What Is Electric Acoustic Stimulation?
Electric acoustic stimulation (EAS), also called electroacoustic stimulation, combines acoustic amplification for low-pitched sounds with cochlear implant stimulation for higher-pitched sounds in the same ear. It may be considered when useful residual low-frequency hearing remains, but hearing aids provide limited speech clarity.
The acoustic component provides hearing-aid amplification for low-pitched sounds so the ear can use its remaining natural hearing. The cochlear implant bypasses damaged inner-ear hair cells and sends electrical signals to the auditory nerve. Your brain learns to interpret these signals alongside the acoustic sound. EAS does not restore normal hearing.
Residual hearing means the natural hearing that remains. Low-frequency hearing can provide information about voice pitch, rhythm and music, while higher frequencies help distinguish consonants such as ‘s’, ‘f’ and ‘t’. Combining acoustic and electric stimulation may support speech understanding in quiet and background noise. Benefits vary between individuals and depend partly on how much usable acoustic hearing remains.
EAS, Hybrid Implants and Bimodal Hearing
EAS combines electric and acoustic stimulation in the same ear. The term ‘hybrid cochlear implant’ often refers to an implant approach intended to support this combined hearing. EAS is not defined by a particular brand or one electrode length.
Bimodal hearing uses a cochlear implant in one ear and a hearing aid in the other. The key distinction is where the two forms of hearing are combined: EAS uses the same ear; bimodal hearing uses opposite ears. Assess each ear’s hearing arrangement separately.
Hearing Difficulties That May Prompt Assessment
Some people with high-frequency hearing loss can hear a voice but cannot make out the words. They may miss consonants, find telephone calls unclear or struggle to follow conversations in restaurants and meetings. This pattern can occur with normal hearing to moderate hearing loss at low frequencies and severe to profound hearing loss at high frequencies.
On a hearing-test chart, or audiogram, this may form a steep downward slope, sometimes called ‘ski-slope hearing loss’. You may hear the rhythm of speech while missing details needed to understand it. These difficulties do not, by themselves, establish whether EAS is suitable.
Appropriately fitted hearing aids remain an important option. However, when inner-ear damage is severe at higher frequencies, making sound louder may not provide enough speech clarity. Hearing-aid adjustments and speech recognition tests help determine whether an implant assessment is appropriate.
When to See an ENT Specialist
Arrange a review if speech remains unclear despite hearing-aid adjustments, or if listening becomes tiring and affects daily conversations. You do not need to have lost all natural hearing before discussing implant options.
Bring your hearing aids, previous hearing-test results and examples of situations you find difficult. These help the team understand whether the main problem is hearing soft sounds, recognising speech or managing background noise.
A sudden drop in hearing needs urgent medical assessment, even if you already use hearing aids. Do not wait for a routine EAS appointment.
Diagnosis
Assessment starts with an ENT review and audiological testing. The audiologist measures auditory thresholds at different pitches in each ear. Low-frequency thresholds help show whether acoustic amplification may be useful. Your preoperative thresholds provide a baseline for checking hearing preservation after cochlear implantation.
Your team should check and optimise hearing aids before aided speech recognition testing. These tests assess how well you recognise words or sentences with your hearing aids, rather than simply how loud sounds must be before you detect them.
Your team also considers your medical history, communication needs and ability to attend follow-up appointments. CT or MRI imaging may be needed to assess the cochlea and auditory nerve. The assessment addresses four questions:
- Does the hearing pattern support consideration of EAS?
- Is the remaining low-frequency hearing usable with amplification?
- How much speech understanding do appropriately fitted hearing aids provide?
- Are the ear anatomy and overall health suitable for cochlear implantation?
Cochlear implant suitability depends on the combined findings. No single speech recognition score applies to every EAS system or patient. Check device indications and local requirements for the proposed treatment.
Surgical Options
Electric acoustic stimulation requires cochlear implantation. The internal receiver is placed beneath the skin behind the ear, and a flexible cochlear implant electrode array is inserted into the cochlea. Hearing-preservation surgical techniques aim to minimise damage to the structures that support remaining natural hearing, but preservation cannot be guaranteed.
Soft surgery aims to preserve residual hearing by gently inserting the electrode array. Insertion through the round window, a natural opening into the cochlea, has been associated with better hearing preservation in some studies, but no approach is best for everyone. Electrode shape, length and flexibility influence how the array fits the cochlea. Flexible designs aim to reduce insertion forces and preserve low-frequency hearing.
Your surgeon may use corticosteroids around cochlear implantation to reduce inflammation. Evidence on their hearing-preservation benefit varies, and treatment depends on your circumstances. Research continues into protective medicines and less traumatic electrode designs.
During assessment for a hybrid cochlear implant, your surgeon reviews residual hearing, ear anatomy and electrode choice. Discuss cochlear implant surgery and costs, including programming and hearing support, before deciding whether to proceed.
