Fri, 16 May 2025 00:00:00 UTC CU Medicine and the Medical Center at the University of Freiburg in Germany discover precise timing of electrical pulses in cochlear implants helps the brain detect sources of sound Offering hope for restoring the spatial hearing of deaf individuals

The Chinese University of Hong Kong (CUHK)’s Faculty of Medicine (CU Medicine) and the Medical Center at the University of Freiburg, Germany have found that the precise control of the time gap per electrical pulse delivered by cochlear implants (CIs) – the time difference between the sound’s arrival in both ears – can be key to assisting the brain detect subtle timing cues in incoming signals, thereby restoring and improving deaf individual’s capability of identifying the origin of a sound. The findings pave the way for improved cochlear implant designs, bringing new hope to deaf individuals.
The research, co-led by Professor Jan Schnupp from CUHK’s Department of Otorhinolaryngology, Head and Neck Surgery at CU Medicine and Gerald Choa Neuroscience Institute (GCNI), and Dr Nicole Rosskothen-Kuhl from the Department of Otorhinolaryngology in the Medical Center of the University of Freiburg, Germany, has been published in the prestigious international scientific journal Proceedings of the National Academy of Sciences (PNAS).
Lack of temporal precision in CIs may affect deaf people’s spatial hearing
Over one million patients with hearing impairments depend on CIs, which bypass the damaged inner ear hair cells and stimulate the auditory nerve system through electrical pulses. However, CIs still have limitations. Under normal hearing conditions, the brain can distinguish between extremely small time intervals, as low as a few tens of microseconds (millionths of a second, or µs), either between the ears (interaural time differences, ITDs), to tell whether a sound comes from the left or right first, empowering humans with the ability of spatial hearing ability. However, these abilities appear to be greatly reduced in the CI-stimulated brain.
The research team suspected that this is likely due to the fact that current CI devices primarily encode sound information in the amplitude of pulse trains (envelopes), neglecting the precise timing of the electrical stimulus pulses sent by these prosthetic devices. In other words, without precise timing of electric pulses, the electrical pulses stimulate the auditory nerve with mixed signals from both sides, making it difficult to locate from which the sound comes from. To test this hypothesis, the researchers needed to develop an animal model that allowed them to assess the effect of different stimulation strategies in isolation, without the confounding effects introduced into human studies by clinical care standards or patient histories.
They implanted CIs in eight early-deafened rats to indicate whether electrical stimuli delivered to their auditory nerves could be perceived as originating from specific sound sources. The animals quickly learned to lateralise even very small ITDs of 80 µs or smaller with high accuracy, displaying an ITD sensitivity similar to that in rats and humans with normal hearing but much better than that typically seen in human CI users with bilateral implants. The team then designed electrical stimulus patterns to evaluate the impact of ITDs based on the amplitude of a train of pulses and ITDs based on individual pulses. The result of the experiment showed that the animals’ perception depended very strongly on the ITDs of individual pulses and very little on the amplitude-based ITDs. This challenges existing clinical practice of CIs and calls for a redesign of CI stimulation strategies to better align with the auditory system’s natural sensitivity.
Dr Rosskothen-Kuhl said: “The research findings challenge existing clinical applications, which may have overlooked the time differences of auditory input to both ears and failed to time stimulus pulses to auditory nerves with the required precision. This oversight may contribute to the difficulty many CI users experience in localising sound sources. The new animal model allows us to overcome the limitations of existing CIs, while showing that temporal features can easily be resolved down to 80 µs or better when CIs are well designed to capture the rhythm of sound precisely.”
Professor Schnupp added: “This groundbreaking study suggests that the poor spatial hearing and perhaps also the poor pitch discrimination experienced by many CI users, especially those deafened early in life, may stem from the way current devices deliver sound information. By prioritising pulse timing over envelope cues, we are able to unlock the brain’s innate ability to process binaural cues more effectively, benefiting more deaf patients by redesigning CI stimulation strategies.”
The research is funded by CUHK’s GCNI, the Hong Kong General Research Fund, the Hong Kong Health and Medical Research Fund, the Shenzhen Science Technology and Innovation Committee, and the German Academic Exchange Service, with the support of Taube Kinder Lernen Hören e.V. It offers hope for improving binaural hearing in CI users, potentially enhancing their ability to locate sounds and understand speech in noisy environments. The researchers will conduct further studies to explore translational applications in human CIs, such as incorporating precise temporal encoding and improving the design of those CIs, with the vision of creating new-generation bionic ears.

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