Cochlear implants allow profoundly deaf infants to hear speech, which, with proper auditory therapy, allows them to learn spoken language. However, this new study from cognitive psychologist Derek M Houston, PhD, associate professor of otolaryngology at Indiana University School of Medicine shows that the children receiving the implants don’t automatically know how to listen when people speak to them.
Research presented at the recent Acoustical Society of America research meeting showed that deaf babies with cochlear implants spent the same amount of time “listening” as normal-hearing infants of the same age. However, these children with implants spent less time listening than younger normal-hearing infants who had the same amount of hearing experience. Dr Houston said,
When infants are born deaf, their development is shaped by a silent world. They learn to tune into the sights, smells, and touches that are relevant to them in their environment – but not the sounds. When they receive a cochlear implant, their world changes and is filled with sounds. But for these infants who have already begun to adapt to their silent environment, sounds may not – at least at first – be perceived as relevant to them.
It has been well-established that infants will look longer at a simple display – the checkerboard pattern – when hearing something they are interested in. I measured their ‘looking time’ at the pattern when it was paired with a repeating speech sound, and compared that to the looking time at the same pattern with no sound.
Houstons’ research revealed children with cochlear implants spent less time looking at the checkerboard pattern than children who could hear from birth. In addition, two years after implantation, children who were less attentive to speech early-on performed more poorly on a word recognition task. In other words, these infants and toddlers may hear the sounds around them, but not have any motivation to focus on them, which slows their ability to learn speech… And this can be traced for years through word recognition testing.
Furthermore, this research goes towards explaining why prelingually deafened children and adults have not developed a sense of danger to environmental warning signals: For example, they may hear a car horn while crossing a street, but it does not register in their brain properly, i.e. it does not trigger the instinctive danger reflex.
An abstract of Dr Houstons’ research is available at http://asa.aip.org/web2/asa/abstracts/search.may11/asa220.html
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