Auditory Abilities and Language Acquisition in Cochlear Implant Users with Bimodal Stimulation

Abstract

People with normal hearing typically listen with both ears. This enables sounds to be heard regardless from which direction they come, and provides two inputs to the binaural auditory system so that it can selectively attend to the ear receiving the clearer signal. The system can also partially reduce the negative impact of noise on speech intelligibility by combining inputs from both ears (Dillon, 2001).

Binaural hearing is a fundamental property of the normal auditory system. Many individuals with hearing loss in one or both ears have difficulty with this situation. Evidence for binaural benefits when both ears are stimulated compared with stimulation of one ear alone is well documented in normal listeners (Durlach, 1978).

Hearing impairment refers to a condition in which the subject is unable to detect or distinguish the range of sounds normally available to the human ear (Justice, 2006). The incidence of permanent hearing loss in children ranges from 1.2 to 6 per 1,000 live births worldwide. (Olusanya et al., 2006). The early hearing detection and intervention program found 5 to 6 infants per 1000 children as born with hearing loss. Estimates from research in the last 2 decades suggested that about 8% of school children have hearing loss that is educationally significant. This term refers to a hearing loss that is serious enough to impact a child’s ability to perform well educationally (American-Speech-Hearing Association [ASHA], 2005). The prevalence of hearing loss in Egypt is about 16% (Abdel-hamid et al., 2007).

Recognition and management of hearing loss is imperative. Untreated hearing loss in a child has a significant impact on their auditory brain development that results in serious consequences for speech, language, literacy, academic achievements, and social emotional development for the child's life term. These chronic disabilities also impact significantly on the family and community (Olusanya et al., 2006). Children with hearing impairment are at risk of language delay due to receiving insufficient auditory information during the critical period (Nicholas and Geers, 2007). Perkell et al., 2000, stated that there is a well-documented relationship between the severity of hearing loss and intelligibility of speech.

Intervention of hearing impaired children aims at developing healthy, socially and emotionally balanced individuals who are able to integrate into the society and become more generally productive in their societies. (Scheetz, 2001).

Hearing aids and cochlear implants are the two ways to enhance one’s hearing abilities. Hearing aids are small electronic devices inside the ear. They are placed in the entrance to the ear in the external auditory meatus. They are typically molded to fit each individual ear and amplify sound as it is delivered to the ear canal (Roseberry- McKibbin & Hedge, 2011). A cochlear implant is a hearing prosthesis designed to restore or provide a level of auditory sensation to adults and children who have severe to profound sensory-neural hearing impairment and who get limited benefit from hearing aids (Waltzmann, 2006).

Children who receive an implant early in life, followed by a period of appropriate rehabilitation, achieve language and speech skills that exceed levels observed in profoundly deaf children with hearing aids (Geers, 2004). Children who receive CIs at a young age (i.e., under 24months of age) can be expected to achieve some language skills at a rate comparable to hearing age-mates (Svirsky et al, 2004 & Nicholas &Geers, 2007). These children are entering mainstream classrooms in the early primary grades (Geers & Brenner, 2003).