How Combined Electrical and Acoustical Processing is Revolutionizing Hearing
Imagine listening to a symphony orchestra where you can only hear the percussion section—the deep thrum of the bass drum and the crash of cymbals, but no violins, no woodwinds, no richness of harmony.
For decades, this was the reality for many cochlear implant users: access to sound, but without the full spectrum that makes listening beautiful and effortless. Today, a revolutionary approach is changing this reality, creating a more natural hearing experience by combining two different technologies to create what many call "the best of both worlds" in auditory restoration 1 .
This breakthrough approach, known as combined electrical and acoustical speech processing or electric-acoustic stimulation (EAS), represents one of the most significant advances in hearing restoration in recent years 1 .
By marrying the precise electrical stimulation of cochlear implants with amplified acoustic sound from hearing aids, EAS creates a synergistic hearing experience that surpasses what either technology can deliver alone. For the millions worldwide with hearing loss—estimated at over 430 million people with moderate or greater hearing loss—this integration opens new possibilities for conversation in noisy environments, appreciation of music, and reconnection with the subtle sounds that give life its richness 4 .
Work by bypassing damaged hair cells in the inner ear and directly stimulating the auditory nerve with electrical pulses. They excel at providing access to mid and high-frequency sounds—exactly the range where most speech information resides. However, they struggle with conveying fine pitch variations and the rich tonal qualities that make music beautiful and voices distinct 7 .
Work by amplifying acoustic sounds. For people with residual low-frequency hearing, hearing aids can preserve the natural quality of sound in these ranges, providing access to the fundamental pitch of voices and the resonant bass notes in music. But as hearing loss becomes more severe, especially in the high frequencies, hearing aids alone often cannot provide sufficient clarity for understanding speech.
Electric-acoustic stimulation brings these two technologies together, creating a complementary system where each technology does what it does best. The cochlear implant handles the mid and high-frequency sounds, delivering clear speech information, while the acoustic component—either through a hearing aid or integrated acoustic amplifier—preserves the natural low-frequency sounds that electrical stimulation struggles to convey effectively 9 .
| Feature | Traditional Cochlear Implant | Combined EAS System |
|---|---|---|
| Low-frequency sounds | Electrical stimulation only, poor pitch perception | Natural acoustic hearing preserved |
| Speech clarity | Good in quiet environments | Enhanced, especially in noise |
| Music appreciation | Limited | Significantly improved |
| Sound quality | Often described as "mechanical" or "robotic" | More natural and rich |
| Ideal candidate | Profound hearing loss across all frequencies | Partial hearing loss with preserved low-frequency hearing |
A fascinating 2025 study published in the journal NeuroImage: Clinical provides unprecedented insight into what makes combined hearing so effective 7 .
The research team worked with 20 unique participants who had single-sided deafness—normal hearing in one ear and a cochlear implant in the other. This population offered a perfect natural experiment: the same person could experience acoustic hearing through their normal-hearing ear and electric hearing through their implanted ear, eliminating the variables that typically complicate comparisons between different people.
The researchers used two advanced brain imaging techniques simultaneously: electroencephalography (EEG) to measure electrical activity in the brain with millisecond precision, and functional near-infrared spectroscopy (fNIRS) to track blood flow changes in specific brain regions, indicating areas of heightened neural activity.
Comparison of brain responses to acoustic vs. electric hearing
The findings revealed fascinating differences in how our brains process these two types of hearing:
The auditory cortex showed smaller and delayed responses when processing sound through the cochlear implant compared to acoustic hearing, particularly for the P2 event-related potential component known to be involved in voice pitch processing 7 .
When listening through the cochlear implant, variable pitch sequences triggered additional activity in the posterior right auditory cortex—a response not seen when the same sounds were presented to the normal-hearing ear.
Despite the generally reduced response, the cochlear implant provided enough acoustic detail for the brain to distinguish between different pitch patterns in speech.
These findings demonstrate that combined hearing systems work not because electric hearing perfectly mimics natural hearing, but because our brains can adapt and compensate when given multiple sources of information. The additional activation in specific brain regions for electric hearing suggests our neural pathways can develop specialized processing strategies when dealing with the different quality of information provided by cochlear implants.
| Brain Response Measure | Acoustic Hearing | Electric Hearing | Interpretation |
|---|---|---|---|
| Response strength | Stronger cortical activation | Weaker cortical activation | More neural resources required for acoustic hearing |
| Processing speed | Faster responses | Delayed responses, especially P2 component | Electric hearing requires more processing time |
| Pitch variation processing | Similar activation for repetitive and variable pitch | Additional right posterior activation for variable pitch | Specialized processing develops for electric hearing |
| Speech distinction capability | Excellent | Sufficient for distinguishing pitch patterns in speech | Cochlear implants provide adequate detail for daily communication |
Advancing our understanding of combined hearing requires specialized tools and technologies. Here are some of the key components driving research and clinical applications in this field:
Designed to preserve residual hearing during insertion. Enables EAS by protecting delicate low-frequency hair cells 4 .
Integrate cochlear implant stimulation with acoustic amplification. Allows seamless combination of both technologies in a single device 8 .
Measures electrical brain activity with millisecond precision. Tracks how quickly the brain processes sounds through different hearing modalities 7 .
Maps blood flow changes in the brain during hearing. Identifies specific brain regions activated by electric vs. acoustic hearing 7 .
Provides modifiable code for testing new sound processing algorithms. Allows researchers to bypass limitations of commercial systems .
Enables real-world testing of sound processing algorithms. Facilitates research in natural listening environments rather than just laboratories .
Once limited to those with profound hearing loss across all frequencies, cochlear implantation now benefits individuals with a much wider range of hearing profiles. Recent guidelines have shifted from strict audiometric criteria to a more patient-centered approach that considers real-world communication challenges 5 .
The recently launched Cochlear™ Nucleus® Nexa™ System represents the next step in this evolution, featuring upgradeable implant firmware—an industry first that allows recipients to access future innovations through updates rather than additional surgery 2 .
Open-source platforms like CCi-MOBILE and Open Master Hearing Aid (openMHA) are democratizing hearing research by allowing scientists to bypass proprietary limitations of commercial systems .
Researchers are exploring fully implantable systems that would eliminate external components, addressing cosmetic concerns and practical issues like water vulnerability 6 . The integration of artificial intelligence promises devices that automatically adapt to individual preferences and acoustic environments, while gene therapy research may eventually complement cochlear implants by preserving or restoring natural hearing structures 6 .
The development of combined electrical and acoustical speech processing represents more than just a technical achievement—it signifies a fundamental shift in how we approach hearing restoration.
Rather than viewing hearing aids and cochlear implants as competing solutions, researchers and clinicians now recognize the profound benefits of integrating these technologies to create a hearing experience that honors the complexity of human auditory perception.
For the millions living with hearing loss, these advances bring new hope for reconnection—to conversations in crowded rooms, to the nuances of music, and to the simple joy of hearing the world in its full richness.
As research continues to refine these technologies and expand access, we move closer to a future where hearing loss no longer means missing life's important moments, but rather experiencing them through a sophisticated blend of nature and innovation that makes every note count.
The journey of hearing technology continues, and it's sounding better than ever.