Abstract
Children with sensorineural hearing loss may (re)gain hearing with a cochlear implant—a device that transforms sounds into electric pulses and bypasses the dysfunctioning inner ear by stimulating the auditory nerve directly with an electrode array. Many implanted children master the acquisition of spoken language successfully, yet we still have little knowledge of the actual input they receive with the implant and specifically which language sensitive cues they hear. This would be important however, both for understanding the flexibility of the auditory system when presented with stimuli after a (life-) long phase of deprivation and for planning therapeutic intervention. In rhythmic languages the general stress pattern conveys important information about word boundaries. Infant language acquisition relies on such cues and can be severely hampered when this information is missing, as seen for dyslexic children and children with specific language impairment. Here we ask whether children with a cochlear implant perceive differences in stress patterns during their language acquisition phase and if they do, whether it is present directly following implant stimulation or if and how much time is needed for the auditory system to adapt to the new sensory modality. We performed a longitudinal ERP study, testing in bimonthly intervals the stress pattern perception of 17 young hearing impaired children (age range: 9–50 months; mean: 22 months) during their first 6 months of implant use. An additional session before the implantation served as control baseline. During a session they passively listened to an oddball paradigm featuring the disyllable “baba,” which was stressed either on the first or second syllable (trochaic vs. iambic stress pattern). A group of age-matched normal hearing children participated as controls. Our results show, that within the first 6 months of implant use the implanted children develop a negative mismatch response for iambic but not for trochaic deviants, thus showing the same result as the normal hearing controls. Even congenitally deaf children show the same developing pattern. We therefore conclude (a) that young implanted children have early access to stress pattern information and (b) that they develop ERP responses similar to those of normal hearing children.
Highlights
Language acquisition is a marvelous thing: An infant arrives quite naïve into our world of sound and language and successfully accomplishes the task of attaching meaning to the streams of auditory information that is speech
While there is no definite conclusion on the exact age range optimal for implantation, most studies agree that implantation of prelingually deafened children implanted after the age of about four severely reduces the chance on normal cortical maturation and successful language acquisition with even worse outcomes if implantation occurs after the age of about seven years (e.g., Tyler et al, 1997; Sharma et al, 2007; Szagun, 2010)
A shorter event-related potential (ERP) latency may be expected for the normal hearing children, as they have a longer hearing experience and more mature auditory ERPs
Summary
Language acquisition is a marvelous thing: An infant arrives quite naïve into our world of sound and language and successfully accomplishes the task of attaching meaning to the streams of auditory information that is speech In this process of turning sound into meaningful utterances, one of the most important steps the infant has to master is finding the word boundaries so as to have units to which meaning can be attached (Newman et al, 2006). That the knowledge of boundaries is specific to a particular language becomes obvious when listening to a lengthy utterance in a foreign language, preferably one has never heard before: The listener will have a hard time identifying the words. German phonotactic rules do not allow the segmentation of “lautes Kreischen” (German for “loud screech”) into [laute |skreischen], because/skr/ is not a valid word onset phoneme combination in German, whereas it is perfectly acceptable in English (e.g., “screech” or “screen”)
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