1 The Basics: Framing the Foundation
Joan G. Hewitt and Jane R. Madell
Summary
This chapter discusses the importance of auditory brain development and details the framework for this book. Auditory stimulation is critical in infants to develop the auditory brain. If the brain is not stimulated with clear sounds, it will get reorganized and there will not be another opportunity to develop the auditory brain. If children do not have a clear auditory signal, we cannot expect them to have good listening or spoken language skills. It would be wrong to conclude that a child born deaf can use sign language during the early years and still develop synaptic connections and neural networks in the auditory cortex that will be sufficient to foster auditory and spoken language development. In addition to having technology that provides good auditory access, children need to be exposed to intelligible speech and complex, high-level models of spoken language. If a child hears fewer words, either because of inability to hear words or because of reduced auditory stimulation and input, language and IQ will be affected. Families must understand that they are their baby's primary teachers and carefully choose the communication option that will enable them to create a language-rich environment for their child. Clinicians must ensure that appropriate technology is fitted and that intervention begins at the appropriate language stage, not chronological age.
Keywords
neurobiological hearing loss, early identification, synaptic pruning, communication options
Key Points
Hearing loss in children is a neurological emergency.
Auditory stimulation is essential for building a child's auditory brain.
Early identification through newborn hearing screening, along with excellent technology, enables babies with hearing loss to learn with their typically hearing peers.
Listening experience in infancy is critical for development of speech and language, and a strong auditory base in language is essential for reading and learning.
The appropriate therapy starting point should be determined by a child's language level, not by chronological age.
Language is best learned through hearing. Therapy that is auditory-based will be the most successful in helping children with hearing loss develop speech, language, and literacy skills.
Families must understand that they are their baby's primary teachers.
All spoken language development follows one very specific process ("hearer" to "listener" to "understander" to "speaker").
1.1 Building a House
Have you ever watched a house being built? Although it takes considerable time and skill, master builders take great care to lay a firm foundation, and only after the foundation is determined to be solid do they begin the processes of framing, adding stories, creating rooms, and so forth. Similar to building a house, speech and language development in children is a lengthy process, and it is built upon the foundation of hearing. For babies who are born with hearing, the foundation naturally exists for listening, receptive language, and expressive language to be built. However, for babies born with hearing loss, the foundation-hearing-is not firm or does not exist. Thus, hearing is where we must start if the goal is to develop spoken language in children with hearing loss.
1.2 Why Hearing Is the Foundation for Speech and Language Development in Children
There is substantial neurobiological evidence that hearing is the most effective sensory modality for developing spoken language and cognitive skills.2,2,3,4,5,6,7 Children with typical hearing are born listening and have been listening for approximately 20 weeks in utero. They can recognize their mother's voice and can identify the important words in a sentence. In the first few months after birth a baby can discriminate various speech sounds. By their first birthday, babies' brains become reorganized so that they recognize speech sounds only in the language that they hear daily. By 6 months a child will recognize short phrases followed by familiar words, such as "Mommy has juice."8
In addition, hearing is the fastest sense. It gets information to the brain more rapidly than all the other senses. Moreover, while we can close our eyes and not see, we cannot close our ears; there are no "earlids." Thus, children with typical hearing are connected to their world through hearing 24 hours a day.
1.3 How Hearing Loss in Children Affects Speech and Language Development
Hearing loss in children is a neurological emergency. When a child is born with a hearing loss, that child has already had approximately 20 weeks of auditory deprivation in utero. Thus, time is of the essence. Hearing not only connects babies to the world around them, but the strong auditory base created by listening experience in infancy is essential for the development of language, which serves as the foundation for learning and reading (see Chapter 13). Even when children with hearing loss have appropriate technology, they still do not hear 24 hours a day. None of the technology available today is designed to be worn day and night. Nevertheless, the desire to connect auditorily to the world around us is so strong that parents often tell us their children want to keep hearing aids or cochlear implants on at night when they go to sleep.
So, for children with hearing loss, how do we start to frame the foundation?
1.4 Framing the Foundation: Current Research and Applications in Auditory Brain Development
Hearing occurs in the brain. Discussions about neurobiology of sensory input are really conversations about the brain. The brain is most plastic and has the most potential to create the detailed connections necessary when the child is youngest. Because the infant brain grows quickly, it is essential that we provide the infant's brain with good, clear auditory stimulation. In the absence of sound, the brain will reorganize itself. When the brain is stimulated with clear auditory signals, synapses develop to connect neurons to process those signals. If a part of the brain is not stimulated, the synapses that are not going to be used are eliminated from the neural pathways (synaptic pruning) so that the neurons can be put to some other use. While synaptic pruning occurs throughout the lifetime, the most significant synaptic pruning occurs during the first few years. If we do not provide clear auditory stimulation early, synaptic pruning in the auditory centers will occur, and the child will not get another opportunity to develop the auditory brain.9,10
For auditory stimulation, the ears are the doorway to the brain. Hearing loss interferes with sound reaching the brain by, essentially, closing the doorway to the brain. Technology, appropriately fitted, opens the closed doorway, enabling sound and spoken language inputs to reach the brain and develop the auditory pathways. The brain can only organize itself around the stimulation it receives. If it receives a complete auditory signal, the brain will be organized with detailed auditory connections. Research clearly shows that early identification of hearing loss and early fitting of technology can provide the essential early access to the brain that is critical for auditory learning.11,12,13,14 If the brain receives an incomplete signal because of hearing loss, the brain will be organized differently. If a child does not receive a clear signal, both receptive and expressive speech and language as well as literacy will be affected. How children hear is how we can expect them to talk: in Michael Merzenich's phrase, "muddy in, muddy out."15
Pearl
If we don't provide auditory stimulation early, we do not get an opportunity later to develop the auditory brain.
Pearl
The purpose of technology is to get auditory information to the brain.
1.5 What Happens If There Is No Frame: Auditory Deprivation
There are a significant number of studies exploring brain activity in children with and without hearing loss. Research has demonstrated that auditory stimulation results in responses in the auditory cortex. Hand movements demonstrate activity in the occipital cortex but not the auditory cortex.
While long-deafened adults who have not used technology and have used sign language may be able to identify some gross sounds after receiving a cochlear implant, they cannot identify open-set speech information. Long-duration unamplified or poorly amplified deafness results in reorganization of the auditory cortex such that connections never develop to enable a listener to interpret sound and spoken language meaningfully. If auditory input is not delivered to the auditory cortex, then it cannot be distributed to the rest of the brain for the higher-order processing necessary to convey a meaningful auditory experience. If the secondary auditory cortex is not stimulated early, the visual cortex will take over the neurons that normally make up the secondary auditory cortex.
It would be wrong to conclude that a child born deaf can use sign language during the early years and later develop synaptic connections and neural networks in the auditory cortex that will be sufficient to foster strong auditory and spoken language development. The sole use of visual forms of communication during the first few years of life without auditory language stimulation results in the appropriation...
