70% of the world’s languages are tonal and about half the global population speak a tonal language. In the past, research highlighted the limitations of cochlear implant technology in providing the spectral and temporal cues necessary for listeners to perceive and discriminate tones.
However, more recent studies demonstrate that children learning to listen and speak using cochlear implants can develop good tone perception and production. In addition, adults experience improvements in their ability to perceive tones over the first 12 months of implant use.
What Are Tones?
Tones are pitch changes that alter the meaning of words. Tones are described by their pitch height and the contour, which is any change in the pitch height over time. Tonal languages can be defined as either lexical or grammatical, or they can be a combination of both.
Lexical tones distinguish words that would otherwise sound the same. For example, the syllable ‘ma’ in Vietnamese can mean ghost, mother, which, tomb, horse or rice seedling depending on the lexical tone.
Grammatical tones carry information about verb tense, the subject, person and other aspects including negation. Grammatical tones are varied and complex. For example, combinations of high, low, mid and rising tones within one word can indicate past, present progressive or future tense on verbs in some African languages.
How Are Tones Perceived With a Cochlear Implant?
Tones are carried on the fundamental frequency (F0) of the voice. Perception of these low frequencies occurs in people with typical hearing in the apexes of the cochleae.
For cochlear implant users, the selection of a long electrode array that reaches to the apical regions of the cochlear provides a match in both place and pitch for vowel and consonant identification and low frequency stimulation facilitating perception of F0 for tone.
Research has demonstrated that recipients with a long electrode array (31.5 mm) demonstrate better speech recognition than those with a shorter electrode array (24 mm). This was evident immediately following activation and at four years post activation.
Tones in Children With Typical Hearing
Up until the age of six months all infants with typical hearing are able to distinguish tones. This ability diminishes between six and nine months if the child is not exposed to native tonal language speakers.
Discrimination and production of tones with significantly different contours develop early. By 18 months, children learning Mandarin can recognize and produce the difference between tones 1 and 3 and tones 1 and 4.
In contrast, errors in discriminating and producing lexical tones with similar contours (e.g. Mandarin tones 2 and 3) are commonly observed in children between the ages of two and three years.
Facilitating the Development of Tonal Perception and Production
In Children with Cochlear Implants
- Advocate for early implantation with the use of a long electrode array if possible.
- Establish ‘all waking hours’ wear practice for the CI processor(s).
- Immerse the child in a rich spoken language environment to develop a wide vocabulary.
- Adopt a developmental approach for all children initially following implantation.
- Consider music lessons with a focus on melodic pitch training.
- In addition, adopt a remedial Auditory Training approach for children implanted late or those with a hearing age of more than two years who have not developed discrimination of early developing tones.
In Adults with Cochlear Implants
- A focus on rehabilitation in the first year following implantation may maximize the improvement in perception of tones.
- Recommend Fine Structure Processing Strategy.
- Recommend the use of a hearing aid in a non-implanted ear.
- Try Auditory Training to improve discrimination of challenging tone contrasts.
- Utilize strategies to increase awareness of and minimize background noise.
- Practice clarification strategies.
This article was written by Rebecca Claridge, Rehabilitation Manager at MED-EL.
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