Washington, Oct 23 (IANS): The repetitive babbles of babies primarily are motivated by the infants' ability to hear themselves, shows a US study.

"Hearing is a critical aspect of infants' motivation to make early sounds," said study author Mary Fagan, an assistant professor of communication science and disorders in the University of Missouri-Columbia School of Health Professions.

"The fact that they attend to and learn from their own behaviours, especially in speech, highlights how infants' own experiences help their language, social and cognitive development," she added.

This research, Fagan said, does not diminish the importance of the speech that babies hear from others.

"We know they need to learn from others -- but it raises our awareness that infants are not just passive recipients of what others say to them. They are actively engaged in their own developmental process," Fagan said.

Fagan studied the babbles of 27 hearing infants and 16 infants with profound hearing loss before and after they received cochlear implants, which are small electronic devices embedded into the bone behind the ear that replace some functions of the damaged inner ear.

Before receiving cochlear implants, babies with profound hearing loss rarely produced repetitive vocalisations, such as 'ba-ba' or 'da-da.'

Within a few months of receiving cochlear implants, the number of babies who produced repetitive vocalisations increased, the number of vocalisations that contained repetitive syllables increased, and the number of actual repetitions in the string, such as 'ba-ba-ba-ba-ba,' increased, Fagan said.

"The research tells us that infants are motivated by hearing the sounds they produce, so these sounds are functional in some way," she said.