‘Did I just do that?’ : Six-month-olds learn the contingency between their vocalisations and a visual reward in 5 minutes

It has been shown that infants can increase or modify a motorically available behaviour such as sucking, kicking, arm waving, etc., in response to a positive visual reinforcement (e.g., DeCasper & Fifer, 1980; Millar, 1990; Rochat & Striano, 1999; Rovee-Collier, 1997; Watson & Ramey, 1972). We tested infants to determine if they would also change their vocal behaviour in response to contingent feedback which lacks the social, emotional and auditory modelling typical of parent-child interaction. Here we show that in a single five-minute session infants increased the rate of their vocalisations in order to control the appearance of colourful shapes on an iPad screen. This is the first experimental study to demonstrate that infants can rapidly learn to increase their vocalisations when given positive reinforcement with no social element. This work sets the foundations for future studies into the causal relationship between the number of early vocalisations and the onset of words. In addition, there are potential clinical applications for reinforcing vocal practice in infant populations who are at risk for poor language skills.