reported a significant reduction of complication rate in surgical patients, when noise levels were lower. Six studies assessed the effect of noise in the operation room on the staff (1383 participants). Over half of the surveyed staff found noise levels to be a disturbing stressor and negatively impact performance. Although music increased decibel levels in the operation room, most surveyed staff was positively predisposed toward playing music during surgery, believing it to improve both individual and team performance. In general, music was not considered to be distracting or impairing communication.

CONCLUSIONS

Higher noise levels seem to have a negative effect on patient outcome and adversely affect performance by members in the operation room. Further research is needed to assess whether this knowledge can benefit patient outcome and surgical performance. Notably, attitude of surgical team members toward music during surgery is generally regarded favorable.

Effects of task and language nativeness on the Lombard effect and on its onset and offset timing

This study focuses on the differences in speech sound pressure levels (here, called speech loudness) of Lombard speech (i.e., speech produced in the presence of an energetic masker) associated with different tasks and language nativeness. Vocalizations were produced by native speakers of Japanese with normal hearing and limited English proficiency while performing four tasks: dialog, a competitive game (both communicative), soliloquy, and text passage reading (noncommunicative). Relative to the native language (L1), larger loudness increments were observed in the game and text reading when performed in the second language (L2). Communicative tasks yielded louder vocalizations and larger increments of speech loudness than did noncommunicative tasks regardless of the spoken language. The period in which speakers increased their loudness after the onset of the masker was about fourfold longer than the time in which they decreased their loudness after the offset of the masker. Results suggest that when relying on acoustic signals, speakers use similar vocalization strategies in L1 and L2, and these depend on the complexity of the task, the need for accurate pronunciation, and the presence of a listener. Results also suggest that speakers use different strategies depending on the onset or offset of an energetic masker.

Neural Correlates of Vocal Auditory Feedback Processing: Unique Insights from Electrocorticography Recordings in a Human Cochlear Implant User

There is considerable interest in understanding cortical processing and the function of top-down and bottom-up human neural circuits that control speech production. Research efforts to investigate these circuits are aided by analysis of spectro-temporal response characteristics of neural activity recorded by electrocorticography (ECoG). Further, cortical processing may be altered in the case of hearing-impaired cochlear implant (CI) users, as electric excitation of the auditory nerve creates a markedly different neural code for speech compared with that of the functionally intact hearing system. Studies of cortical activity in CI users typically record scalp potentials and are hampered by stimulus artifact contamination and by spatiotemporal filtering imposed by the skull. We present a unique case of a CI user who required direct recordings from the cortical surface using subdural electrodes implanted for epilepsy assessment. Using experimental conditions where the subject vocalized in the presence (CIs ON) or absence (CIs OFF) of auditory feedback, or listened to playback of self-vocalizations without production, we observed ECoG activity primarily in γ (32–70 Hz) and high γ (70–150 Hz) bands at focal regions on the lateral surface of the superior temporal gyrus (STG). High γ band responses differed in their amplitudes across conditions and cortical sites, possibly reflecting different rates of stimulus presentation and differing levels of neural adaptation. STG γ responses to playback and vocalization with auditory feedback were not different from responses to vocalization without feedback, indicating this activity reflects not only auditory, but also attentional, efference-copy, and sensorimotor processing during speech production.

Echolocating bats exhibit differential amplitude compensation for noise interference at a sub-call level

Flexible vocal production control enables sound communication in both favorable and unfavorable conditions. The Lombard effect, which describes a rise in call amplitude with increasing ambient noise, is a widely exploited strategy by vertebrates to cope with interfering noise. In humans, the Lombard effect influences the lexical stress through differential amplitude modulation at a sub-call syllable level, which so far has not been documented in animals. Here, we bridge this knowledge gap with two species of Hipposideros bats, which produce echolocation calls consisting of two functionally well-defined units: the constant-frequency (CF) and frequency-modulated (FM) components. We show that ambient noise induced a strong, but differential, Lombard effect in the CF and FM components of the echolocation calls. We further report that the differential amplitude compensation occurred only in the spectrally overlapping noise conditions, suggesting a functional role in releasing masking. Lastly, we show that both species of bats exhibited a robust Lombard effect in the spectrally non-overlapping noise conditions, which contrasts sharply with the existing evidence. Our data highlight echolocating bats as a potential mammalian model for understanding vocal production control.

Vowel and Sibilant Production in Noise: Effects of Noise Frequency and Phonological Similarity

Purpose This study investigated vowel and sibilant productions in noise to determine whether responses to noise (a) are sensitive to the spectral characteristics of the noise signal and (b) are modulated by the contribution of vowel or sibilant contrasts to word discrimination. Method Vowel and sibilant productions were elicited during serial recall of three-word sequences that were produced in quiet or during exposure to speaker-specific noise signals. These signals either masked a speaker's productions of the sibilants /s/ and /ʃ/ or their productions of the vowels /a/ and /æ/. The contribution of the vowel and sibilant contrasts to word discrimination in a sequence was manipulated by varying the number of times that the target sibilant and vowel pairs occurred in the same word position in each sequence. Results Spectral noise effects were observed for both sibilants and vowels: Responses to noise were larger and/or involved to more acoustic features when the noise signal masked the acoustic characteristics of that phoneme class. Word discrimination effects were limited and consisted of only small increases in vowel duration. Interaction effects between noise and similarity indicated that the phonological similarity of sequences containing both sibilants and/or both vowels influenced articulation in ways not related to speech clarity. Conclusion The findings of this study indicate that sensorimotor control of speech exhibits some sensitivity to noise spectral characteristics. However, productions of sibilants and vowels were not sensitive to their importance in discriminating the words in a sequence. In addition, phonological similarity effects were observed that likely reflected processing demands related to the recall and sequencing of high-similarity words.

Auralization uses in acoustical design: A survey study of acoustical consultants

While auralization technology is used in a variety of fields, particularly in architectural acoustics, there is a lack of data on the auralization tools used and actual practices. In this perspective, this work presents the results of a survey study on auralization uses in the acoustical design and consulting community, targeting acoustical consultants. The objectives are (1) to identify the tools and methods used by acousticians to create auralizations as well as effective uses so as to understand the benefits and changes provided by this technology, and (2) to highlight the difficulties and limitations linked to the use of auralizations in concrete projects. Based on the theory of acceptability and use of technology, the study was conducted from a mix of quantitative and qualitative data collection approaches, combining a questionnaire answered by 74 respondents with semi-directed interviews with nine practitioners. Results highlight the main uses of auralizations, the diversity of projects in which auralizations are applied, and how auralizations are currently used in real-world situations. The benefits of using this technology, inherent weaknesses in the tools, and practical difficulties are also discussed.

Vocal Biomarkers of Mild-to-Moderate Hearing Loss in Children and Adults: Voiceless Sibilants

PURPOSE

The purpose of this study was to determine if an objective measure of speech production could serve as a vocal biomarker for the effects of high-frequency hearing loss on speech perception. It was hypothesized that production of voiceless sibilants is governed sufficiently by auditory feedback that high-frequency hearing loss results in subtle but significant shifts in the spectral characteristics of these sibilants.

METHOD

Sibilant production was examined in individuals with mild to moderately severe congenital (22 children; 8-17 years old) and acquired (23 adults; 55-80 years old) hearing losses. Measures of hearing level (pure-tone average thresholds at 4 and 8 kHz), speech perception (detection of nonsense words within sentences), and speech production (spectral center of gravity [COG] for /s/ and /ʃ/) were obtained in unaided and aided conditions.

RESULTS

For both children and adults, detection of nonsense words increased significantly as hearing thresholds improved. Spectral COG for /ʃ/ was unaffected by hearing loss in both listening conditions, whereas the spectral COG for /s/ significantly decreased as high-frequency hearing loss increased. The distance in spectral COG between /s/ and /ʃ/ decreased significantly with increasing hearing level. COG distance significantly predicted nonsense-word detection in children but not in adults.

CONCLUSIONS

At least one aspect of speech production (voiceless sibilants) is measurably affected by high-frequency hearing loss and is related to speech perception in children. Speech production did not predict speech perception in adults, suggesting a more complex relationship between auditory feedback and feedforward mechanisms with age. Even so, these results suggest that this vocal biomarker may be useful for identifying the presence of high-frequency hearing loss in adults and children and for predicting the impact of hearing loss in children.

The function and mechanism of vocal accommodation in humans and other primates

The study of non-human animals, in particular primates, can provide essential insights into language evolution. A critical element of language is vocal production learning, i.e. learning how to produce calls. In contrast to other lineages such as songbirds, vocal production learning of completely new signals is strikingly rare in non-human primates. An increasing body of research, however, suggests that various species of non-human primates engage in vocal accommodation and adjust the structure of their calls in response to environmental noise or conspecific vocalizations. To date it is unclear what role vocal accommodation may have played in language evolution, in particular because it summarizes a variety of heterogeneous phenomena which are potentially achieved by different mechanisms. In contrast to non-human primates, accommodation research in humans has a long tradition in psychology and linguistics. Based on theoretical models from these research traditions, we provide a new framework which allows comparing instances of accommodation across species, and studying them according to their underlying mechanism and ultimate biological function. We found that at the mechanistic level, many cases of accommodation can be explained with an automatic perception-production link, but some instances arguably require higher levels of vocal control. Functionally, both human and non-human primates use social accommodation to signal social closeness or social distance to a partner or social group. Together, this indicates that not only some vocal control, but also the communicative function of vocal accommodation to signal social closeness and distance must have evolved prior to the emergence of language, rather than being the result of it. Vocal accommodation as found in other primates has thus endowed our ancestors with pre-adaptations that may have paved the way for language evolution.

Effects of background noise on acoustic characteristics of Bengalese finch songs

Online regulation of vocalization in response to auditory feedback is one of the essential issues for vocal communication. One such audio-vocal interaction is the Lombard effect, an involuntary increase in vocal amplitude in response to the presence of background noise. Along with vocal amplitude, other acoustic characteristics, including fundamental frequency (F0), also change in some species. Bengalese finches (Lonchura striata var. domestica) are a suitable model for comparative, ethological, and neuroscientific studies on audio-vocal interaction because they require real-time auditory feedback of their own songs to maintain normal singing. Here, the changes in amplitude and F0 with a focus on the distinct song elements (i.e., notes) of Bengalese finches under noise presentation are demonstrated. To accurately analyze these acoustic characteristics, two different bandpass-filtered noises at two levels of sound intensity were used. The results confirmed that the Lombard effect occurs at the note level of Bengalese finch song. Further, individually specific modes of changes in F0 are shown. These behavioral changes suggested the vocal control mechanisms on which the auditory feedback is based have a predictable effect on amplitude, but complex spectral effects on individual note production.

Moderate evidence for a Lombard effect in a phylogenetically basal primate

When exposed to enhanced background noise, humans avoid signal masking by increasing the amplitude of the voice, a phenomenon termed the Lombard effect. This auditory feedback-mediated voice control has also been found in monkeys, bats, cetaceans, fish and some frogs and birds. We studied the Lombard effect for the first time in a phylogenetically basal primate, the grey mouse lemur, Microcebus murinus. When background noise was increased, mouse lemurs were able to raise the amplitude of the voice, comparable to monkeys, but they did not show this effect consistently across context/individuals. The Lombard effect, even if representing a generic vocal communication system property of mammals, may thus be affected by more complex mechanisms. The present findings emphasize an effect of context, and individual, and the need for further standardized approaches to disentangle the multiple system properties of mammalian vocal communication, important for understanding the evolution of the unique human faculty of speech and language.

Classroom Noise and Teachers' Voice Production

PURPOSE

The aim of this study was to research the associations between noise (ambient and activity noise) and objective metrics of teachers' voices in real working environments (i.e., classrooms).

METHOD

Thirty-two female and 8 male teachers from 14 elementary schools were randomly selected for the study. Ambient noise was measured during breaks in unoccupied classrooms and, likewise, the noise caused by pupils' activity during lessons. Voice samples were recorded before and after a working day. Voice variables measured were sound pressure level (voice SPL), fundamental frequency, jitter, shimmer, and the tilt of the sound spectrum slope (alpha ratio).

RESULTS

The ambient noise correlated most often with the fundamental frequency of men and voice SPL, whereas activity noise correlated with the alpha ratio and perturbation values. Teachers working in louder ambient noise spoke more loudly before work than those working in lower noise levels. Voice variables generally changed less during work among teachers working in loud activity noise than among those working in lower noise levels.

CONCLUSIONS

Ambient and activity noises affect teachers' voice use. Under loud ambient noise teachers seem to speak habitually loudly, and under loud activity noise teachers' ability to react to loading deteriorates.

Noise-Induced Frequency Modifications of Tamarin Vocalizations: Implications for Noise Compensation in Nonhuman Primates

Previous research suggests that nonhuman primates have limited flexibility in the frequency content of their vocalizations, particularly when compared to human speech. Consistent with this notion, several nonhuman primate species have demonstrated noise-induced changes in call amplitude and duration, with no evidence of changes to spectral content. This experiment used broad- and narrow-band noise playbacks to investigate the vocal control of two call types produced by cotton-top tamarins (Saguinus Oedipus). In 'combination long calls' (CLCs), peak fundamental frequency and the distribution of energy between low and high frequency harmonics (spectral tilt) changed in response to increased noise amplitude and bandwidth. In chirps, peak and maximum components of the fundamental frequency increased with increasing noise level, with no changes to spectral tilt. Other modifications included the Lombard effect and increases in chirp duration. These results provide the first evidence for noise-induced frequency changes in nonhuman primate vocalizations and suggest that future investigations of vocal plasticity in primates should include spectral parameters.