Establish a Concordance Between the Mismatch Negativity Amplitude and a Score of Logatoms Discrimination, Both Highlighting Capacities of Auditory Discrimination, in Adult Cochlear Implant Users

Context of the study Cochlear implant is an effective and recognized long-term solution for people with severe to profound neurosensory hearing loss. Its principle is to collect sounds of the environment, to analyze them, to transform them and, using an electrodes array placed in the cochlea, to transmit them back to the auditory nerve by electrical impulses. With practice, these are integrated and then recognized by the brain that associates a meaning. For normal hearing persons, speech recognition involves several time and frequency cues that the ear is able to decode. However, the cochlear implant distorts and alters some of these speech cues; the implant easily retransmits the temporal features but the frequency ones are much deteriorated. Thus, cochlear implant users preferentially use the temporal cues, which provide truncated and incomplete information, which often results in a lower quality understanding. Thus, learning or re-learning the language through the cochlear implant is difficult for the young deaf child as for the deaf adults.

The cochlear implant setting is essentially based on perceptual features. A detection threshold and a comfort level are fitting according to the perceptions of the patient and several objective tools. These provide important information but do not on the validity of the setting to ensure optimal speech understanding. The High Authority of Health suggests speech therapy in the overall rehabilitation of cochlear implant users. This aims to develop auditory skills according to four major perceptual axes: detection, identification, discrimination and understanding of sounds.

Despite these cares, cochlear implant users have speech recognition scores lower than those of normal-hearing people and have heterogeneous performances. Deafness etiology (auditory neuropathy, demyelization, ...), integrity of the auditory nerve, position of the electrode array in the cochlea, cognitive abilities, age implantation, duration of hearing loss, quality of cortical integration, cerebral plasticity, speech therapy, the family environment, implant fitting could affect subject performances.

Difficulties in speech understanding may be related to poor discrimination of phonemes, the smallest units of oral language. These phonemic confusions can be tested in adults by several tests such as the Phonetically Balanced Kindergarten test (PBK). However, in the very young child, childs with polyhandicap or the disabled adult, the evaluation of the language is more delicate and needs a long term.

Several electrophysiological techniques would nevertheless make it possible to objectively demonstrate the ability to discriminate phonemes in one measure. For example, the mismatch negativity wave (MMN) reflects a cognitive process showing the discrimination of two different sounds by the auditory system. It is measurable in adults and children, automatically and regardless of the level of vigilance. In this study use a MMN protocol to highlight phonemic discrimination capacities and then link them to subjective performances in the adult cochlear implant users. The first objective is to establish in these users a concordance between the amplitude of the MMN and a test of discrimination of logatoms, both highlighting the capacities of auditory discrimination. The second is to establish a concordance between the amplitude of the MMN and the scores obtained with the PBK.