Abstract
The power of human language derives not only from the precision of its signal or the complexity of its grammar, but also from its links to cognition. Infants as young as 3 months have begun to link language and core cognitive capacities. At 3 and 4 months, this link is not exclusive to human language: listening to vocalizations of nonhuman primates also supports infant cognition. By 6 months, infants have tuned this link to human speech alone. Here we provide evidence that infants’ increasing precision in speech perception shapes which signals they will link to cognition. Infants listening to German, a nonnative language that shares key rhythmic and prosodic properties with their own native language (English), successfully formed object categories. In contrast, those listening to Cantonese, a language that differs considerably in these suprasegmental properties, failed. This provides the first evidence that infants’ increasingly precise perceptual tuning to the sounds of their native language sets constraints on the range of human languages they will link to cognition: infants begin to specify which human languages they will link to core cognitive capacities even before they sever the link between nonhuman primate vocalizations and cognition.
Highlights
Language is a signature of our species
When each image is paired with a segment of human language, infants as young as 3 months successfully form object categories; when the very same images are paired with tone sequences or a segment of backward speech, infants fail to do so[2,8]
Does listening to Cantonese boost infant categorization? In Experiment 2, infants participated in the same object categorization task as in Experiment 1, but this time each familiarization image was presented in conjunction with a segment of infant-directed Cantonese. These infants devoted the same amount of attention to the familiarization objects as their counterparts listening to German (p > 0.05), they failed to form object categories, showing no preference for either the novel or familiar object at test (Mnovelty preference = 0.51, SDnovelty preference = 0.15; t(37) = 0.38, p = 0.71, Cohen’s d = 0.067) (Fig. 1). Their chance-level test performance www.nature.com/scientificreports stands in sharp contrast to the success of their age-mates listening to either German, English[2], or nonhuman primate vocalizations[8] at 3–4 months
Summary
Language is a signature of our species. It enables us to express the contents of our own minds and to influence the minds of others. Language is not the only signal that boosts infant cognition at 3–4 months: listening to the vocalizations of nonhuman primates (blue-eyed Madagascar lemur; Eulemur macaco flavifron) supports object categorization[8] This suggests that at 3–4 months, infants have a broad initial template that permits them to link the vocalizations of both humans and nonhuman primates to core conceptual capacities. The cognitive advantage conferred by listening to nonhuman primate vocalizations is short-lived: by 6 months, nonhuman primate vocalizations no longer support object categorization[8] This evidence offers new insights into the developmental mechanisms by which infants begin to establish an abstract link between language and cognition. Does infants’ increasing sensitivity to various acoustic features of language—namely, those that demark their native language—guide them to link some languages, but not others, to core conceptual processes?
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