External eye appearance across primate species is diverse in shape and colouration, yet we still ... more External eye appearance across primate species is diverse in shape and colouration, yet we still lack an explanation for the drivers of such diversity. Here we quantify substantial interspecific variation in eye shape and colouration across 77 primate species representing all extant genera of anthropoid primates. We reassess a series of hypotheses aiming to explain ocular variation in horizontal elongation and in colouration across species. Heavier body weight and terrestrial locomotion are associated with elongated eye outlines. Species living closer to the equator present more pigmented conjunctivae, suggesting photoprotective functions. Irises become bluer in species living further away from the equator, adding to existing literature supporting a circadian clock function for bluer irises. These results shift the current focus from communicative, to ecological factors in driving variation in external eye appearance in anthropoid primates. They also highlight the possibility that s...
Observing others’ emotions triggers physiological arousal in infants as well as in adults, reflec... more Observing others’ emotions triggers physiological arousal in infants as well as in adults, reflected in dilated pupil sizes. This study is the first to examine parents’ and infants’ pupil responses to dynamic negative emotional facial expressions. Moreover, the links between pupil responses and negative emotional dispositions were explored among infants and parents. Infants’ and one of their parent's pupil responses to negative versus neutral faces were measured via eye tracking in 222 infants (5‐ to 7‐month‐olds, n = 77, 11‐ to 13‐month‐olds, n = 78, and 17‐ to 19‐month‐olds, n = 67) and 229 parents. One parent contributed to the pupil data, whereas both parents were invited to fill in questionnaires on their own and their infant's negative emotional dispositions. Infants did not differentially respond to negative expressions, while parents showed stronger pupil responses to negative versus neutral expressions. There was a positive association between infants' and their parent's mean pupil responses and significant links between mothers’ and fathers’ stress levels and their infants’ pupil responses. We conclude that a direct association between pupil responses in parents and offspring is observable already in infancy in typical development. Stress in parents is related to their infants’ pupillary arousal to negative emotions.
Journal of the Acoustical Society of America, Sep 1, 2018
Laughter occurs across all great ape species, yet human laughter differs from that of other prima... more Laughter occurs across all great ape species, yet human laughter differs from that of other primates: Human laughter is primarily produced on the exhale, whereas other primates laugh on both the inhale and exhale. In the current study, we asked whether human infants laugh in a similar manner to apes, given that human infants, like non-human primates, tend to laugh in the context of tickling or rough-and-tumble play. Human adults, in contrast, laugh across many different kinds of social interactions. To test this hypothesis, we examined whether human infant laughter is acoustically more similar to non-human apes' laughter. Laughter clips from infants aged 3 to 18 months were annotated by phoneticians and evaluated by two listener samples (naïve listeners and phoneticians, respectively). The results provide support for the prediction that the proportion of infants’ laughter produced on the exhale increases with age. These results suggest that at younger ages, human infants’ laughter is more similar to that of other great apes. These findings are discussed in the context of vocal control maturation and social learning.
External eye appearance across primate species is diverse in shape and colouration, yet we still ... more External eye appearance across primate species is diverse in shape and colouration, yet we still lack an explanation for the drivers of such diversity. Here we quantify substantial interspecific variation in eye shape and colouration across 77 primate species representing all extant genera of anthropoid primates. We reassess a series of hypotheses aiming to explain ocular variation in horizontal elongation and in colouration across species. Heavier body weight and terrestrial locomotion are associated with elongated eye outlines. Species living closer to the equator present more pigmented conjunctivae, suggesting photoprotective functions. Irises become bluer in species living further away from the equator, adding to existing literature supporting a circadian clock function for bluer irises. These results shift the current focus from communicative, to ecological factors in driving variation in external eye appearance in anthropoid primates. They also highlight the possibility that s...
Observing others’ emotions triggers physiological arousal in infants as well as in adults, reflec... more Observing others’ emotions triggers physiological arousal in infants as well as in adults, reflected in dilated pupil sizes. This study is the first to examine parents’ and infants’ pupil responses to dynamic negative emotional facial expressions. Moreover, the links between pupil responses and negative emotional dispositions were explored among infants and parents. Infants’ and one of their parent's pupil responses to negative versus neutral faces were measured via eye tracking in 222 infants (5‐ to 7‐month‐olds, n = 77, 11‐ to 13‐month‐olds, n = 78, and 17‐ to 19‐month‐olds, n = 67) and 229 parents. One parent contributed to the pupil data, whereas both parents were invited to fill in questionnaires on their own and their infant's negative emotional dispositions. Infants did not differentially respond to negative expressions, while parents showed stronger pupil responses to negative versus neutral expressions. There was a positive association between infants' and their parent's mean pupil responses and significant links between mothers’ and fathers’ stress levels and their infants’ pupil responses. We conclude that a direct association between pupil responses in parents and offspring is observable already in infancy in typical development. Stress in parents is related to their infants’ pupillary arousal to negative emotions.
Journal of the Acoustical Society of America, Sep 1, 2018
Laughter occurs across all great ape species, yet human laughter differs from that of other prima... more Laughter occurs across all great ape species, yet human laughter differs from that of other primates: Human laughter is primarily produced on the exhale, whereas other primates laugh on both the inhale and exhale. In the current study, we asked whether human infants laugh in a similar manner to apes, given that human infants, like non-human primates, tend to laugh in the context of tickling or rough-and-tumble play. Human adults, in contrast, laugh across many different kinds of social interactions. To test this hypothesis, we examined whether human infant laughter is acoustically more similar to non-human apes' laughter. Laughter clips from infants aged 3 to 18 months were annotated by phoneticians and evaluated by two listener samples (naïve listeners and phoneticians, respectively). The results provide support for the prediction that the proportion of infants’ laughter produced on the exhale increases with age. These results suggest that at younger ages, human infants’ laughter is more similar to that of other great apes. These findings are discussed in the context of vocal control maturation and social learning.
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