Developmental Changes in Auditory-Evoked Alpha Activity Underlie the Increasing Precision With Which Infants Link Language and Cognition (WP-20-08)
Kali Woodruff Carr, Danielle Perszyk, Elizabeth Norton, Joel Voss, David Poeppel, and Sandra Waxman
Although communication is ubiquitous throughout the animal kingdom, the power and precision with which we link language to cognition is uniquely human. By 3-4 months of age, infants have already begun to establish this link: simply listening to human language facilitates infants’ success in fundamental cognitive processes including object categorization. This link derives from an initially broader set of signals that at 4 months includes the vocalizations of both humans and non-human primates (but not backwards speech), but by 6 months has been tuned to include only human language. This tuning is adaptive: infants increasingly focus in on the signals (language) that will ultimately constitute the foundations of meaning. But it remains unknown how these signals exert their cognitive advantage, and how infants’ responses become tuned within the first 6 months of life. The researchers propose that this early link between acoustic signals and cognition may be guided by a system that directs infants’ attention towards (or away from) key elements in their environment. To identify neurocognitive markers of infant attention, they collected EEG activity from 4- and 6-month-olds in response to three types of acoustic signals (infant-directed speech, backwards speech, and non-human primate vocalizations) to assess changes in alpha power, as alpha-band activity is a well-established index of infant attentional engagement. In 6-month-olds, alpha activity was modulated by both infant-directed speech and non-human primate vocalizations, the two signals that initially support cognition, but not by backward speech, a signal that fails to support cognition at any age. Moreover, human and nonhuman vocalizations modulated infants’ alpha activity in inverse ways, suggesting that infants draw upon attentional mechanisms either to sustain (for human speech) or to sever (for nonhuman primate vocalizations) their links between these signals and cognition.