The ACTION project builds on the recent discovery that relatively low levels of pulsed infrared laser light are capable of triggering activity in hair cells of the partially hearing (hearing impaired) cochlea and vestibule. So far the excessively large volume of optical fibre systems and external light sources used for animal studies prevented the practical use of this discovery for long term animal research devices or for human grade implants. ACTION aims to develop a self-contained, smart, highly miniaturised system to provide optoacoustic stimuli directly from the electrode array of a cochlear implant system. The resultant neural cell response will be electrically recorded and direct feedback to the light source will be provided to enable automated, objective hearing threshold assessment and optimization of sound feature coding enhancements for improved quality of the acoustic sound. The new implant is aimed to lead to more effective non-contact treatment, as a device with intra-cochlear sound sources offers many potential advantages over a traditional in the ear hearing aid/speech processor combination. This approach will at the same time avoid damage of neural tissue by high electrical current, and introduction of high-frequency artifacts to the recording signal. Biocompatible, long-term implantable materials for micropackage and integration principles for the light sources (specific pulsed vertical cavity surface emitting lasers optimized for optical neurostimulation) will be selected. The project includes neural response measurements and communication between discrete elements to achieve robust and reliable miniature standalone devices with high acceptance within the medical sector. Pre-clinical tests for optoacoustic cochlear implants will be an integral part of the project.