Natural Vocalizations Research Articles

Forming auditory objects in a reverberant cocktail party setting

Event Abstract Back to Event Forming auditory objects in a reverberant cocktail party setting Sandra H. Blumenrath1* and Robert J. Dooling1 1 University of Maryland, College Park, United States In multi-signaler environments, listeners are faced with the challenge to selectively attend to and follow sound sequences of one sender while disregarding those of others. As a solution to the so-called “Cocktail Party” problem, the auditory system has to group sound components from one source into a single object based on specific unifying physical features, while at the same time separating them from components from other sources with different unifying features. Some of the grouping cues are common onset and offset times, common amplitude modulations, as well as similar frequency ranges and spatial origins. Although the integration and segregation of auditory objects is aided by such cues, successful object formation may be compromised in natural environments where vocal signals are reverberated. In a cacophony of reverberated stimuli, tails of echoes and the interaction between direct and reflected sound waves can, for instance, obliterate sharp onset and offset times and alter both the temporal and spectral patterns of sounds. The goal of this study was to investigate the effect of reverberation on behavioral measures of auditory object formation under conditions with increasing numbers of simultaneous signalers. We designed a psychophysical experiment with budgerigars, canaries, and zebra finches, in which subjects were tested with natural vocalizations from all three species. Tests involved a GO/NOGO procedure, in which the birds had to keep responding throughout one of two previously learned, 4-s long song sequences (GO vs. NOGO song) either in the absence (control) or presence of other superimposed songs from one, two, or four different individuals. The GO and NO GO song differed only towards the end, which forced the birds to attend to the entire song sequence. In the case of a NOGO song the birds would stop responding towards the end. A complete object was formed if correct responses (GO or NOGO) were given to either of these two sequence. Results showed clear independent effects of reverberation time, number of simultaneously singing individuals, and vocalization type. Most importantly, the birds’ ability to selectively attend to a specific sequence of sounds was particularly compromised when very high reverberation times coincided with many birds singing in the background, indicating a synergistic effect between the two factors. In contrast, neither of these factors alone decreased the birds’ sensitivity to or below threshold. Budgerigars generally outperformed both canaries and zebra finches and also showed a clear advantage when tested with conspecific song. These results revealed that in a cocktail party environment with multiple signalers, sound reverberation plays a critical role in affecting the percept of distinct auditory objects and renders identification of individual sound sources more difficult. The degree to which auditory stream segregation is compromised, however, depends on the amount of reverberation as well as the number of signaling individuals. Keywords: auditory object formation, auditory scene analysis, bird vocalizations, Birds, environmental acoustics, Psychoacoustics, reverberation Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster Presentation (see alternatives below as well) Topic: Sensory: Audition Citation: Blumenrath SH and Dooling RJ (2012). Forming auditory objects in a reverberant cocktail party setting. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00061 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 08 May 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Sandra H Blumenrath, University of Maryland, College Park, College Park, MD, 20742, United States, shb@umd.edu Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Sandra H Blumenrath Robert J Dooling Google Sandra H Blumenrath Robert J Dooling Google Scholar Sandra H Blumenrath Robert J Dooling PubMed Sandra H Blumenrath Robert J Dooling Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Condition-dependent auditory processing in the round goby (Neogobius melanostomus): links to sex, reproductive condition, and female estrogen levels.

Neural responses to sensory stimuli often differ between sexes, vary seasonally, and can be regulated by endocrine activity, but the ecological and physiological mechanisms driving such patterns are not well understood. The current study examined how auditory function in the round goby (Neogobius melanostomus), a vocal teleost, co-varied with sex, reproductive condition and female plasma 17β-estradiol level. Auditory evoked potentials were collected in response to tone pips (100-600 Hz) and a natural round goby pulse vocalization. Additionally, saccule hair cell densities were compared across reproductive groups. Auditory threshold was evaluated in terms of pressure and particle acceleration, and response amplitude and onset latency were measured at 10 dB above threshold. Relative to males, females displayed lower auditory thresholds in response to the natural vocalization and to tones at 300-600 Hz, and had a higher density of saccule hair cells. The 17β-estradiol level was positively associated with amplitude and latency for the pulse stimulus and with both threshold and amplitude for tones at 100-200 Hz in females. Relative to non-reproductive males, reproductive males exhibited longer response latencies at 100-200 Hz. The results demonstrate sexual dimorphism in auditory function in a teleost fish as well as intra-sexual variation, partially based on hormone levels. The current research further identifies links between auditory function and reproductive behaviors in fishes and provides a finer-scaled analysis of how this behavior is reflected at the level of the sensory systems facilitating signal reception.

Rhythmic synchronization tapping to an audio–visual metronome in budgerigars

In all ages and countries, music and dance have constituted a central part in human culture and communication. Recently, vocal-learning animals such as parrots and elephants have been found to share rhythmic ability with humans. Thus, we investigated the rhythmic synchronization of budgerigars, a vocal-mimicking parrot species, under controlled conditions and a systematically designed experimental paradigm as a first step in understanding the evolution of musical entrainment. We trained eight budgerigars to perform isochronous tapping tasks in which they pecked a key to the rhythm of audio–visual metronome-like stimuli. The budgerigars showed evidence of entrainment to external stimuli over a wide range of tempos. They seemed to be inherently inclined to tap at fast tempos, which have a similar time scale to the rhythm of budgerigars' natural vocalizations. We suggest that vocal learning might have contributed to their performance, which resembled that of humans.

Seasonal plasticity of auditory hair cell frequency sensitivity correlates with plasma steroid levels in vocal fish.

Vertebrates displaying seasonal shifts in reproductive behavior provide the opportunity to investigate bidirectional plasticity in sensory function. The midshipman teleost fish exhibits steroid-dependent plasticity in frequency encoding by eighth nerve auditory afferents. In this study, evoked potentials were recorded in vivo from the saccule, the main auditory division of the inner ear of most teleosts, to test the hypothesis that males and females exhibit seasonal changes in hair cell physiology in relation to seasonal changes in plasma levels of steroids. Thresholds across the predominant frequency range of natural vocalizations were significantly less in both sexes in reproductive compared with non-reproductive conditions, with differences greatest at frequencies corresponding to call upper harmonics. A subset of non-reproductive males exhibiting an intermediate saccular phenotype had elevated testosterone levels, supporting the hypothesis that rising steroid levels induce non-reproductive to reproductive transitions in saccular physiology. We propose that elevated levels of steroids act via long-term (days to weeks) signaling pathways to upregulate ion channel expression generating higher resonant frequencies characteristic of non-mammalian auditory hair cells, thereby lowering acoustic thresholds.

Non‐Selective and Time‐Dependent Behavioural Responses of Common Toads (Bufo bufo) to Predator Acoustic Cues

AbstractAcoustic predator recognition has rarely been studied in anurans, in spite of the fact that hearing is widespread in these animals and that it has been demonstrated to play an important role in both arthropods and other vertebrates. Using field playback experiments, we tested the hypothesis that adult common toads (Bufo bufo) are capable of recognizing natural vocalizations of a common predator, the Eurasian otter (Lutra lutra), and show antipredator responses. We found that toads exposed to both natural (two types of otter sounds) and synthetic stimuli [white noise (WN) and otter sound‐based amplitude modulated WN] increased time allocated to locomotion and escape behaviour. These responses were correlated with time elapsed from sunset to the onset of testing and were independent from the type of acoustic signal, toad features and other environmental factors monitored. We conclude that B. bufo has not developed a selective recognition of predator vocalizations, suggesting that low‐frequency or seismic sounds associated with predator movements may provide anurans with better cues about an approaching risk. We propose that the time‐dependent response to acoustic stimuli of common toads represents a case of threat‐sensitivity and demonstrates that it can occur even when the response to the threat is not predator specific.

Efficient Encoding of Vocalizations in the Auditory Midbrain

An important question in sensory neuroscience is what coding strategies and mechanisms are used by the brain to detect and discriminate among behaviorally relevant stimuli. There is evidence that sensory systems migrate from a distributed and redundant encoding strategy at the periphery to a more heterogeneous encoding in cortical structures. It has been hypothesized that heterogeneity is an efficient encoding strategy that minimizes the redundancy of the neural code and maximizes information throughput. Evidence of this mechanism has been documented in cortical structures. In this study, we examined whether heterogeneous encoding of complex sounds contributes to efficient encoding in the auditory midbrain by characterizing neural responses to behaviorally relevant vocalizations in the mouse inferior colliculus (IC). We independently manipulated the frequency, amplitude, duration, and harmonic structure of the vocalizations to create a suite of modified vocalizations. Based on measures of both spike rate and timing, we characterized the heterogeneity of neural responses to the natural vocalizations and their perturbed variants. Using information theoretic measures, we found that heterogeneous response properties of IC neurons contribute to efficient encoding of behaviorally relevant vocalizations.

Hemispheric differences in processing of vocalizations depend on early experience

An intriguing phenomenon in the neurobiology of language is lateralization: the dominant role of one hemisphere in a particular function. Lateralization is not exclusive to language because lateral differences are observed in other sensory modalities, behaviors, and animal species. Despite much scientific attention, the function of lateralization, its possible dependence on experience, and the functional implications of such dependence have yet to be clearly determined. We have explored the role of early experience in the development of lateralized sensory processing in the brain, using the songbird model of vocal learning. By controlling exposure to natural vocalizations (through isolation, song tutoring, and muting), we manipulated the postnatal auditory environment of developing zebra finches, and then assessed effects on hemispheric specialization for communication sounds in adulthood. Using bilateral multielectrode recordings from a forebrain auditory area known to selectively process species-specific vocalizations, we found that auditory responses to species-typical songs and long calls, in both male and female birds, were stronger in the right hemisphere than in the left, and that right-side responses adapted more rapidly to stimulus repetition. We describe specific instances, particularly in males, where these lateral differences show an influence of auditory experience with song and/or the bird's own voice during development.

Inhibitory Plasticity in a Lateral Band Improves Cortical Detection of Natural Vocalizations

The interplay between excitation and inhibition in the auditory cortex is crucial for the processing of acoustic stimuli. However, the precise role that inhibition plays in the distributed cortical encoding of natural vocalizations has not been well studied. We recorded single units (SUs) and local field potentials (LFPs) in the awake mouse auditory cortex while presenting pup isolation calls to animals that either do (mothers) or do not (virgins) recognize the sounds as behaviorally relevant. In both groups, we observed substantial call-evoked inhibition. However, in mothers this was earlier, longer, stronger, and more stereotyped compared to virgins. This difference was most apparent for recording sites tuned to tone frequencies lower than the pup calls' high-ultrasonic frequency range. We hypothesize that this auditory cortical inhibitory plasticity improves pup call detection in a relatively specific manner by increasing the contrast between call-evoked responses arising from high-ultrasonic and lateral frequency neural populations.

Effects of valsalva manoeuvre on maternal and fetal wellbeing

The aim of this article is to relate basic findings from research papers to identify the effects that valsalva manoeuvre (‘purple pushing’) has upon maternal and fetal wellbeing. Analysis of 16 papers revealed four main consequences from purple pushing. These include: an increase in fetal distress; maternal distress; and perineal trauma, when compared with spontaneous pushing. Valsalva manoeuvre also makes little difference to length of second stage. Key conclusions from this literature review are that women should be encouraged to push instinctively, which often embraces natural vocalization. Restrictions of time should not be imposed when mother and fetus are well. Awaiting instinctive behaviour reduces the incidence of urinary system, pelvic floor and perineal trauma. These findings should facilitate midwives to critically understand research that underpins the Royal College of Midwives (2007) second stage of labour guidelines.

Sex differences and androgen influences on midbrain auditory thresholds in the green treefrog, Hyla cinerea

Reproductive hormones can modulate communication-evoked behavior by acting on neural systems associated with motivation; however, recent evidence suggests that modulation occurs at the sensory processing level as well. The anuran auditory midbrain processes communication stimuli, and is sensitive to steroid hormones. Using multiunit electrophysiology, we tested whether sex and circulating testosterone influence auditory sensitivity to pure tones and to the natural vocalization in the green treefrog, Hyla cinerea. Sex did not influence audiogram best frequencies although sexes did differ in the sensitivities at those frequencies with males more sensitive in the lower frequency range. Females were more sensitive than males in response to the natural vocalization, despite showing no difference in response to pure tones at frequencies found within the advertisement call. Thresholds to frequencies outside the range of the male advertisement call were higher in females. Additionally, circulating testosterone increased neural thresholds in females in a frequency-specific manner. These results demonstrate that sex differences are limited to frequency ranges that relate to the processing of natural vocalizations, and depend on the type of stimulus. The frequency-dependent and stimulus-dependent nature of sex and testosterone influences suggests that reproductive hormones influence the filtering properties of the auditory system.

Source‐filter interactions in birds—Theory and experimental evidence.

The diverse acoustic behavior of birds presents a rich source of natural vocalizations, some of which most likely reflect source‐filter interaction. However, very little experimental evidence exists for the specific role of such interactions in shaping acoustic behavior or the functional relevance of the resulting acoustic features. As an example of how theoretical approaches can help explain acoustic observations, we discuss coexisting limit cycles in relaxation oscillators subjected to delayed feedback. The dynamical solutions of a nonlinear relaxation oscillator subjected to a delayed feedback are analyzed, and the equations under study are designed to model some aspects of the source‐tract interaction in birdsong production. By deriving a phase equation for the system and analyzing its solutions, we are able to unveil analytical relationships between the parameters that lead to a variety of solutions. In particular, we study the coexistence of periodic solutions for similar pitch and first formant frequencies. These dynamical situations allow us to interpret the frequency jumps present in some birdsong syllables as an effect of the interaction between the source and the tract.

Manatee (Trichechus manatus) vocalization usage in relation to environmental noise levels

Noise can interfere with acoustic communication by masking signals that contain biologically important information. Communication theory recognizes several ways a sender can modify its acoustic signal to compensate for noise, including increasing the source level of a signal, its repetition, its duration, shifting frequency outside that of the noise band, or shifting the timing of signal emission outside of noise periods. The extent to which animals would be expected to use these compensation mechanisms depends on the benefit of successful communication, risk of failure, and the cost of compensation. Here we study whether a coastal marine mammal, the manatee, can modify vocalizations as a function of behavioral context and ambient noise level. To investigate whether and how manatees modify their vocalizations, natural vocalization usage and structure were examined in terms of vocalization rate, duration, frequency, and source level. Vocalizations were classified into two call types, chirps and squeaks, which were analyzed independently. In conditions of elevated noise levels, call rates decreased during feeding and social behaviors, and the duration of each call type was differently influenced by the presence of calves. These results suggest that ambient noise levels do have a detectable effect on manatee communication and that manatees modify their vocalizations as a function of noise in specific behavioral contexts.

A comparison of a child's fundamental frequencies in structured elicited vocalizations versus unstructured natural vocalizations: A case study

Building on the concept that task type may influence fundamental frequency (F(0)) values, the purpose of this case study was to investigate the difference in a child's F(0) during structured, elicited tasks and long-term, unstructured activities. It also explores the possibility that the distribution in children's F(0) may make the standard statistical measures of mean and standard deviation less than ideal metrics. A healthy male child (5 years, 7 months) was evaluated. The child completed four voice tasks used in a previous study of the influence of task type on F(0) values: (1) sustaining the vowel /a/ in isolation; (2) sustaining the vowel /a/ embedded in a word at the end of a phrase; (3) repeating a sentence; and (4) counting from 1 to 10. The child also wore a National Center for Voice and Speech voice dosimeter, a device that collects voice data over the course of an entire day, during all activities for 34 h over 4 days. Throughout the structured vocal tasks within the clinical environment, the child's F(0), as measured by both the dosimeter and acoustic analysis of microphone data, was similar for all four tasks, with the counting task the most dissimilar. The mean F(0) (approximately 257 Hz) matched very closely to the average task results in the literature given for the child's age group. However, the child's mean fundamental frequency during the unstructured activities was significantly higher (approximately 376 Hz). Finally, the mode and median of the structured vocal tasks were 260 Hz and 259 Hz respectively (both near the mean), while the unstructured mode and median were 290 Hz and 355 Hz respectively. The results of this study suggest that children may produce a notably different voice pattern during clinical observations compared to routine daily activities. In addition, the child's long-term F(0) distribution is not normal. If this distribution is consistent in long-term, unstructured natural vocalization patterns of children, statistical mean would not be a valid measure. Mode and median are suggested as two parameters which convey more accurate information about typical F(0) usage. Finally, future research avenues, including further exploration of how children may adapt their F(0) to various environments, conversation partners, and activity, are suggested.

Can free-ranging rhesus monkeys (Macaca mulatta) extract artificially created rules comprised of natural vocalizations?

Though nonhuman animals lack anything like a set of grammatical structures in their natural vocalizations, studies now suggest that at least some animals can extract patterns from a structured input that appear abstract and rule-like. The authors continue this line of research by adding three new methodological contributions, specifically, tests of (1) a free-ranging animal population (as opposed to captive laboratory subjects), (2) a new taxonomic group (i.e., Old World monkeys: rhesus macaques, Macaca mulatta), and (3), the presentation of artificially sequenced strings of species-specific vocalizations (as opposed to artificial symbols or speech stimuli). Specifically, the authors created artificial strings of rhesus vocalizations in the pattern notated as AAB (i.e., two identical calls [AA] followed by a different one [B]) or ABB. Following habituation to AAB strings, rhesus monkeys showed significantly more orienting responses to novel ABB strings than to novel AAB strings. Further, following habituation to an ABB pattern, rhesus responded more in test trials to AAB than ABB. These results, combined with other parallel studies, suggest that animals can extract an identity relationship from an artificial sequence of sounds, and can do so even though the tokens are species-specific vocalizations that are never produced in this sequence.

Sparse codes of harmonic natural sounds and their modulatory interactions

Sparse coding and its related theories have been successful to explain various response properties of early stages of sensory information processing such as primary visual cortex and peripheral auditory system, which suggests that the emergence of such properties results from adaptation of the nerve system to natural stimuli. The present study continues this line of research in a higher stage of auditory processing, focusing on harmonic structures that are often found in behaviourally important natural sound like animal vocalization. It has been physiologically shown that monkey primary auditory cortices (A1) have neurons with response properties capturing such harmonic structures: their response and modulation peaks are often found at frequencies that are harmonically related to each other. We hypothesize that such relations emerge from sparse coding of harmonic natural sounds. Our simulation shows that similar harmonic relations emerge from frequency-domain sparse codes of harmonic sounds, namely, piano performance and human speech. Moreover, the modulatory behaviours can be explained by competitive interactions of model neurons that capture partially common harmonic structures.

Central pattern generators for social vocalization: Androgen-dependent neurophysiological mechanisms

Historically, most studies of vertebrate central pattern generators (CPGs) have focused on mechanisms for locomotion and respiration. Here, we highlight new results for ectothermic vertebrates, namely teleost fish and amphibians, showing how androgenic steroids can influence the temporal patterning of CPGs for social vocalization. Investigations of vocalizing teleosts show how androgens can rapidly (within minutes) modulate the neurophysiological output of the vocal CPG (fictive vocalizations that mimic the temporal properties of natural vocalizations) inclusive of their divergent actions between species, as well as intraspecific differences between male reproductive morphs. Studies of anuran amphibians (frogs) demonstrate that long-term steroid treatments (wks) can masculinize the fictive vocalizations of females, inclusive of its sensitivity to rapid modulation by serotonin. Given the conserved organization of vocal control systems across vertebrate groups, the vocal CPGs of fish and amphibians provide tractable models for identifying androgen-dependent events that are fundamental to the mechanisms of vocal motor patterning. These basic mechanisms can also inform our understanding of the more complex CPGs for vocalization, and social behaviors in general, that have evolved among birds and mammals.

Can birds discriminate between simple sounds and natural vocalization with different degrees of reverberation

Birds in natural habitats using long-range acoustic signals experience substantial acoustic alterations of their signals when transmitted from a sender to a receiver. The main degradation comes from reflections of the emitted sounds from surfaces in and around the transmission pathway. These reverberations cause tails of echoes and affect frequency and amplitude modulation within the sounds’ original time frame. Humans discriminate among reverberant and nonreverberant speech segments and use the nature of reverberation in determining the location of the sound source. Using operant conditioning and psychophysical methods, we investigated the ability of several species of small birds to discriminate between nondegraded sounds and sounds artificially reverberated to varying degrees, while holding other sound aspects constant. Birds were able to easily discriminate between nonreverberant sounds and sounds reverberated to various extents. By comparing the birds’ performance on stimuli varying along different dimensions of reverberation, we can make predictions as to the birds ability to use reverberations as acoustic cues in distance estimation and locating sound sources. [Work supported by NICD DC000198 (to R.J.D.) and DC004664.]

The discrimination of temporal fine structure in call-like harmonic sounds by birds.

Thresholds for discriminating changes in the temporal fine structure of call-like, harmonic sounds were measured in zebra finches (Taeniopygia guttata) and budgerigars (Melopsittacus undulatus). Birds could detect changes in periods as short as 1.225 ms at near 100% accuracy even when spectral and envelope cues were identical, as in time-reversed stimuli. Humans performed poorly on such stimuli, paralleling results from previous studies. Bird thresholds were in the range of those reported in neurophysiological studies of the songbird high vocal center (HVC) to temporally modified conspecific songs. Taken together, these results show that birds can hear differences in temporal fine structure in their natural vocalizations that go beyond human capabilities, but whether these abilities have communicative relevance remains to be seen.

Echolocation calls and communication calls are controlled differentially in the brainstem of the bat Phyllostomus discolor

BackgroundEcholocating bats emit vocalizations that can be classified either as echolocation calls or communication calls. Neural control of both types of calls must govern the same pool of motoneurons responsible for vocalizations. Electrical microstimulation in the periaqueductal gray matter (PAG) elicits both communication and echolocation calls, whereas stimulation of the paralemniscal area (PLA) induces only echolocation calls. In both the PAG and the PLA, the current thresholds for triggering natural vocalizations do not habituate to stimuli and remain low even for long stimulation periods, indicating that these structures have relative direct access to the final common pathway for vocalization. This study intended to clarify whether echolocation calls and communication calls are controlled differentially below the level of the PAG via separate vocal pathways before converging on the motoneurons used in vocalization.ResultsBoth structures were probed simultaneously in a single experimental approach. Two stimulation electrodes were chronically implanted within the PAG in order to elicit either echolocation or communication calls. Blockade of the ipsilateral PLA site with iontophoretically application of the glutamate antagonist kynurenic acid did not impede either echolocation or communication calls elicited from the PAG. However, blockade of the contralateral PLA suppresses PAG-elicited echolocation calls but not communication calls. In both cases the blockade was reversible.ConclusionThe neural control of echolocation and communication calls seems to be differentially organized below the level of the PAG. The PLA is an essential functional unit for echolocation call control before the descending pathways share again the final common pathway for vocalization.

Vocal Pathways Modulate Efferent Neurons to the Inner Ear and Lateral Line

All sonic vertebrates face the problem of sound production interfering with their ability to detect and process external acoustic signals, including conspecific vocalizations. Direct efferent inputs to the inner ear of all vertebrates, and the lateral line system of some aquatic vertebrates, represent a potential mechanism to adjust peripheral sensitivity during sound production. We recorded from single efferent neurons that innervate the inner ear and lateral line in a sound-producing teleost fish while evoking fictive vocalizations predictive of the temporal features of natural vocalizations. The majority of efferent neurons showed an increase in activity that occurred in-phase with modulations in the fine temporal structure of the fictive vocalizations. Many of these neurons also showed a decrease in activity at fictive vocal offset. Efferents to the sacculus, the main auditory end organ, showed features especially well adapted for maintaining sensitivity to external acoustic signals during sound production. These included robust phase locking of efferent activity to each cycle of a fictive vocalization and a long-duration rebound suppression after each fictive vocalization that could provide a rapid, long-lasting period of sensitization to external acoustic stimuli such as the call of a conspecific. These results suggest that efferent activation by the vocal motor system can directly modulate auditory sensitivity to self-generated sounds and maintain sensitivity to ongoing external sounds. Given the conserved organization of the auditory efferent system across vertebrates, such mechanisms may be operative among all sonic vertebrates.