Transcontinental latitudinal variation in song performance and complexity in house wrens (Troglodytes aedon).

There is growing interest in latitudinal effects on animal behaviour and life history. One recent focus is on birdsong, which is hypothesized to be more elaborated or complex in the north temperate zone compared with the tropics. Current evidence is mixed and based on cross-species comparisons, or single species with restricted distributions. We circumvent these limitations using a transcontinental sample of 358 songs from house wrens (Troglodytes aedon) at 281 locations spanning more than 100° of latitude (52° N-55° S) across the Americas. We found a significant latitudinal gradient in several basic elements of song performance and complexity between north temperate and tropical populations. Furthermore, we document convergence in song patterns between populations at higher latitudes in the Northern and Southern Hemispheres. Effects were strongest for the number of elements in a song, and the rate of element production, both increasing towards the poles, with similar but weaker effects for other song dimensions (e.g. number of unique elements, trills and trill rate). We consider possible causes related to variable habitats and morphology, concluding that the shorter breeding seasons at higher latitudes in both hemispheres may favour greater song elaboration to mediate territory competition and mate choice.

Sexual selection on male vocal fundamental frequency in humans and other anthropoids.

In many primates, including humans, the vocalizations of males and females differ dramatically, with male vocalizations and vocal anatomy often seeming to exaggerate apparent body size. These traits may be favoured by sexual selection because low-frequency male vocalizations intimidate rivals and/or attract females, but this hypothesis has not been systematically tested across primates, nor is it clear why competitors and potential mates should attend to vocalization frequencies. Here we show across anthropoids that sexual dimorphism in fundamental frequency (F0) increased during evolutionary transitions towards polygyny, and decreased during transitions towards monogamy. Surprisingly, humans exhibit greater F0 sexual dimorphism than any other ape. We also show that low-F0 vocalizations predict perceptions of men's dominance and attractiveness, and predict hormone profiles (low cortisol and high testosterone) related to immune function. These results suggest that low male F0 signals condition to competitors and mates, and evolved in male anthropoids in response to the intensity of mating competition.

Cranio-facial remodeling in domestic dogs is associated with changes in larynx position.

The hyo-laryngeal complex is a multi-segmented structure integrating the oral and pharyngeal cavities and thus a variety of critical functions related to airway control, feeding, and vocal communication. Currently, we lack a complete understanding of how the hyoid complex, and the functions it mediates, can also be affected by changes in surrounding cranio-facial dimensions. Here, we explore these relationships in a breed of domestic dog, the Portuguese Water Dog, which is characterized by strong cranio-facial variation. We used radiographic images of the upper body and head of 55 adult males and 51 adult females to obtain detailed measures of cranio-facial variation and hyoid anatomy. Principal components analysis revealed multiple orthogonal dimensions of cranio-facial variation, some of which were associated with significant differences in larynx position: the larynx occupied a more descended position in individuals with shorter, broader faces than in those with longer, narrower faces. We then tested the possibility that caudal displacement of the larynx in brachycephalic individuals might reflect a degree of tongue crowding resulting from facial shortening and reduction of oral and pharyngeal spaces. A cadaver sample was used to obtain detailed measurements of constituent bones of the hyoid skeleton and of the tongue body, and their relationships to cranio-facial size and shape and overall body size supported the tongue-crowding hypothesis. Considering the presence of descended larynges in numerous mammalian taxa, our findings establish an important precedent for the possibility that laryngeal descent can be initiated, and even sustained, in part in response to remodeling of the face and cranium for selective pressures unrelated to vocal production. These integrated changes could also have been involved in hominin evolution, where the different laryngeal positions in modern humans compared with nonhuman primates have been traditionally linked to the evolution of speech but which are likely to be multifactorial.

Learning to differentiate individuals by their voices: Infants' individuation of native- and foreign-species voices.

The ability to discriminate and identify people by their voice is important for social interaction in humans. In early development, learning to discriminate important differences in a number of socially relevant stimuli, such as phonemes and faces, has been shown to follow a common pattern of experience-driven perceptual narrowing, where the discrimination of native stimuli improves, while the discrimination of foreign stimuli worsens. The aim of the present study was to investigate whether similar perceptual narrowing occurs for discriminating individuals by voice. We tested the ability of English-speaking adults and English-learning 6- and 12-month-olds to discriminate either native-species (human) or foreign-species (rhesus monkey [Macaca mulatta]) individuals by their vocalizations. Between 6 and 12 months of age, the ability to discriminate monkey voices decreased significantly and there was a non-significant trend for improved ability to discriminate human voices. The results support the hypothesis of experience-driven perceptual narrowing for voice individuation during the first year after birth.

Two organizing principles of vocal production: Implications for nonhuman and human primates.

Vocal communication in nonhuman primates receives considerable research attention, with many investigators arguing for similarities between this calling and speech in humans. Data from development and neural organization show a central role of affect in monkey and ape sounds, however, suggesting that their calls are homologous to spontaneous human emotional vocalizations while having little relation to spoken language. Based on this evidence, we propose two principles that can be useful in evaluating the many and disparate empirical findings that bear on the nature of vocal production in nonhuman and human primates. One principle distinguishes production-first from reception-first vocal development, referring to the markedly different role of auditory-motor experience in each case. The second highlights a phenomenon dubbed dual neural pathways, specifically that when a species with an existing vocal system evolves a new functionally distinct vocalization capability, it occurs through emergence of a second parallel neural pathway rather than through expansion of the extant circuitry. With these principles as a backdrop, we review evidence of acoustic modification of calling associated with background noise, conditioning effects, audience composition, and vocal convergence and divergence in nonhuman primates. Although each kind of evidence has been interpreted to show flexible cognitively mediated control over vocal production, we suggest that most are more consistent with affectively grounded mechanisms. The lone exception is production of simple, novel sounds in great apes, which is argued to reveal at least some degree of volitional vocal control. If also present in early hominins, the cortically based circuitry surmised to be associated with these rudimentary capabilities likely also provided the substrate for later emergence of the neural pathway allowing volitional production in modern humans.

The prioritization of voice fundamental frequency or formants in listeners' assessments of speaker size, masculinity, and attractiveness.

Key features of the voice--fundamental frequency (F(0)) and formant frequencies (Fn)--can vary extensively among individuals. Some of this variation might cue fitness-related, biosocial dimensions of speakers. Three experiments tested the independent, joint and relative effects of F(0) and Fn on listeners' assessments of the body size, masculinity (or femininity), and attractiveness of male and female speakers. Experiment 1 replicated previous findings concerning the joint and independent effects of F(0) and Fn on these assessments. Experiment 2 established frequency discrimination thresholds (or just-noticeable differences, JND's) for both vocal features to use in subsequent tests of their relative salience. JND's for F(0) and Fn were consistent in the range of 5%-6% for each sex. Experiment 3 put the two voice features in conflict by equally discriminable amounts and found that listeners consistently tracked Fn over F(0) in rating all three dimensions. Several non-exclusive possibilities for this outcome are considered, including that voice Fn provides more reliable cues to one or more dimensions and that listeners' assessments of the different dimensions are partially interdependent. Results highlight the value of first establishing JND's for discrimination of specific features of natural voices in future work examining their effects on voice-based social judgments.

Aping Language: Historical Perspectives on the Quest for Semantics, Syntax, and Other Rarefied Properties of Human Language in the Communication of Primates and Other Animals.

In 1980, Robert Seyfarth, Dorothy Cheney and Peter Marler published a landmark paper in Science claiming language-like semantic communication in the alarm calls of vervet monkeys. This article and the career research program it spawned for its authors catalyzed countless other studies searching for semantics, and then also syntax and other rarefied properties of language, in the communication systems of non-human primates and other animals. It also helped bolster a parallel tradition of teaching symbolism and syntax in artificial language systems to great apes. Although the search for language rudiments in the communications of primates long predates the vervet alarm call story, it is difficult to overstate the impact of the vervet research, for it fueled field and laboratory research programs for several generations of primatologists and kept busy an equal number of philosophers, linguists, and cognitive scientists debating possible implications for the origins and evolution of language and other vaunted elements of the human condition. Now 40-years on, the original vervet alarm call findings have been revised and claims of semanticity recanted; while other evidence for semantics and syntax in the natural communications of non-humans is sparse and weak. Ultimately, we are forced to conclude that there are simply few substantive precedents in the natural communications of animals for the high-level informational and representational properties of language, nor its complex syntax. This conclusion does not mean primates cannot be taught some version of these elements of language in artificial language systems - in fact, they can. Nor does it mean there is no continuity between the natural communications of animals and humans that could inform the evolution of language - in fact, there is such continuity. It just does not lie in the specialized semantic and syntactic properties of language. In reviewing these matters, I consider why it is that primates do not evince high-level properties of language in their natural communications but why we so readily accepted that they did or should; and what lessons we might draw from that experience. In the process, I also consider why accounts of human-like characteristics in animals can be so irresistibly appealing.

Asymmetries in the individual distinctiveness and maternal recognition of infant contact calls and distress screams in baboons.

A key component of nonhuman primate vocal communication is the production and recognition of clear cues to social identity that function in the management of these species' individualistic social relationships. However, it remains unclear how ubiquitous such identity cues are across call types and age-sex classes and what the underlying vocal production mechanisms responsible might be. This study focused on two structurally distinct call types produced by infant baboons in contexts that place a similar functional premium on communicating clear cues to caller identity: (1) contact calls produced when physically separated from, and attempting to relocate, mothers and (2) distress screams produced when aggressively attacked by other group members. Acoustic analyses and field experiments were conducted to examine individual differentiation in single vocalizations of each type and to test mothers' ability to recognize infant calls. Both call types showed statistically significant individual differentiation, but the magnitude of the differentiation was substantially higher in contact calls. Mothers readily discriminated own-offspring contact calls from those of familiar but unrelated infants, but did not do so when it came to distress screams. Several possible explanations for these asymmetries in call differentiation and recognition are considered.

Lifting the curtain on the Wizard of Oz: biased voice-based impressions of speaker size.

The consistent, but often wrong, impressions people form of the size of unseen speakers are not random but rather point to a consistent misattribution bias, one that the advertising, broadcasting, and entertainment industries also routinely exploit. The authors report 3 experiments examining the perceptual basis of this bias. The results indicate that, under controlled experimental conditions, listeners can make relative size distinctions between male speakers using reliable cues carried in voice formant frequencies (resonant frequencies, or timbre) but that this ability can be perturbed by discordant voice fundamental frequency (F-sub-0, or pitch) differences between speakers. The authors introduce 3 accounts for the perceptual pull that voice F-sub-0 can exert on our routine (mis)attributions of speaker size and consider the role that voice F-sub-0 plays in additional voice-based attributions that may or may not be reliable but that have clear size connotations.

Salience of caller identity in rhesus monkey (Macaca mulatta) coos and screams: perceptual experiments with human (Homo sapiens) listeners.

Recent evidence from acoustic analysis and playback experiments indicates that adult female rhesus monkey (Macaca mulatta) coos are individually distinctive but their screams are not. In this study, the authors compared discrimination of individual identity in these sounds by naive human listeners who judged whether 2 sounds had been produced by the same monkey or 2 monkeys. Each of 3 experiments using this same-different design showed significantly better discrimination of vocalizer identity from coos than from screams. Experiment 1 demonstrated the basic finding. Experiment 2 also tested the effect of non-identity-related scream variation, and Experiment 3 added a comparison with human vowel sounds. Outcomes suggest that acoustic structural differences in coos and screams influence salience of caller-identity cues, with significant implications for understanding the functions of these calls.

Visual kin recognition and family resemblance in chimpanzees (Pan troglodytes).

The male-offspring biased visual kin recognition in chimpanzees (Pan troglodytes) reported by L. A. Parr and F. B. M. de Waal (1999) was replicated with human (Homo sapiens) participants and a principal components analysis (PCA) of pixel maps of the chimpanzee face photos. With the same original materials and methods, both humans and the PCA produced the same asymmetry in kin recognition as found with the chimpanzees. The PCA suggested that the asymmetry was a function of differences in the distribution of global characteristics associated with the framing of the faces in the son and daughter test sets. Eliminating potential framing biases, either by cropping the photos tightly to the faces or by rebalancing the recognition foils, eliminated the asymmetry but not human participants' ability to recognize chimpanzee kin.

Parsing the role of consonants versus vowels in the classic Takete-Maluma phenomenon.

Wolfgang Köhler (1929, Gestalt psychology, New York, NY: Liveright) famously reported a bias in people's choice of nonsense words as labels for novel objects, pointing to possible naïve expectations about language structure. Two accounts have been offered to explain this bias, one focusing on the visuomotor effects of different vowel forms and the other focusing on variation in the acoustic structure and perceptual quality of different consonants. To date, evidence in support of both effects is mixed. Moreover, the veracity of either effect has often been doubted due to perceived limitations in methodologies and stimulus materials. A novel word-construction experiment is presented to test both proposed effects using randomized word- and image-generation techniques to address previous methodological concerns. Results show that participants are sensitive to both vowel and consonant content, constructing novel words of relatively sonorant consonants and rounded vowels to label curved object images, and of relatively plosive consonants and nonrounded vowels to label jagged object images. Results point to additional influences on word construction potentially related to the articulatory affordances or constraints accompanying different word forms.

Plasticity after perceptual narrowing for voice perception: reinstating the ability to discriminate monkeys by their voices at 12 months of age.

Differentiating individuals by their voice is an important social skill for infants to acquire. In a previous study, we demonstrated that the ability to discriminate individuals by voice follows a pattern of perceptual narrowing (Friendly et al., 2013). Specifically, we found that the ability to discriminate between two foreign-species (rhesus monkey) voices decreased significantly between 6 and 12 months of age. Also during this period, there was a trend for the ability to discriminate human voices to increase. Here we investigate the extent to which plasticity remains at 12 months, after perceptual narrowing has occurred. We found that 12-month-olds who received 2 weeks of monkey-voice training were significantly better at discriminating between rhesus monkey voices than untrained 12-month-olds. Furthermore, discrimination was reinstated to a level slightly better than that of untrained 6-month-olds, suggesting that voice-processing abilities remain considerably plastic at the end of the first year.

The sound of round: evaluating the sound-symbolic role of consonants in the classic Takete-Maluma phenomenon.

Köhler (1929) famously reported a bias in people's matching of nonsense words to novel object shapes, pointing to possible naïve expectations about language structure. The bias has been attributed to synesthesia-like coactivation of motor or somatosensory areas involved in vowel articulation and visual areas involved in perceiving object shape (Ramachandran & Hubbard, 2001). We report two experiments testing an alternative that emphasizes consonants and natural semantic distinctions flowing from the auditory perceptual quality of salient acoustic differences among them. Our experiments replicated previous studies using similar word and image materials but included additional conditions swapping the consonant and vowel contents of words; using novel, randomly generated words and images; and presenting words either visually or aurally. In both experiments, subjects' image-matching responses showed evidence of tracking the consonant content of words. We discuss the possibility that vowels and consonants both play a role and consider some methodological factors that might influence their relative effects. (PsycINFO Database Record (c) 2011 APA, all rights reserved).

The Queen's English: an alternative, biosocial hypothesis for the distinctive features of "gay speech".

Popular stereotypes concerning the speech of homosexuals typically attribute speech patterns characteristic of the opposite-sex, i.e., broadly feminized speech in gay men and broadly masculinized speech in lesbian women. A small body of recent empirical research has begun to address the subject more systematically and to consider specific mechanistic hypotheses to account for the potentially distinctive features of homosexual speech. Results do not yet fully endorse the stereotypes but they do not entirely discount them either; nor do they cleanly favor any single mechanistic hypothesis. To contribute to this growing body of research, we report acoustic analyses of 2,875 vowel sounds from a balanced set of 125 speakers representing heterosexual and homosexual individuals of each sex from southern Alberta, Canada. Analyses focused on voice pitch and formant frequencies which together determine the principle perceptual features of vowels. There was no significant difference in mean voice pitch between heterosexual and homosexual men or between heterosexual and homosexual women, but there were significant differences in the formant frequencies of vowels produced by both homosexual groups compared to their heterosexual counterparts. Formant frequency differences were specific to only certain vowel sounds and some could be attributed to basic differences in body size between heterosexual and homosexual speakers. The remaining formant frequency differences were not obviously due to differences in vocal tract anatomy between heterosexual and homosexual speakers, nor did they reflect global feminization or masculinization of vowel production patterns in homosexual men and women, respectively. The vowel-specific differences observed could reflect social modeling processes in which only certain speech patterns of the opposite-sex, or of same-sex homosexuals, are selectively adopted. However, we introduce an alternative biosocial hypothesis, specifically that the distinctive, vowel-specific features of homosexual speakers relative to heterosexual speakers arise incidentally as a product of broader psychobehavioral differences between the two groups that are, in turn, continuous with and flow from the physiological processes that affect sexual orientation to begin with.

Homoplasy, homology, and the perceived special status of behavior in evolution.

Evolutionary biologists tend to tread cautiously when considering how behavioral data might be incorporated into phylogenetic analyses, largely because of the preconception that behavior somehow constitutes a "special" set of characters that may be inherently more prone to homoplasy or subject to different selection regimes than those that operate on the morphological or genetic traits traditionally used in phylogenetic reconstruction. In this review, we first consider how the evolution of behavior has been treated historically, paying particular attention to why phylogenetic reconstruction has often failed to include behavioral traits. We then discuss, from a theoretical perspective, what reasons there are--if any--for assuming that behavioral traits should be more prone to homoplasy than other types of traits. In doing so, we review several empirical studies that tackle this issue head-on. Finally, we examine how behavioral features have been used to good effect in phylogenetic reconstruction. Our conclusion is that there seems to be little justification on theoretical grounds for assuming that behavior is in any way "special"--either particularly labile or particularly prone to exhibit high levels of homoplasy. Additionally, in reviewing historical perceptions of behavior and their links to conceptions of homology, we conclude that there is no compelling reason why behavior cannot be homologized or therefore why it should not prove phylogenetically informative. In subsequently considering several factors related to selection that influence the likelihood of homoplasy occurring in any trait system, we also found no clear trend predicting homoplasy disproportionately in behavioral systems. In fact, where studied, the degree of homoplasy seen in behavioral traits is comparable to that seen in other trait systems. Ultimately, there appear to be no grounds for dismissing behavior a priori from the class of phylogenetically informative characters.

Social brains, simple minds: does social complexity really require cognitive complexity?

The social brain hypothesis is a well-accepted and well-supported evolutionary theory of enlarged brain size in the non-human primates. Nevertheless, it tends to emphasize an anthropocentric view of social life and cognition. This often leads to confusion between ultimate and proximate mechanisms, and an over-reliance on a Cartesian, narratively structured view of the mind and social life, which in turn lead to views of social complexity that are congenial to our views of ourselves, rather than necessarily representative of primate social worlds. In this paper, we argue for greater attention to embodied and distributed theories of cognition, which get us away from current fixations on 'theory of mind' and other high-level anthropocentric constructions, and allow for the generation of testable hypotheses that combine neurobiology, psychology and behaviour in a mutually reinforcing manner.

Who cares who calls? Selective responses to the lost calls of socially dominant group members in the white-faced capuchin (Cebus Capucinus).

In many social mammals and birds, soft vocalizations are habitually produced during dispersed moving and foraging, the function being to maintain contact and regulate spacing between group members. In some species, much louder calls are given sporadically by specific individuals when they become separated from the group, or 'lost'. The function of these calls has seldom been specifically tested, particularly among social primates, but is often assumed to involve regaining contact with the group based on a combination of individually distinctive calls and antiphonal responses to them from within the group. To test these assumptions, we conducted research on two groups of white-faced capuchins (Cebus capucinus) in Costa Rica. We analyzed 82 bouts of 'lost' calls given by 13 different adult individuals when separated from the group and the antiphonal responses they elicited. Lost calls were individually distinctive and were answered in 35% of calling episodes. Answers were selective: dominant males and females were answered more than were subordinate callers of either sex. As a result, dominant callers relocated and returned to the group more quickly than did subordinate callers. We discuss the potential proximate motivations for, and ultimate benefits of, such selective answering of dominant group members.