Experience is Instrumental in Tuning a Link Between Language and Cognition: Evidence from 6- to 7- Month-Old Infants' Object Categorization

Summary

At 3-4 months, listening to human and nonhuman primate vocalizations boosts infants' cognition; by 6 months, only human vocalizations exert this cognitive advantage. We describe an exposure manipulation that reveals the powerful shaping role of experience as infants specify which sounds to link to cognition and which to tune out.

Abstract

At birth, infants not only prefer listening to human vocalizations, but also have begun to link these vocalizations to cognition: For infants as young as three months of age, listening to human language supports object categorization, a core cognitive capacity. This precocious link is initially broad: At 3 and 4 months, vocalizations of both humans and nonhuman primates support categorization. But by 6 months, infants have narrowed the link: Only human vocalizations support object categorization. Here we ask what guides infants as they tune their initially broad link to a more precise one, engaged only by the vocalizations of our species. Across three studies, we use a novel exposure paradigm to examine the effects of experience. We document that merely exposing infants to nonhuman primate vocalizations enables infants to preserve the early-established link between this signal and categorization. In contrast, exposing infants to backward speech — a signal that fails to support categorization at any age — offers no such advantage. Our findings reveal the power of early experience as infants specify which signals, from an initially broad set, they will continue to link to cognition.

Introduction

Human infants are born ready to acquire language, a cultural and cognitive tool that defines us as a species and fundamentally shapes our development. Central to our capacity for learning language are two unique features of human development: Our altriciality and our powerful learning strategies. Together, these features unlock a remarkable degree of early plasticity that enables infants to be highly attuned to input from their environments. For example, although infants come into the world with a set of perceptual preferences and discriminatory capacities sufficiently broad to include the faces and voices of human and nonhuman primates, within months ....

Protocol

The following procedures were approved by the Northwestern University Institutional Review Board and informed consent was obtained from the caregivers of all infants. We recruited infants being raised in environments with more than 50% exposure to English^11,17. Infants in all experiments first listened to a soundtrack in which we manipulated their exposure to either lemur vocalizations or backward speech; they then participated in an object categorization task. What varied across infants was (a) the kind of signal they heard in the exposure manipulation and the categorization task (either lemur vocalizations o....

Results

Using the procedures outlined above (Figure 1), we ran three experiments to test the effects of exposure as infants refine the links between certain sounds and cognition.

Results of Experiment 1 revealed that brief exposure to lemur vocalizations had a striking effect. Seven month-olds exposed to lemur vocalizations reliably preferred the novel test image, M = 0.57, SD = 0.09; t(13) = .......

Discussion

Here we outline a procedure for examining the role of experience in linking sounds and core cognitive processes early in infancy. Our combined experiments document the first evidence that experience plays a central role in guiding infants to specify which signals, from a broad initial set of possibilities, they will harness to core conceptual processes that ultimately provide the foundations of meaning. They also reveal an intricate interface between nature and nurture: Although experience plays little role, if any, in d.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Laptop 1			Use for presenting exposure soundtrack; preferably using iTunes Visualizer
Laptop 2			Use for programming and presenting categorization task
Laptop 3 (optional)			Use for coding infant looking behavior (can also use one of the above laptops)
Coding software	SuperCoder		Use for coding infant looking behavior
Video recorder			Use for recording infants' face (looking behavior during categorization task)
Mixer			Use for integrating information from the video recorder (infant looking behavior) and the visual stimuli (categorization task)
DVD player			Use for recording the input from the video recorder (infant looking behavior)
Television			Use for viewing input from mixer (screen-in-screen; categorization task in corner of screen showing infant looking behavior)
Projector			Use for projecting visual stimuli of categorization task on screen
Speakers			Use for presenting auditory stimuli during categorization task
Blacked-out sunglasses			Use for blocking caretaker's vision during categorization task
Statistical analysis software	R		Use for analyzing infant looking behavior