Vocal Responses Research Articles

Does level of cognitive load affect susceptibility?

We compared how different levels of cognitive load affect frontal P3 (fP3) Event-Related Potential (ERP) to novel sounds. Previous studies demonstrated the predictive value of the probe-elicited frontal P3 (fP3) ERP for subsequent detection failures. They also demonstrated how fP3 is reduced when performing visual and/or manual and/or cognitively demanding tasks. These results are consistent with fP3 indexing orienting to novels or, more neutrally: susceptibility. Here, we tested how fP3 is affected by a threefold variation of cognitive load induced by the verb (generation) task. Participants heard a noun and either listened to it, repeated it, or generated a semantically related verb. These conditions were manipulated between groups. One group (N = 16) experienced the listen and repeat condition; the other group (N = 16) experienced the listen and generate condition. When fP3 was probed 0 or 200 ms after noun offset, it was reduced (relative to no noun) only while repeating or generating, not while listening. An additional probe-elicited ERP was identified as novelty-related negativity, and its contaminating influence on fP3 estimation accounted for by a novel vector-filter procedure. We conclude that cognitive load does not affect fP3-indexed susceptibility. Instead, fP3-indexed susceptibility is affected by presentation of the stimulus, with the most pronounced effect in conditions where a vocal response is needed (i.e., repeat or generate, but not listen), independent of the complexity of the response.

Behavioral responses of free-ranging Japanese macaques (Macaca fuscata) to sudden loud noises.

We opportunistically observed 31 cases of responses to sudden loud noises mainly caused by falling rocks and trees in a free-ranging, provisioned group of Japanese macaques, Macaca fuscata, at Katsuyama, Japan, and analyzed 27 cases for which we successfully recorded their responses. In 88% of the 24 cases in which the highest- or second-highest ranking adult male probably heard the noise, one or both of them vocalized aggressively in response. Other males tended to vocalize when they were far away from the two highest-ranking males (in 5 of 7 cases in which they vocalized). Adult females vocalized in only 8% of cases, even when they fled from the noise source. These findings suggest that, unlike tree-shaking and female-directed aggression- both performed often in the mating season and accompanied by vocalizations in both high- and low-ranking males of Japanese macaques- vocalizing in response to sudden loud noises is usually limited to one or two high-ranking males in the vicinity. This vocal response could be a way for the males to advertise their social status; it may also serve to calm group members scared by the noise, preventing them from fleeing in panic and dispersing widely. Our observations also suggest that males may monitor which other males remain nearby, and that whereas females may scream in response to socially induced fear, they are least likely to do so in response to fear arising from non-social contexts.

Sound and vibration control crocodile hatching

Abstract The birth of a baby or the hatching of an egg are moments when the risk of predation is particularly high. In oviparous species where clutches contain many eggs, one strategy for limiting predation is based on mechanisms that synchronise hatching, which reduces the individual risk of being targeted and may allow hatchlings to emerge under parental protection. These mechanisms involve communication signals between eggs and between eggs and parents. While previous studies in various species have shown the importance of sound and vibration signals in these exchanges, how embryos integrate this information remains poorly understood. Here we show that crocodile embryos respond differently to calls emitted by siblings (hatching calls) and to vibrations mimicking parental intervention (rubbing and scratching the shell) or the presence of a predator, suggesting that these two stimuli carry different information. Through playback experiments, we confirm that hatching calls elicit vocal responses and synchronous hatching in mature embryos, while embryos hatch earlier when they perceive vibrations. Our study underlines that the control of hatching by external factors can rely on differential apprehension of multiple sensory inputs by embryos.

Anuran communities increase aggregations of conspecific calls in response to aircraft noise

Abstract Noise pollution has been shown to affect wild animals in various ways, but little is known about its consequences at the community level. Investigating animals’ overall vocal responses to noise across multiple sympatric species can reveal the complex nature of noise impacts but is challenging. In this study, we employed social network analysis (SNA) to evaluate how anuran communities and populations vary their calling behaviors in response to aircraft noise. SNA of anuran communities revealed that conspecific individuals increase the aggregation of their spectral (i.e., minimum frequency, maximum frequency, and dominant frequency), temporal (call duration, call rate, and call effort), and overall spectral–temporal features as an airplane passes through. SNA of populations also revealed that anurans could increase the interindividual similarity of multiple call characteristics in response to airplane noise. Furthermore, our network analysis of multiple species and multiple call traits revealed an effect of noise in species whose calling behavior did not change in previous separate analyses of each species and single traits. This study suggests that noise pollution may change the pattern of combined acoustic properties at the community level. Our findings highlight the importance of integrated methods and theories for understanding the ecological consequences of noise pollution in future studies.

Tarikh Falsafah al-Lughah al-Insaniyah

There are many differences in the discussion of the origin of language. The results of studies on this issue have not been conclusive due to the difficulty researchers face in reaching a consensus. So, what is the history of the origin of language in this world? There are many theories about the origin of language to answer this problem. The aim of this research is to uncover the history of the emergence of language. The approach of this research is qualitative. The researcher used the library method for her research. She collected data through documentation, which involved reading books, articles, and research related to this topic. The data analysis method used in this research is content analysis. The results of this research are that the researcher found various theories about the origin of language, including the divine theory, the convention theory, the Bow-wow theory (theory of natural sound imitation), the Pooh-pooh theory (theory of emotional exclamations), the Yo-he-ho theory (theory of vocal responses to muscular movements), and the like. None of these theories are entirely right or wrong, but language encompasses all of them.

Variation in responses to conspecific and heterospecific advertisement vocalizations in sympatric grasshopper mice (Onychomys).

Advertisement vocalizations that function in mate acquisition and resource defense within species may also mediate behavioral interactions among species. While olfactory signals play an important role in mate choice and territoriality in rodents, less is known about the function of acoustic signals in influencing interspecific interactions. In this study, we used playback experiments in the laboratory to assess the function of long-distance vocalizations within and among three sympatric species of grasshopper mice. We found that, within each species, individuals of both sexes varied widely in spontaneous vocal behavior and response to playback. The largest species (Onychomys leucogaster) was most responsive to conspecifics, but smaller O. arenicola and O. torridus exhibited no clear pattern in their vocal behavior and were even responsive to the white noise controls. Our results indicate that grasshopper mice are broadly responsive to a range of sounds that resemble calls and that long-distance vocalizations function primarily as signals that facilitate localization for subsequent close-distance assessment by both sexes in various social contexts. Variation in vocal responses among species may depend on competitive dominance, degree of interaction, acoustic similarity, or behavioral changes resulting from captivity. Replicating playback experiments in the field will help validate whether the observed variation in the laboratory reflects ecologically relevant patterns in nature.

Fast and friendly: The role of vocal cues in adolescents' responses to and perceptions of peer provocation.

Adolescents self-report using different strategies to respond to peer provocation. However, we have a limited understanding of how these responses are behaviorally enacted and perceived by peers. This study examined the extent to which adolescents' self-reported responses to peer provocation (i.e., aggressive, assertive, and withdrawn) predicted how their vocal enactments of standardized responses to peer provocation were perceived by other adolescents. Three vocal cues relevant to the communication of emotional intent-average pitch, average intensity, and speech rate-were explored as moderators of these associations. Adolescent speakers (n = 39; Mage = 12.67; 66.7% girls) completed a self-report measure of how they would choose to respond to scenarios involving peer provocation; they also enacted standardized vocal responses to hypothetical peer provocation scenarios. Recordings of speakers' vocal responses were presented to a separate sample of adolescent listeners (n = 129; Mage = 12.12; 52.7% girls) in an online listening task. Speakers who self-reported greater use of assertive response strategies enacted standardized vocal responses that were rated as significantly friendlier by listeners. Vocal responses enacted with faster speech rates were also rated as significantly friendlier by listeners. Speakers' self-reported use of aggression and withdrawal was not significantly related to listeners' ratings of their standardized vocal responses. These findings suggest that adolescents may be perceived differently by their peers depending on the way in which their response is enacted; specifically, faster speech rate may be perceived as friendlier and thus de-escalate peer conflict. Future studies should consider not only what youth say and/or do when responding to peer provocation but also how they say it.

In Vitro Investigation of Vocal Fold Cellular Response to Variations in Hydrogel Porosity and Elasticity.

Tissue regeneration is intricately influenced by the dynamic interplay between the physical attributes of tissue engineering scaffolds and the resulting biological responses. A tunable microporous hydrogel system was engineered using gelatin methacryloyl (GelMA) and polyethylene glycol diacrylate (PEGDA), with polyethylene glycol (PEG) serving as a porogen. Through systematic variation of PEGDA molecular weights, hydrogels with varying mechanical and architectural properties were obtained. The objective of the present study was to elucidate the impact of substrate mechanics and architecture on the immunological and reparative activities of vocal fold tissues. Mechanical characterization of the hydrogels was performed using tensile strength measurements and rheometry. Their morphological properties were investigated using scanning electron microscopy (SEM) and confocal microscopy. A series of biological assays were conducted. Cellular morphology, differentiation, and collagen synthesis of human vocal fold fibroblasts (hVFFs) were evaluated using immunostaining. Fibroblast proliferation was studied using the WST-1 assay, and cell migration was investigated via the Boyden chamber assay. Macrophage polarization and secretions were also examined using immunostaining and ELISA. The results revealed that increasing the molecular weight of PEGDA from 700 Da to 10,000 Da resulted in decreased hydrogel stiffness, from 62.6 to 8.8 kPa, and increased pore dimensions from approximately 64.9 to 137.4 μm. Biological evaluations revealed that hydrogels with a higher stiffness promoted fibroblast proliferation and spreading, albeit with an increased propensity for fibrosis, as indicated by a surge in myofibroblast differentiation and collagen synthesis. In contrast, hydrogels with greater molecular weights had a softer matrix with expanded pores, enhancing cellular migration and promoting an M2 macrophage phenotype conducive to tissue healing. The findings show that the hydrogels formulated with a PEGDA molecular weight of 6000 Da are best among the hydrogels considered for vocal fold repair. The microporous hydrogels could be tuned to serve in other tissue engineering applications.

The late positive event-related potential component is time locked to the decision in recognition memory tasks

Two event-related potential (ERP) components are commonly observed in recognition memory tasks: the Frontal Negativity (FN400) and the Late Positive Component (LPC). These components are widely interpreted as neural correlates of familiarity and recollection, respectively. However, the interpretation of LPC effects is complicated by inconsistent results regarding the timing of ERP amplitude differences. There are also mixed findings regarding how LPC amplitudes covary with decision confidence. Critically, LPC effects have almost always been measured using fixed time windows relative to memory probe stimulus onset, yet it has not been determined whether LPC effects are time locked to the stimulus or the recognition memory decision. To investigate this, we analysed a large (n = 132) existing dataset recorded during recognition memory tasks with old/new decisions followed by post-decisional confidence ratings. We used ERP deconvolution to disentangle contributions to LPC effects (defined as differences between hits and correct rejections) that were time locked to either the stimulus or the vocal old/new response. We identified a left-lateralised parietal LPC effect that was time locked to the vocal response rather than probe stimulus onset. We also isolated a response-locked, midline parietal ERP correlate of confidence that influenced measures of LPC amplitudes at left parietal electrodes. Our findings demonstrate that, contrary to widespread assumptions, the LPC effect is time locked to the recognition memory decision and is best measured using response-locked ERPs. By extension, differences in response time distributions across conditions of interest may lead to substantial measurement biases when analysing stimulus-locked ERPs. Our findings highlight important confounding factors that further complicate the interpretation of existing stimulus-locked LPC effects as neural correlates of recollection. We recommend that future studies adopt our analytic approach to better isolate LPC effects and their sensitivity to manipulations in recognition memory tasks.

Caregiver reactions to babbling organize turn-taking interactions: Facilitative effects of vocal versus non-vocal responses.

Turn-taking interactions are foundational to the development of social, communicative, and cognitive skills. In infants, vocal turn-taking experience is predictive of infants' socioemotional and language development. However, different forms of turn-taking interactions may have different effects on infant vocalizing. It is presently unknown how caregiver vocal, non-vocal and multimodal responses to infant vocalizations compare in extending caregiver-infant vocal turn-taking bouts. In bouts that begin with an infant vocalization, responses that maintain versus change the communicative modality may differentially affect the likelihood of further infant vocalizing. No studies have examined how caregiver response modalities that either matched or differed from the infant acoustic (vocal) modality might affect the temporal structure of vocal turn-taking beyond the initial serve-and-return exchanges. We video-recorded free-play sessions of 51 caregivers with their 9-month-old infants. Caregivers responded to babbling most often with vocalizations. In turn, caregiver vocal responses were significantly more likely to elicit subsequent infant babbling. Bouts following an initial caregiver vocal response contained significantly more turns than those following a non-vocal or multimodal response. Thus prelinguistic turn-taking is sensitive to the modality of caregivers' responses. Future research should investigate if such sensitivity is grounded in attentional constraints, which may influence the structure of turn-taking interactions.

Imitation of Computer-Generated Sounds by Wild Atlantic Spotted Dolphins (Stenella frontalis)

Since 1985 a community of wild Atlantic spotted dolphin (Stenella frontalis) have been observed underwater in the Bahamas. A human-worn, acoustic underwater two-way communication interface was developed and deployed from 2013-2016. Dolphins were exposed to an acoustic referentially based wearable underwater computer/interface. A model/rival system was used with dolphins and human participants during in-water sessions. Artificial and natural objects were labeled with computer generated sounds. Female juvenile spotted dolphins dominated the activity. Group size averaged seven dolphins for an average duration of 37 minute over 58 sessions. Of 243 video audio imitations and 56 Cetacean Hearing Augmentation Telemetry (CHAT) audio imitations, six potential response types were documented and measured. Stand-alone vocal contour mimics and Frequency Modulated Contours were the most common imitations. Within 5 sec of a computer-generated sound playing, of the 191 non-stand-alone vocal responses that were produced, 114 of them (59.7%) were judged as partial accurate matches, 3 of them (1.57%) were judged as non-matching partial imitations of a computer-generated sound, 67 of them (35.08%) were signature whistles, and seven of them (3.67%) were either non-signature whistle vocalizations or a mimic of the start or end tones. Thus, the majority of vocalizations produced by the dolphins within five seconds of a computer-generated sound were partial accurate imitations for the computer-generated sound played. Dolphins demonstrated both immediate and delayed vocal imitation and flexible attempts at imitation but did not show signs of a functional understanding of object labels. Atlantic spotted dolphins showed vocal flexibility in reaction to humans broadcasting computer generated sounds.

A spatial version of the Stroop task for examining proactive and reactive control independently from non-conflict processes.

Conflict-induced control refers to humans' ability to regulate attention in the processing of target information (e.g., the color of a word in the color-word Stroop task) based on experience with conflict created by distracting information (e.g., an incongruent color word), and to do so either in a proactive (preparatory) or a reactive (stimulus-driven) fashion. Interest in conflict-induced control has grown recently, as has the awareness that effects attributed to those processes might be affected by conflict-unrelated processes (e.g., the learning of stimulus-response associations). This awareness has resulted in the recommendation to move away from traditional interference paradigms with small stimulus/response sets and towards paradigms with larger sets (at least four targets, distractors, and responses), paradigms that allow better control of non-conflict processes. Using larger sets, however, is not always feasible. Doing so in the Stroop task, for example, would require either multiple arbitrary responses that are difficult for participants to learn (e.g., manual responses to colors) or non-arbitrary responses that can be difficult for researchers to collect (e.g., vocal responses in online experiments). Here, we present a spatial version of the Stroop task that solves many of those problems. In this task, participants respond to one of six directions indicated by an arrow, each requiring a specific, non-arbitrary manual response, while ignoring the location where the arrow is displayed. We illustrate the usefulness of this task by showing the results of two experiments in which evidence for proactive and reactive control was obtained while controlling for the impact of non-conflict processes.

Sound symbolism in manual and vocal responses: phoneme-response interactions associated with grasping as well as vertical and size dimensions of keypresses

It has been shown that reading the vowel [i] and consonant [t] facilitates precision grip responses, while [ɑ] and [k] are associated with faster power grip responses. A similar effect has been observed when participants perform responses with small or large response keys. The present study investigated whether the vowels and consonants could produce different effects with the grip responses and keypresses when the speech units are read aloud (Experiment 1) or silently (Experiment 2). As a second objective, the study investigated whether the recently observed effect, in which the upper position of a visual stimulus is associated with faster vocalizations of the high vowel and the lower position is associated with the low vowel, can be observed in manual responses linking, for example, the [i] with responses of the upper key and [ɑ] with lower responses. Firstly, the study showed that when the consonants are overtly articulated, the interaction effect can be observed only with the grip responses, while the vowel production was shown to systematically influence small/large keypresses, as well as precision/power grip responses. Secondly, the vowel [i] and consonant [t] were associated with the upper responses, while [ɑ] and [k] were associated with the lower responses, particularly in the overt articulation task. The paper delves into the potential sound-symbolic implications of these phonetic elements, suggesting that their acoustic and articulatory characteristics might implicitly align them with specific response magnitudes, vertical positions, and grip types.

Developmental cascades of vocal turn-taking connect prelinguistic vocalizing with early language

Conversational turn-taking is ubiquitously found in caregiver-infant interactions, and robustly predictive of infant communicative development. Over the first year, infants take quick adult-like vocal turns with caregivers. Many studies have documented the consistency of caregiver responsiveness and its influence on infant rapid language growth. However, few have examined how caregiver responsiveness facilitates extended vocal turn-taking in real-time with infants over the first year. The influence of prelinguistic vocal turn-taking on the emergence of language has also been under-investigated. We analyzed free-play sessions of 30 caregivers and their infants at both 5 and 10 months, and obtained infant language outcomes at 18 months. We examined the developmental consistency (group-level continuity and dyad-order stability) and change of infant volubility, caregiver responses to babbling in vocal, non-vocal and multimodal modalities, and the influence of modality on caregiver-infant vocal turn-taking. Caregiver contingent responsiveness to infant babbling at 5 months predicted vocal turn-taking at 10 months. Developmental increases in prelinguistic vocalizing and vocal turn-taking from 5 to 10 months predicted infant language outcomes at 18 months. At both 5 and 10 months, caregiver vocal responses were more effective in extending turn-taking than non-vocal or multimodal responses. In summary, prelinguistic vocal turn-taking, facilitated by caregiver vocal responsiveness, is positively related to the emergence of early language.

Temporal Characteristics of Infant Vocalization during Interaction with Adults

Objectives: This study aimed to examine the temporal characteristics of infant vocalizations during interactions with adults in natural home environments.Methods: One day LENA (Language ENvironment Analysis) recordings were collected from 20 infants aged 6 and 12 months. The collected data were analyzed by selecting 20 5-mintue intervals in the order of highest CTCs (conversational turn counts). In the analysis unit of turn-taking, interactions in which the infant responded within 0.05 seconds to 3 seconds after the adult spoke directly to the infant were regarded as one analysis unit. The temporal characteristics of infant vocalization during interactions with adults were examined through infants’ Vocalization response ratio. The temporal characteristics of infant vocalization in interactions with adults were examined by the after adults’ infant-directed speech (IDS), latency of vocalization response and overlapping vocalization ratio.Results: Infants’ Vocalization response ratio following IDS in adults did not differ significantly between the two age groups. Infants’ Vocalization response latencies increased significantly with age from 6 to 12 months. Overlapping vocalization ratio showed a significant decrease with increasing age.Conclusion: This study supports that as infants grow, they acquire temporal turn-taking skills. It also suggests that the temporal characteristics of infant vocalizations during interactions with adults may be a useful to predict infants’ language development.

The Mouse Inferior Colliculus Responds Preferentially to Non-Ultrasonic Vocalizations.

The inferior colliculus (IC), the midbrain auditory integration center, analyzes information about social vocalizations and provides substrates for higher level processing of vocal signals. We used multichannel recordings to characterize and localize responses to social vocalizations and synthetic stimuli within the IC of female and male mice, both urethane anesthetized and unanesthetized. We compared responses to ultrasonic vocalizations (USVs) with other vocalizations in the mouse repertoire and related vocal responses to frequency tuning, IC subdivisions, and sex. Responses to lower frequency, broadband social vocalizations were widespread in IC, well represented throughout the tonotopic axis, across subdivisions, and in both sexes. Responses to USVs were much more limited. Although we observed some differences in tonal and vocal responses by sex and subdivision, representations of vocal responses by sex and subdivision were largely the same. For most units, responses to vocal signals occurred only when frequency response areas overlapped with spectra of the vocal signals. Since tuning to frequencies contained within the highest frequency USVs is limited (<15% of IC units), responses to these vocalizations are correspondingly limited (<5% of sound-responsive units). These results highlight a paradox of USV processing in some rodents: although USVs are the most abundant social vocalization, their representation and the representation of corresponding frequencies are less than lower frequency social vocalizations. We interpret this paradox in light of observations suggesting that USVs with lower frequency elements (<50 kHz) are associated with increased emotional intensity and engage a larger population of neurons in the mouse auditory system.

Handedness and effector strength modulate a compatibility effect between stimulus size and response position with manual and vocal responses.

Humans respond more quickly with the left hand to a small stimulus, and with the right hand to a large stimulus, as compared to the reverse mapping (spatial-size association of response codes [SSARC] effect). We investigated the hypothesis that strength differences between the hands contribute to the origin of this effect. Therefore, 80 left-handers and 80 right-handers participated in two experiments. In Experiment 1, participants performed a manual choice-response task in which we manipulated the mapping between physical stimulus size and responding hand. In addition, we measured the strengths of participants' left and right effectors (i.e., finger, hand, and arm). In Experiment 2, we measured the SSARC effect in vocal responses of the same sample. There were four main results. First, participants' dominant effectors were stronger than their nondominant effectors. Second, the SSARC effect occurred in manual and vocal responses with similar size. Third, in both modalities, the SSARC effect was larger in right-handers than in left-handers. Finally, strength differences between effectors (fingers and hands) correlated with the size of the SSARC effect. In sum, results support the hypothesis that functional differences between the hands contribute to the origin of the SSARC effect. In addition, the results suggest that size-space associations have generalized across motor systems, and formed a modality-independent association. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Voluntary task switching is affected by modality compatibility and preparation

Cognitive task control can be examined in task-switching studies. Performance costs in task switches are usually smaller with compatible stimulus-response modality mappings (visual-manual and auditory-vocal) than with incompatible mappings (visual-vocal and auditory-manual). Modality compatibility describes the modality match of sensory input and of the anticipated response effect (e.g., vocal responses produce auditory effects, so that auditory stimuli are modality-compatible with vocal responses). Fintor et al. (Psychological Research, 84(2), 380–388, 2020) found that modality compatibility also biased task choice rates in voluntary task switching (VTS). In that study, in each trial participants were presented with a visual or auditory spatial stimulus and were free to choose the response modality (manual vs. vocal). In this free-choice task, participants showed a bias to create more modality-compatible than -incompatible mappings. In the present study, we assessed the generality of Fintor et al.’s (2020) findings, using verbal rather than spatial stimuli, and more complex tasks, featuring an increased number of stimulus-response alternatives. Experiment 1 replicated the task-choice bias to preferentially create modality-compatible mappings. We also found a bias to repeat the response modality just performed, and a bias to repeat entire stimulus-response modality mappings. In Experiment 2, we manipulated the response-stimulus interval (RSI) to examine whether more time for proactive cognitive control would help resolve modality-specific crosstalk in this free-choice paradigm. Long RSIs led to a decreased response-modality repetition bias and mapping repetition bias, but the modality-compatibility bias was unaffected. Together, the findings suggest that modality-specific priming of response modality influences task choice.

Neighbour–stranger discrimination in an African wood dove inhabiting equatorial rainforest

We investigated within- and between-individual song variation and song-based neighbour-stranger discrimination in a non-learning bird species, the blue-headed wood-dove (Turtur brehmeri), which inhabits lowland rainforests of West and Central Africa. We found that songs of this species are individually specific and have a high potential for use in individual recognition based on the time–frequency pattern of note distribution within song phrases. To test whether these differences affect behaviour, we conducted playback experiments with 19 territorial males. Each male was tested twice, once with the songs of a familiar neighbour and once with the songs of an unfamiliar stranger. We observed that males responded more aggressively to playback of a stranger’s songs: they quickly approached close to the speaker and spent more time near it. However, no significant differences between treatments were observed in the vocal responses. In addition, we explored whether responses differed based on the song frequency of the focal male and/or that of the simulated intruder (i.e., playback), as this song parameter is inversely related to body size and could potentially affect males’ decisions to respond to other birds. Song frequency parameters (of either the focal male or the simulated intruder) had no effect on the approaching response during playback. However, we found that the pattern of response after playback was significantly affected by the song frequency of the focal male: males with lower-frequency songs stayed closer to the simulated intruder for a longer period of time without singing, while males with higher-frequency songs returned more quickly to their initial song posts and resumed singing. Together, these results depict a consistently strong response to strangers during and after playback that is dependent on a male’s self-assessment rather than assessment of a rival’s strength based on his song frequency. This work provides the first experimental evidence that doves (Columbidae) can use songs for neighbour-stranger discrimination and respond according to a “dear enemy” scheme that keeps the cost of territory defence at a reasonable level.

Mantled howler monkey males assess their rivals through formant spacing of long-distance calls.

Formant frequency spacing of long-distance vocalizations is allometrically related to body size and could represent an honest signal of fighting potential. There is, however, only limited evidence that primates use formant spacing to assess the competitive potential of rivals during interactions with extragroup males, a risky context. We hypothesized that if formant spacing of long-distance calls is inversely related to the fighting potential of male mantled howler monkeys (Alouatta palliata), then males should: (1) be more likely and (2) faster to display vocal responses to calling rivals; (3) be more likely and (4) faster to approach calling rivals; and have higher fecal (5) glucocorticoid and (6) testosterone metabolite concentrations in response to rivals calling at intermediate and high formant spacing than to those with low formant spacing. We studied the behavioral responses of 11 adult males to playback experiments of long-distance calls from unknown individuals with low (i.e., emulating large individuals), intermediate, and high (i.e., small individuals) formant spacing (n = 36 experiments). We assayed fecal glucocorticoid and testosterone metabolite concentrations (n = 174). Playbacks always elicited vocal responses, but males responded quicker to intermediate than to low formant spacing playbacks. Low formant spacing calls were less likely to elicit approaches whereas high formant spacing calls resulted in quicker approaches. Males showed stronger hormonal responses to low than to both intermediate and high formant spacing calls. It is possible that males do not escalate conflicts with rivals with low formant spacing calls if these are perceived as large, and against whom winning probabilities should decrease and confrontation costs increase; but are willing to escalate conflicts with rivals of high formant spacing. Formant spacing may therefore be an important signal for rival assessment in this species.