Evaluation of the CochSyn Test Prototype to Measure Cochlear Synaptopathy

This study investigates a newly developed test, The CochSyn test that can quantify cochlear synaptopathy (CS) (a new type of sensorineural hearing loss (SNHL)) earlier than the current golden standard pure-tone audiogram.This newly developed test is based on auditory evoked brain potentials. A hardware prototype (the Cochsyn test prototype) was developed to use the Cochsyn test in clinical practice. Additionally a CS-based sound-processing algorithm (CoNNear) that is designed to improve speech intelligibility in subjects that are identified to have CS, will be investigated in this study.

Cochlear synaptopathy is a new type of sensorineural hearing loss (SNHL) and is related to ageing, noise exposure and ototoxicity. There is currently no diagnostic test of CS on the market, whereas CS is an important form of SNHL. CS occurs before the golden standard clinical hearing test (pure- tone audiogram in which participants raise their hand when hearing tones of different frequencies and the threshold of hearing is determined), shows any signs of hearing damage.

The investigators have developed a test, the CochSyn test that may quantify SNHL earlier than the audiogram. The newly developed test is based on auditory evoked potentials. This is a method in which an auditory stimulus is presented, and encephalogram (EEG) electrodes capture the sound-evoked brain potentials. The most popular auditory evoked potential metric to diagnose sensorineural hearing loss (SNHL) is the auditory brainstem response (ABR). The first animal research studies on CS confirmed that the ABR wave-I amplitude is a sensitive marker of CS when the inflicted hearing damage is well-controlled and specific. Even though it can be assumed that the ABR wave-I amplitude will also be sensitive to CS in humans, it may not be a differential marker for it, and hence other candidate auditory evoked potential markers for CS have been investigated in recent studies. In particular, the envelope-following-response (EFR), has also been shown to be specific to CS in animal research studies.

EFRs are recorded using the standard ABR electrode montage but use another type of stimulus. Based on model simulations and a recent study in which the investigators compared candidate EFR markers for use in human studies , the investigators have developed a new stimulus for EFRs that uses both a different type of modulator waveform and a different analysis method than was adopted earlier.

In this trial, the investigators wish to test the performance of the new method (the CochSyn test) in listeners with or without self-reported hearing difficulties using a newly developed hardware prototype (the CochSyn test prototype), dedicated for the CochSyn-test in clinical practice. The assessment also includes the testing of a CS-based sound-processing algorithm (CoNNear) that is designed to improve speech intelligibility in subjects that are identified to have CS, based on our CochSyn test.

To this end, the investigators will first assess whether our CochSyn test prototype is equally good at capturing the standard ABR waveform as a comparator device available on the market (the Intelligent Hearing Systems Universal Smart Box). The investigators will also test which stimulation characteristics and electrode configurations for the CochSyn test are best able to quantify individual differences in standard objective hearing tests (audiogram, otoacoustic emission, speech reception thresholds) and subjective hearing complaints (validated HHIE-s questionnaire).

Eligibility Criteria:
Inclusion Criteria:

Session 1

Test group

* 18 - 87 years old
* Flemish/Dutch as native language
* Ability to fill out a questionnaire and to perform a speech intelligibility test
* Self-reported hearing difficulties according to HHIE-s questionnaire (score of \>4)
* Normal audiogram (for age group 18-77): audiometric thresholds up to 4 kHz ≤ 20 dB HL and for 6 kHz ≤ 40 dB HL in at least 1 ear OR impaired audiogram (for age group 18-87): audiometric thresholds between 20.1 and 64.9 dB HL pure tone average at 0.5, 1, 2, and 4 kHz in at least 1 ear (=Mild to moderately severe hearing loss according to the recommendation by the Global Burden of Disease Expert Group on Hearing Loss)

Control group

* 18 - 77 years old
* Flemish/Dutch as native language
* Ability to fill out a questionnaire and to perform a speech intelligibility test
* No self-reported hearing difficulties according to HHIE-s questionnaire (score of ≤4)
* Normal audiogram: audiometric thresholds up to 4 kHz ≤ 20 dB HL and for 6 kHz ≤ 40 dB HL in at least 1 ear

Session 2

* Participation in session 1 in the test group
* 18 - 77 years old
* EFR magnitude at 4 kHz with Snap electrode in session 1 reduced by 30-100% compared to average EFR magnitude of age group 18-27 of control group (session 1)

Exclusion Criteria:

Applicable for both sessions:

* Pregnant woman
* Breastfeeding woman

Applicable for both sessions and the ear which fulfils the inclusion criteria:

* Chronic (longer than 6 months) permanent tinnitus
* Hearing loss due to a genetic condition, a middle ear condition, or surgery
* Congenital hearing loss
* Blocked ear canal