The effects of sign language on spoken language acquisition in children with hearing loss: a systematic review protocol

Population-based newborn hearing screening has become a standard of care in the developed world to improve the developmental outcomes for children with permanent hearing loss [1–3]. Childhood hearing loss is one of the most common congenital disorders affecting 1 to 3 per 1000 live births [3–5] resulting in 1,000 to 1,200 affected children born in Canada annually [6]. Hearing loss interferes with typical language acquisition and children are at risk of developing sub-optimal spoken language, and consequently poorer academic and literacy skills, than their peers with normal hearing [7–10]. While there is good evidence that newborn screening achieves early identification of hearing loss, the evidence for the effectiveness of screening in improving spoken language outcomes has been less convincing [2, 11–13]. It is well recognized that early identification is not sufficient to improve communication skills and that intervention using hearing prostheses and early language stimulation must follow [1, 14].

Historically, there has been a debate about what constitutes desirable outcomes for children with hearing loss and a plethora of intervention/education programs have evolved. These programs can be grouped into two distinct philosophies: one focused on fostering spoken language development and inclusion with normal hearing peers; and the other on communication using primarily a visual approach (for example, sign language) and promoting a sense of identity with a Deaf culture [15, 16]. Epidemiologic data confirm that more than 90% of children with hearing impairment are born to families where both parents have normal hearing [17]. Although there is generally a consensus that various treatment options with different outcome goals should be available to children and families, data from the Ministry of Child and Youth Services in Ontario (personal communication), where the first province-wide universal screening program was implemented in 2002, indicate that more than 90% of families choose a spoken language option for their children. This review will therefore address the issue of interventions aimed at developing spoken language outcomes and will not deal with philosophical differences that exist between various stakeholders involved in supporting children with hearing loss and their families.

Despite a growing body of evidence that children with hearing loss can develop oral language skills [9, 18, 19], there have been longstanding disagreements about optimal interventions when spoken language development is the desired outcome [20]. Although there is substantial and variable anecdotal evidence supporting various intervention approaches, there is little scientifically based consensus. However, this information is necessary to: 1) guide families in making decisions about care for their children in infancy; 2) inform clinicians so that they can design and tailor treatment plans to achieve the desired outcomes; and 3) inform policy makers so they can make decisions about investments in early intervention services.

From a theoretical perspective, research in neuroplasticity and critical periods of learning [21, 22] lend support to the theory that optimal intervention involving rich auditory and oral language stimulation should be initiated in infancy to mitigate the effects of hearing loss [23–25]. The expectation then is that oral language outcomes of children receiving auditory-based intervention should be better than those of children who are deprived of this intensive auditory stimulation through the addition of visual information which might slow down or interfere with spoken language acquisition. Another body of research suggests that signed languages such as American Sign Language (ASL) are processed in the brain in the same manner as spoken languages, are therefore complementary, and provide a strong foundation for learning oral languages [26, 27]. Applying this reasoning, associations such as the Bilingual Coalition of Canada have called for access to ASL for all children with hearing loss even when parents choose spoken language as the desired mode of communication for their child.

Further complicating the issue for parents is the growth of the use of signs, commonly known as “baby sign language” with typically developing babies. This practice raises further questions about whether the addition of signs might promote spoken language acquisition in children with impaired hearing. A systematic review [28] found no evidence supporting the use of baby signs or any indication that exposure to baby signs interfered with children’s typical language acquisition. Recently, the American Academy of Pediatrics concluded that baby sign language is a tool for improving communication in young children with normal hearing [29].

The uncertainty surrounding the most appropriate interventions required to achieve age-appropriate language skills is one of the major challenges facing newborn hearing screening initiatives. This review is timely because there has been a proliferation of newborn hearing screening programs worldwide in the past 10 years. In addition to early identification, early cochlear implantation “which involves electrical stimulation of the auditory system” has had a dramatic impact on improving the spoken language potential for children with severe to profound deafness. There is good evidence for positive spoken language outcomes from the cochlear implant literature [18, 25, 30] but considerable debate continues about what constitutes optimal intervention approaches for promoting spoken language acquisition, regardless of degree of hearing loss. In essence, the new possibilities for children due to newborn hearing screening, new technologies, and emerging evidence on using signs with normal hearing children have re-ignited the debate on best practices for children with hearing loss. Parents are therefore faced with important decisions in the early months of their child’s life when they first learn of the presence of permanent hearing loss.

Accordingly, the primary purpose of this research is to connect researchers and knowledge users to examine the evidence for the effects of various treatment options for early-identified children with hearing loss when the desired outcome is spoken communication. The major question addressed in this proposal is specific to the components or characteristics of the intervention and the auditory and spoken language capacity of the developing child. A review undertaken in 2008 to update the United States Preventive Services Task Force recommendations on newborn hearing screening highlighted the need for further research to demonstrate the effectiveness of the entire process of screening to intervention [2].

In 2002, as Ontario was implementing newborn hearing screening, a review commissioned by Health Canada [31] compared outcomes for various interventions across the spectrum from oral to sign language approaches but failed to find conclusive evidence, citing study quality as an important barrier to knowledge synthesis in the field. Since this 10-year old Health Canada review, technology has dramatically impacted pediatric hearing care such that early intervention for all children and early cochlear implantation (including recently the use of bilateral implants) to treat the most severe losses have become the new standards of care. Several new studies investigating the impact of newborn hearing screening outcomes and of early cochlear implantation have been published since the 2002 review.

Infant hearing screening continues to occupy an important place on national and international agendas as a population health intervention aimed at improving communication development for children with permanent hearing disorders. Hearing screening has received widespread support on the basis of the burden of the disorder to society and the assumption that early intervention can prevent or reduce delays in language development. However, there remains considerable uncertainty and disagreement about what constitutes optimal treatments for the current generation of early-identified children with hearing loss. Successful implementation of evidence into the pediatric hearing field has been difficult to achieve with the end result that unbiased information is not readily available to parents. Consequently, parents are forced to make decisions about care based on unclear and potentially biased evidence when their children are diagnosed in infancy.

This systematic review aims to become an important information tool for parents, clinicians, researchers, and decision-makers who need new evidence that is accumulating in the field of newborn screening and early intervention outcomes. Our goal is that this review will contribute to a better understanding of treatment effects, leading potentially to a timelier introduction of the most effective interventions that are aligned with parents’ desired outcomes for their children with hearing loss. Through a knowledge-user and researcher partnership, we will create a common understanding of the goals, use a common terminology, and assemble the best possible evidence to provide care to the “new” populations of children with early-identified hearing loss.

This review was motivated by questions and concerns at the clinical practice level of providing services for young children. One potential byproduct of this review is the development of clear research needs for the scientific community grounded in the experiences of the knowledge users. In the long-term, we envision that the findings resulting from this collaboration that spans healthcare, education, and graduate training will help to further define appropriate questions for future collaborative research to address childhood hearing loss issues in a field wrought with anecdotal reports and expert opinion. Accordingly, this review is expected to provide a foundation for ongoing and new scientific enquiry to more effectively assist families affected by childhood hearing loss and to optimize health services.

EMF is Associate Professor in the Audiology and Speech-Language Program, Faculty of Health Sciences at the University of Ottawa and Senior Scientist at the Children’s Hospital of Eastern Ontario Research Institute. AS is Senior Clinical Research Associate, Knowledge Synthesis Group, Centre for Practice-Changing Research, Ottawa Hospital Research Institute. CG is Senior Research Program Manager, Knowledge Synthesis Group, Centre for Practice-Changing Research, Ottawa Hospital Research Institute. DM is Associate Professor, Department of Epidemiology and Community Medicine, Faculty of Medicine, University of Ottawa and Senior Scientist, Clinical Epidemiology, Ottawa Hospital Research Institute.