Developmental psychobiology
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On the assumption that the ability to discriminate facial expressions has adaptive value to infants during early social exchanges, ethologically based theorists have argued that this ability is innate. Guided by this perspective, we investigated the ability of infants, 4-6 months old to recognize and discriminate facial expressions of anger, fear, and surprise. ⋯ These results suggest that infants can abstract configurations of features that give affective meaning to facial expressions. It is suggested that the differences in habituation to each expression might be the result of their distinct functional signification for the infant.
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The long-term effect of early mothering style on juvenile responsiveness to the external environment was studied in vervet monkeys living in two naturally composed, undisturbed social groups. Mothering behavior for 35 mother-infant dyads was analyzed by principal components analysis which revealed two independent dimensions: protectiveness and rejection. Protectiveness was characterized by high levels of approach, making contact, restraint, and inspection from mother to infant, and rejection was associated with high levels of rejection, breaking contact, and leaving. ⋯ They also took longer to enter a completely novel environment compared to juveniles who had had less protective mothers. Maternal rejection was not significantly associated with looking out or with latency to enter the novel environment. These results were independent of the effects of age, sex, and dominance rank on behavior.
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Adult song sparrows (Melospiza melodia) were tested for response to songs of conspecific males that had been reared in acoustic isolation or deafened early in life. Territorial males responded more aggressively to playback of songs of isolated males than to songs of deafened males but did not discriminate between songs of deafened males and heterospecific songs. Captive females showed an identical pattern when their response was measured in terms of the number and intensity of courtship displays evoked by song. The results support the auditory template theory of song development in demonstrating that species-identifying features are present in songs of isolates and in showing that males unable to hear their own song production do not incorporate these species-identifying features into their songs.
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To investigate the modifiability of the brown-headed female cowbird's (Molothrus ater ater) response to male song, we reared M.a. ater females with either M.a. ater or M.a. obscurus males, whose songs differ in geographic origin. The females were later tested for their responsiveness to playbacks of M.a. ater and M.a. obscurus song. Rearing with M.a. obscurus males had no effect on the female's preference for her native song variant, suggesting a closed program for receptive development. The data on song perception are contrasted with those previously obtained for male production and indicate different constraints on song perception as opposed to song production.
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The cardiac orienting response to species-specific songs was measured in young swamp sparrows and song sparrows. Swamp sparrows respond with significantly greater deceleration to conspecific songs than to songs of the sympatric song sparrow. This discriminatory ability is operating during the sensitive period for song learning and is evident upon initial exposures to conspecific song. These results are the 1st direct evidence for a sensory component in the process of selective vocal learning in birds.