Nonhuman primate vocalizations support categorization in very young human infants

Abstract

Language is a signature of our species and our primary conduit for conveying the contents of our minds. The power of language derives not only from the exquisite detail of the signal itself but also from its intricate link to human cognition. To acquire a language, infants must identify which signals are part of their language and discover how these signals are linked to meaning. At birth, infants prefer listening to vocalizations of human and nonhuman primates; within 3 mo, this initially broad listening preference is tuned specifically to human vocalizations. Moreover, even at this early developmental point, human vocalizations evoke more than listening preferences alone: they engender in infants a heightened focus on the objects in their visual environment and promote the formation of object categories, a fundamental cognitive capacity. Here, we illuminate the developmental origin of this early link between human vocalizations and cognition. We document that this link emerges from a broad biological template that initially encompasses vocalizations of human and nonhuman primates (but not backward speech) and that within 6 mo this link to cognition is tuned specifically to human vocalizations. At 3 and 4 mo, nonhuman primate vocalizations promote object categorization, mirroring precisely the advantages conferred by human vocalizations, but by 6 mo, nonhuman primate vocalizations no longer exert this advantageous effect. This striking developmental shift illuminates a path of specialization that supports infants as they forge the foundational links between human language and the core cognitive processes that will serve as the foundations of meaning.

Infants Associate Praise and Admonishment with Fair and Unfair Individuals

“…Conversely, 18-month-olds looked longer to the canine facial expression that mismatched the vocalizations. Similar transitions have been seen in younger infants with simpler stimuli (e.g., Ferry, Hespos & Waxman, 2013). …”

Labels Direct Infants’ Attention to Commonalities during Novel Category Learning

“…Using screen-based presentation of animal pictures, those findings were extended to age groups as young as 3 to 4 months [16], [19]. Although for very young infants facilitation was also achieved using primate vocalizations instead of labels [20], the effect appears to be specific to speech-like stimuli by 6 months [21], [22], [16]. In contrast, unsystematic labeling with different words did not cause any facilitation effects [23].…”

Listen up! Speech is for thinking during infancy

“…But infants’ preferences cannot tell us whether (or when) infants begin to link speech to the objects and events around them. A series of experiments designed to tackle this question focused on object categorization–a building block of cognition [13,14]. In these experiments, infants ranging in age from 3 to 12 months viewed several images from one object-category (e.g., dinosaurs), each accompanied by either a segment of speech or a sequence of sine-wave tones.…”

“…Moreover, this link, evident at three months, derives from a broader template that initially encompasses human speech as well as the calls of non-human primates (Madagascar blue-eyed lemurs: Eulemur macaco flavifrons) . Three- and 4-month-old infants’ categorization in the context of hearing lemur calls mirrors precisely their categorization in response to human speech; by 6 months, the link to categorization has become tuned specifically to human vocalizations [13]. This documents a surprisingly early link between human language and core cognitive processes, including object categorization that cannot be attributed to familiarity.…”