Demant's transfer of its cochlear implant activity to Cochlear. Slow recruitment and misalignment with Cochlear's interests are also determining factors.

This trial is a monocentric, prospective and controlled study of the pupil response to detect hearing threshold and comfortable loudness of normal-hearing (NH) and CI-subjects.

The purpose of the clinical investigation is to explore the pupil dilation response of subjects with a cochlear implant and to provide proof of concept that it is possible to perform the adaptation of a cochlear implant using pupillometry.

The population of this study is divided in 2 group:

• A control group with normal-hearing listeners.
• An Cl group with subjects with bilateral, severe-to-profound sensorineural hearing loss, with at least one cochlear implant for more than 6 months.

Mainly used in audiology to evaluate listening effort, pupillometry is an objective measure that could also be used for fittings. Studies have shown that sound intensity influence pupil dilation. indeed, normal hearing and hearing aids subjects exhibit larger pupil responses with increasing intensity/loudness. The purpose of this study is to explore the pupil dilation response of cochlear implant subjects and to provide a proof of concept that we can perform cochlear implant fitting using pupillometry.

Implanted subjects (Cl group) will undergo up to 3 visits:

1. Visit 1 or V1(inclusion) on day 1,
2. Visit 2 or V2 (Experiment 1-+2+3 or Experiment 1+2 or Experiment 3 )* up to 1 month after V1
3. Visit 3 or V3 (Experiment 1+2 or Experiment 3, optional)* up to 1 month after V2 *lt is up to investigator decision to conduct experiment 1+2 and experiment 3 the same day or in on independent visit (no matter in which order)

Normal-hearing listeners (control group) will undergo up to 2 visits:

1. Visit 1 or Va (inclusion) on day 1,
2. Visit 2 or V2 (experiment) up to 1 month after V1

Inclusion Criteria:

• Both groups:

  • Adult (≥ 18 years old)
  • Fluent in French language
  • Affiliation to social security
  • Information and signature of a written consent prior to any study-specific procedure

• Control group (normal hearing in regards of age):

  • Normal hearing participants according to pure tone hearing levels defined for age and tested frequency (audiometry ISO 7029 and Wand & Puel, 2020 recommendations for hearing loss at the tested frequencies)

• CI group (cochlear implant subjects):

  • Bilateral, severe-to-profound sensorineural hearing loss, with at least one cochlear implant system
  • Using Oticon Medical Neuro Cochlear Implant System (NCIS) or Digisonic Cochlear Implant system (DCIS), unilateral or bilateral
  • Duration of cochlear implant experience ≥ 6 months (period from cochlear implant activation to study enrolment)
  • Pure Tone Audiometry must be strictly below 50 dBA, CI aided.

Exclusion Criteria:

• Both groups, according to the best practices for pupillometry (Winn et al., 2018):

  • Eye diseases: nystagmus, amblyopia, and macular degeneration
  • Severe head injury or any history of significant neurological problems: These issues can affect gaze stability, congruence of eye movements, and pupil dilation
  • Concomitant medication that can impact the parasympathetic autonomic nervous system
  • Person under State Medical Assistance (AME for "Aide medical d'état" in French)
  • Use of one of the following treatments: Trihexyphenidyl, Biperiden or Tropatepine (anticholinergics, commonly used in the treatment of Parkinson's disease)
  • Person under legal protection (guardianship, curators, other, etc.) or under family authorization
  • Unwillingness or inability to comply with all investigational requirements
  • Additional cognitive, medical, or social handicaps that would prevent completion of all study requirements