Dispelling the Myths of Auditory Deprivation
Ripper, Jessica, Volta Voices
Science is about discovery. Every day, more than 145,000 scientists walk out their front doors and arrive at jobs designed to expand human understanding of our world.
They're the myth busters who help the rest of us make sense of complex concepts such as climate change, nanotech fabrication or how the brain makes sense of speech and language.
That's where Dr. Anu Sharma comes in. Sharma and her colleagues have set their sights on improving our understanding of how auditory deprivation affects the development, deterioration and plasticity of the human auditory system. They're also examining the degree to which interventions with hearing technology can help.
In turn, the research conducted by Sharma and other scientists fuels the work of Dr. Melody Harrison, a professor of speech and hearing sciences who teaches neuroanatomy and is a specialist in early intervention.
Through their individual work, Sharma and Harrison are helping to dispel some common (and some not so common) myths about the importance of early auditory stimulation to children with hearing loss who are learning to listen and talk.
Myth #1: Babies' brains are primed for learning speech and language.
Most babies are born with brains primed for learning language, yet auditory deprivation can permanently alter how a child processes sound. Children generally learn language by hearing and attaching meaning to it long before they begin to speak, and stimulation of the central auditory pathways plays a vital role in helping them to understand sounds that they later learn to replicate. Children who are deaf and hard of hearing miss out on the sound stimulation that typically triggers the development of those auditory pathways, thereby hindering normal speech and language development.
Similarly, children who are born premature show different results on common tests such as the auditory brainstem response, or ABR, because their brains have not fully formed before birth. Harrison described a fetal brain as "being relatively smooth at the sixth month ... in the last three months before birth, it grows and develops very rapidly, filling the cranium so completely that folds and grooves develop to accommodate all the tissue." In contrast, the brains of babies born prematurely often have a smooth surface because the neural material has not had time to finish forming, potentially affecting speech and language learning.
Myth #2: It doesn't matter how old children are when they get hearing aids or cochlear implants.
Although central auditory pathways continue to grow and change during the first 20 years of life, Sharma's research confirms that there is a critical time window for stimulating auditory pathways to the brain. For children with hearing loss, early and regular use of hearing aids or cochlear implants can help them to develop speech and language skills comparable to their peers with typical hearing.
Sharma's studies used cortical auditory evoked response tests, a non-invasive technique that records brain waves in response to clicks or tones, which were conducted as children watched a movie of their choice. Newborns with typical hearing showed an initial latency of 300 milliseconds in response time; by age 3, latency had decreased significantly to a norm of approximately 125 milliseconds.
A corresponding study of 245 children with congenital deafness who had used cochlear implants for a minimum of six months showed great variability in the latency of their brains' responses based on the age they received their implants. Children who received implants after being deprived of sound for more than seven years showed latencies well above the norm. In contrast, nearly all the children who experienced less than three and a half years of auditory deprivation - the critical window of time for brain plasticity - achieved latencies that corresponded to children with typical hearing within three to six months. …