Does blindness influence trust? A comparative study on social trust among blind and sighted adults

Although blind individuals must often rely on others to navigate their physical environment, recent studies concerning differences between blind and sighted persons in attributing social traits to others based on nonvisual cues remain inconclusive. Here we examined whether blind and sighted individuals vary in their level of social trust in others. One hundred and twenty-four healthy men and women participated in the study, including 32 congenitally blind, 27 late blind, and 65 sighted adult controls. We measured levels of social trust represented by two independent convictions, that people are exploitative, or dishonest. Linear mixed models showed no significant differences between sighted, late blind and congenitally blind individuals, indicating that visual deprivation does not predict level of trust in others. For both blind and sighted participants, the belief that people are exploitative was stronger than the belief that people are dishonest

Women’s voice pitch lowers after pregnancy

Women’s voice pitch (the perceptual correlate of fundamental frequency, F0) varies across the menstrual cycle and lowers after menopause, and may represent a putative signal of women’s fertility and reproductive age. Yet, despite dramatic changes in women’s sex hormone levels and bodies during and after pregnancy, previous between-subject and case studies have not found systematic changes in F0 due to pregnancy. Here, we tracked within-individual variation in 20 mothers’ voices during their first pregnancy, as well as up to 5 years before conception and 5 years postpartum. Voice recordings from 20 age-matched nulliparous women were measured as a control. Linear Mixed Models indicated that F0 mean, range and variation changed significantly following pregnancy in mothers, controlling for age at time of recording, whereas we did not observe any F0 changes across corresponding timeframes in our sample of nulliparous controls. Mothers’ voices became significantly lower-pitched and more monotonous during the first year postpartum compared to during pregnancy or before. These F0 parameters did not decrease within-individuals over a 5-year period prior to conception above and beyond the effects of ageing. Although voice pitch decreased following pregnancy, mothers’ F0 parameters reverted after the first year postpartum, approaching pre-pregnancy levels. Our results demonstrate that pregnancy has a transient and perceptually salient masculinizing effect on women’s voices

Vocal communication of simulated pain

While evidence suggests that pain cries produced by human babies and other mammal infants communicate acoustic cues to pain intensity, whether the pain vocalisations of human adults also encode pain intensity, and which acoustic characteristics influence listeners’ perceptions, remains unexplored. Here, we investigated how trained actors communicated pain by comparing the acoustic characteristics of nonverbal vocalisations expressing different levels of pain intensity (mild, moderate, and severe). We then performed playback experiments to examine whether vocalisers successfully communicated pain intensity to listeners, and which acoustic characteristics were responsible for variation in pain ratings. We found that the mean and range of voice fundamental frequency (F0, perceived as pitch), the amplitude of the vocalisation, the degree of periodicity of the vocalisation, and the proportion of the signal displaying nonlinear phenomena all increased with the level of simulated pain intensity. In turn, these parameters predicted increases in listeners’ ratings of pain intensity. We also found that while different voice features contributed to increases in pain ratings within each level of expressed pain, a combination of these features explained an impressive amount of the variance in listeners’ pain ratings, both across (76%) and within (31-54%) pain levels. Our results show that adult vocalisers can volitionally simulate and modulate pain vocalisations to influence listeners’ perceptions of pain in a manner consistent with authentic human infant and nonhuman mammal pain vocalisations, and highlight potential for the development of a practical quantitative tool to improve pain assessment in populations unable to self-report their subjective pain experience

Efficacy in deceptive vocal exaggeration of human body size

How can deceptive communication signals exist in an evolutionarily stable signalling system? To resolve this age-old honest signalling paradox, researchers must first establish whether deception benefits deceivers. However, while vocal exaggeration is widespread in the animal kingdom and assumably adaptive, its effectiveness in biasing listeners has not been established. Here, we show that human listeners can detect deceptive vocal signals produced by vocalisers who volitionally shift their voice frequencies to exaggerate or attenuate their perceived size. Listeners can also judge the relative heights of cheaters, whose deceptive signals retain reliable acoustic cues to interindividual height. Importantly, although vocal deception biases listeners’ absolute height judgments, listeners recalibrate their height assessments for vocalisers they correctly and concurrently identify as deceptive, particularly men judging men. Thus, while size exaggeration can fool listeners, benefiting the deceiver, its detection can reduce bias and mitigate costs for listeners, underscoring an unremitting arms-race between signallers and receivers in animal communication

Seven and up: individual differences in male voice fundamental frequency emerge before puberty and remain stable throughout adulthood

Voice pitch (the perceptual correlate of fundamental frequency, F0) varies considerably even among individuals of the same sex and age, communicating a host of socially and evolutionarily relevant information. However, due to the almost exclusive utilization of cross-sectional designs in previous studies, it remains unknown whether these individual differences in voice pitch emerge before, during or after sexual maturation, and whether voice pitch remains stable into adulthood. Here, we measured the F0 parameters of men who were recorded once every 7 years from age 7 to 56 as they participated in the British television documentary Up Series. Linear mixed models revealed significant effects of age on all F0 parameters, wherein F0 mean, minimum, maximum and the standard deviation of F0 showed sharp pubertal decreases between age 7 and 21, yet remained remarkably stable after age 28. Critically, men's pre-pubertal F0 at age 7 strongly predicted their F0 at every subsequent adult age, explaining up to 64% of the variance in post-pubertal F0. This finding suggests that between-individual differences in voice pitch that are known to play an important role in men's reproductive success are in fact largely determined by age 7, and may therefore be linked to prenatal and/or pre-pubertal androgen exposure

Voice parameters predict sex-specific body morphology in men and women

Studies of several mammalian species confirm that formant frequencies (vocal tract resonances) predict height and weight better than does fundamental frequency (F0, perceived as pitch) in same-sex adults due to differential anatomical constraints. However, our recent meta-analysis (Pisanski et al., 2014, Animal Behaviour, 95, 89–99) indicated that formants and F0 could explain no more than 10% and 2% of the variance in human height, respectively, controlling for sex and age. Here, we examined whether other voice parameters, many of which are affected by sex hormones, can indicate additional variance in human body size or shape, and whether these relationships differ between the sexes. Using a cross-cultural sample of 700 men and women, we examined relationships among 19 voice parameters (minimum–maximum F0, mean F0, F0 variability, formant-based vocal tract length estimates, shimmer, jitter, harmonics-to-noise ratio) and eight indices of body size or shape (height, weight, body mass index, hip, waist and chest circumferences, waist-to-hip ratio, chest-to-hip ratio). Our results confirm that formant measures explain the most variance in heights and weights of men and women, whereas shimmer, jitter and harmonics-to-noise ratio do not indicate height, weight or body mass index in either sex. In contrast, these perturbation and noise parameters, in addition to F0 range and variability, explained more variance in body shape than did formants or mean F0, particularly among men. Shimmer or jitter explained the most variance in men's hip circumferences (12%) and chest-to-hip ratios (6%), whereas harmonics-to-noise ratio and formants explained the most variance in women's waist-to-hip ratios (11%), and significantly more than in men's waist-to-hip ratios. Our study represents the most comprehensive analysis of vocal indicators of human body size to date and offers a foundation for future research examining the hormonal mechanisms of voice production in humans and perceptual playback experiments

Human roars communicate upper-body strength more effectively than do screams or aggressive and distressed speech

Despite widespread evidence that nonverbal components of human speech (e.g., voice pitch) communicate information about physical attributes of vocalizers and that listeners can judge traits such as strength and body size from speech, few studies have examined the communicative functions of human nonverbal vocalizations (such as roars, screams, grunts and laughs). Critically, no previous study has yet to examine the acoustic correlates of strength in nonverbal vocalisations, including roars, nor identified reliable vocal cues to strength in human speech. In addition to being less acoustically constrained than articulated speech, agonistic nonverbal vocalizations function primarily to express motivation and emotion, such as threat, and may therefore communicate strength and body size more effectively than speech. Here, we investigated acoustic cues to strength and size in roars compared to screams and speech sentences produced in both aggressive and distress contexts. Using playback experiments, we then tested whether listeners can reliably infer a vocalizer’s actual strength and height from roars, screams, and valenced speech equivalents, and which acoustic features predicted listeners’ judgments. While there were no consistent acoustic cues to strength in any vocal stimuli, listeners accurately judged inter-individual differences in strength, and did so most effectively from aggressive voice stimuli (roars and aggressive speech). In addition, listeners more accurately judged strength from roars than from aggressive speech. In contrast, listeners’ judgments of height were most accurate for speech stimuli. These results support the prediction that vocalizers maximize impressions of physical strength in aggressive compared to distress contexts, and that inter-individual variation in strength may only be honestly communicated in vocalizations that function to communicate threat, particularly roars. Thus, in continuity with nonhuman mammals, the acoustic structure of human aggressive roars may have been selected to communicate, and to some extent exaggerate, functional cues to physical formidability

Voice pitch modulation in human mate choice

Inter-individual differences in human fundamental frequency (F0, perceived as voice pitch) predict mate quality and reproductive success, and affect listeners' social attributions. Although humans can readily and volitionally manipulate their vocal apparatus and resultant voice pitch, for instance, in the production of speech sounds and singing, little is known about whether humans exploit this capacity to adjust the non-verbal dimensions of their voices during social (including sexual) interactions. Here, we recorded full-length conversations of 30 adult men and women taking part in real speed-dating events and tested whether their voice pitch (mean, range and variability) changed with their personal mate choice preferences and the overall desirability of each dating partner. Within-individual analyses indicated that men lowered the minimum pitch of their voices when interacting with women who were overall highly desired by other men. Men also lowered their mean voice pitch on dates with women they selected as potential mates, particularly those who indicated a mutual preference (matches). Interestingly, although women spoke with a higher and more variable voice pitch towards men they selected as potential mates, women lowered both voice pitch parameters towards men who were most desired by other women and whom they also personally preferred. Between-individual analyses indicated that men in turn preferred women with lower-pitched voices, wherein women's minimum voice pitch explained up to 55% of the variance in men's mate preferences. These results, derived in an ecologically valid setting, show that individual- and group-level mate preferences can interact to affect vocal behaviour, and support the hypothesis that human voice modulation functions in non-verbal communication to elicit favourable judgements and behaviours from others, including potential mates

The pitch of babies’ cries predicts their voice pitch at age five

Voice pitch (fundamental frequency, F0) is a key dimension of our voice that varies Voice pitch (fundamental frequency, F0) is a key dimension of our voice that varies before and after puberty. While a recent longitudinal study indicates that inter-individual differences in voice pitch remain stable in men during adulthood and may even be determined before puberty [1], whether these differences emerge in infancy remains unknown. Here, using a longitudinal study design, we investigate the hypothesis that inter-individual differences in F0 are already present in the cries of pre-verbal babies. While based on a small sample (n = 15), our results indicate that the F0 of babies’ cries at 4 months of age may predict the F0 of their speech utterances at 5 years of age, explaining 41% of the inter-individual variance in voice pitch at that age in our sample. We also found that the right-hand ratio of the length of their index to ring finger (2D:4D digit ratio), which has been proposed to constitute an index of prenatal testosterone exposure, was positively correlated with F0 at both 4 months and 5 years of age. These findings suggest that a substantial proportion of between-individual differences in voice pitch, which convey important biosocial information about speakers, may partly originate in utero and thus already be present soon after birth

Human listeners can accurately judge strength and height relative to self from aggressive roars and speech

While animal vocalisations and human speech are known to communicate physical formidability, no previous study has examined whether human listeners can assess the strength or body size of vocalisers relative to their own, either from speech or from nonverbal vocalisations. Here, although men tended to underestimate women’s formidability, and women to overestimate men’s, listeners judged relative strength and height from aggressive roars and aggressive speech accurately. For example, when judging roars, male listeners accurately identified vocalisers who were substantially stronger than themselves in 88% of trials, and never as weaker. For male vocalisers only, roars functioned to exaggerate the expression of threat compared to aggressive speech, as men were rated as relatively stronger when producing roars. These results indicate that, like other mammals, the acoustic structure of human aggressive vocal signals (and in particular nonverbal roars) may have been selected to communicate functional information relevant to listeners’ survival