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Research - Cued Speech for Enhancing Speech Perception and First Language Development of Children With Cochlear Implants (excerpts)

by Jacqueline Leybaert, PhD Professor of Psychology, Laboratoire Cognition, Langage, et Développement (LCLD), Université Libre de Bruxelles (U.L.B.), Belgium and Carol J. LaSasso, PhD Professor, Department of Hearing, Speech and Language Sciences, Gallaudet University, Washington D.C.

Abstract

Nearly 300 million people worldwide have moderate to profound hearing loss. Hearing impairment, if not adequately managed, has strong socioeconomic and affective impact on individuals.

Cochlear implants have become the most effective vehicle for helping profoundly deaf children and adults to understand spoken language, to be sensitive to environmental sounds, and, to some extent, to listen to music. The auditory information delivered by the cochlear implant remains non-optimal for speech perception because it delivers a spectrally degraded signal and lacks some of the fine temporal acoustic structure.

In this article, we discuss research revealing the multimodal nature of speech perception in normally-hearing individuals, with important inter-subject variability in the weighting of auditory or visual information.  We also discuss how audio-visual training, via Cued Speech, can improve speech perception in cochlear implantees, particularly in noisy contexts.

Cued Speech is a system that makes use of visual information from speechreading combined with hand shapes positioned in different places around the face in order to deliver completely unambiguous information about the syllables and the phonemes of spoken language. We support our view that exposure to Cued Speech before or after the implantation could be important in the aural rehabilitation process of cochlear implantees. We describe five lines of research that are converging to support the view that Cued Speech can enhance speech perception in individuals with cochlear implants.

Concluding Remarks (edited)

Cochlear implants have limitations both in the peripheral signal and in the time course of plasticity. Despite this limitation, the fact that most children can develop language with the cochlear implant suggests that the implant signal does not impose absolute limitations on the development of speech and language. A considerable degree of brain plasticity exists. The incredible capacity of the brain to use the sensory input at its disposal, including multisensory input, can be enhanced further to expand the benefits of cochlear implants for individuals who are deaf. In this process, Cued Speech still plays an important role.

Data collected over the past 30 years have demonstrated that the use of Cued Speech can be a powerful tool for language development and subsequent formal reading achievement by profoundly deaf children without a cochlear implant. Cued Speech enhances speech perception through the visual modality, the acquisition of vocabulary and morphosyntax, and metalinguistic development, as well as the acquisition of reading and spelling (see Leybaert & Alegria, 2003; Leybaert, Colin, & LaSasso, 2010).

The processing of cued information activates in profoundly deaf early cuers some brain areas common with those activated by the processing of spoken language. In an fMRI* experiment on adults who were early cuers (Aparicio, Charlier, Peigneux, & Leybaert, in press), preliminary findings indicate that the identification of words presented in Cued Speech activates the bilateral superior temporal gyrus and the left inferior frontal gyrus in deaf subjects who are early cuers (these areas are also activated by words presented audiovisually in normally hearing participants listening to words delivered auditorily, Hickok & Poeppel, 2000). If confirmed by data with a larger number of cueing participants, these data would indicate that the superior temporal gyrus constitutes an area of processing oral language, regardless of the modality (visual vs. spoken) in which the language is delivered. Further research is needed to establish whether this area also constitutes a site of convergence of auditory, visual (speechreading), and visuomotor (manual cues) information for deaf cuers who are fitted with a cochlear implant.

Prior exposure to Cued Speech, prior to cochlear implantation, also seems to prevent the loss of cerebral plasticity due to late implantation. The fact that children fitted with a cochlear implant, even after 8 years of age, are able to develop oral language abilities (both receptive and expressive) post-implantation, has potential implications regarding the age limit and content of the “critical period” for language development.

The data for the late-implantees in the Kos et al. (2008) study suggest that there is no absolute age limit regarding auditory stimulation: even if auditory stimulation occurs “late”, good results can be obtained provided that the auditory cortices have already been “prepared” to process the information about the phonological contrasts of oral languages.

What seems important is not the fact that deaf children in the Kos et al. study could hear during their first years of life, but that they could get complete, effortless, unambiguous access from an early age to a set of clear, complete phonological contrasts used in their particular language, regardless of the modality (visual vs. auditory) through which these contrasts are delivered. In our view, exposure to a visual language (for example, cued English or another cued language) instigates a process for which infants’ brains are neurally prepared, during which the brain’s networks commit themselves to the basic detection and recognition of phonological patterns in the native language. It is important that this brain activity related to the processing of visual communicative signals or auditory communicative signals occurs early in life. Experiencing a cued language early in a child’s development will have long-lasting effects on the child’s ability to learn that language auditorily later, when they receive the cochlear implant.

Early and intensive use of Cued Speech prior to implantation is likely to become increasingly rare because most children are now fitted with a cochlear implant around the age of 1 year. Audiologists and other related service providers for deaf pediatric populations need to remember that during the first months or years of cochlear implant use, speech perception of an implanted child remains imperfect. Oral comprehension does not develop exclusively by the auditory channel but necessitates audiovisual integration.

A strong case can be made for the addition of Cued Speech to the signal delivered by the cochlear implant in order to help deaf children overcome present limitations of cochlear implants. It is clear that perception of place of articulation, and speech perception in noisy environment can be enhanced by adding the manual cues to the audiovisual message; and, as a consequence, children with a cochlear implant can benefit from Cued Speech experience for the development of precise phonological representations through audition (Descourtieux et al., 1999). These phonological representations can then serve as a platform to launch subsequent development of morphosyntax (Le Normand, 2003; Le Normand et al., in press; Moreno-Torres &Torres-Monreal, 2008, 2010), phonological awareness, phonological short-term memory (Willems & Leybaert, 2009), reading and spelling (see Bouton, Bertoncini, Leuwers, Serniclaes, & Colé, in press; Leybaert, Bravard, Sudre, & Cochard, 2009, for a description of the effect of the combination of Cued Speech and cochlear implants on reading acquisition). 

The author(s) declared no conflicts of interest with respect to the authorship and/or publication of this article.

First printed in: Trends in Amplification 14(2) 96–112  © The Author(s) 2010 Reprints and permission: http://www. sagepub.com/journalsPermissions.nav DOI: 10.1177/1084713810375567 http://tia.sagepub.com 

This research has been re-formatted for ease of reading.

*fMRI, or functional magnetic resonance imaging, looks at blood flow in the brain to detect areas of activity.

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