Deafness, Language Development, and Learning: What Does the Science Tell Us?

The issue

Through research, we know a great deal about the nature of hearing loss, brain development, language acquisition, and learning.  So what are the practical implications of what we have discovered?   How can we develop strategies for the successful education of deaf and hard-of-hearing children based upon this science?

What we know

The evaluation of newborns for their ability to detect sound identifies those who are deaf, or hard of hearing.  Further testing by persons trained in hearing evaluation (audiologists) can determine:
  • The degree of hearing loss, either mild to moderate (“hard of hearing”) or severe to profound (“deaf”).
  • Whether the loss is because of a lack of function of the cochlea and/or the auditory nerve (sensorineural hearing loss), or whether the problem results from the inability to conduct sound from the eardrum to the cochlea (conductive hearing loss).
  • Whether there is a physical abnormality of the inner ear organ of hearing and balance (the cochlea).  This can be done with a CT scan, and is important prior to planning for a cochlear implant.

During the first few years of life, the brain undergoes very rapid development.  We know that specific regions of the brain respond to specific stimuli (language, for example), and different regions have specific functions. This is referred to as brain localization or modularity of function.  Imaging studies (like MRIs) show that the same regions of the brain are involved with any language regardless of whether it is aural (spoken/heard) or visual (signed/seen).  Further, such studies also show that the early use of any language, spoken or signed, enhances brain development of the specific regions involved with language.  This early language ultimately promotes better communication and learning over the longer term.  Because cochlear implants are not presently an option during the first year of life in the United States, the use of sign language can be important for promoting brain development for later spoken language acquisition.

Speech-language professionals and educators employ different techniques to help children with hearing loss.  If the hearing loss is moderate, sound amplification through hearing aids and FM systems enhance language acquisition and learning. For those with profound hearing losses, a cochlear implant can transmit sound more directly to the auditory nerve compared to a hearing aid.  Cochlear implantation usually eliminates any “natural,” remaining hearing in the ear, but creates a new ability to detect sound.  Studies suggest that cochlear implants significantly enhance language acquisition and learning in 70-80% of children who are profoundly deaf.

What we don’t know

We don’t know how to determine early on whether (1) hearing aids or cochlear implantation or (2) sign language, spoken language (or both) will be the best for any individual child.  We do not yet know enough about the ultimate outcomes of each method or combination of methods.  This is a major focus of current research. Completing long-term studies of outcomes is difficult, because the population of deaf children is relatively small, and following many in long-term studies is difficult.   We expect to learn more about how the brain works in deaf children from more advanced research techniques such as functional MRI imaging.

Implications

It is important to diagnose the type and severity of hearing loss as early as possible. This guides the design of successful strategies for acquisition of communication skills, language acquisition, and learning.  For example, children with profound sensorineural hearing loss benefit most from cochlear implants.  For less severe conductive hearing loss, hearing aids may be more appropriate.  For some, a combination of techniques may be best.

The brain develops most rapidly during the first few years of life. During this period, the earlier the introduction of any language the better the brain develops capacity for language acquisition and communication.  Intervention during this early period is critical for enhancing the child’s ability to acquire language.

The brain changes with both physical maturation and educational experiences.  This is called brain plasticity.  The brain alters anatomically by continually developing new connections.  But, the progress is not always linear and predictable.  This means that the child’s individual education plan (IEP) needs regular, periodic review and alteration by educational professionals and parents if necessary.  Frequent re-evaluation is critically important for deaf and hard of hearing children.  Continual tailoring of the IEP to a child’s current needs creates the most enabling environment for learning and social integration.

Posted on July 10, 2017 by
J. Robert Kirkwood, MD
Baystate Medical Center and
Tufts University, School of Medicine (Retired)
kirkwoodjr {at} aol.com

 

Further reading