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Abstract Five mothers of squirrel monkey infants isolated from other species members were muted by severence of their vocal cords during pregnancy. After delivery, mother infant pairs were brought up in an environment free of any species-specific auditory input. One of these infants underwent a deafening operation five days after birth. In addition, two infants grew up under normal conditions, i.e., exposed to species-specific vocalization. Supplemental data were acquired from six other infants, four of them normally raised and two handraised. Soundspectrograms were taken over a period up to six months in the case of the isolates and up to 17 months for the normal animals. Samples of this spectrographical material were analyzed with respect to the form of calls and to quantitative criteria, such as duration, starting frequency, mid-frequency, and end frequency of peep and cackle calls. Clear evidence is presented that the vocal repertoire of squirrel monkey infants raised under normal conditions and those raised in the absence of species-specific auditory input are virtually identical. Furthermore, comparison of the infants' vocalization with those of adult animals shows no significant differences.
Winter et al. (Mon,) studied this question.