Major challenges are:

• Acoustic Scene Analysis. Microphone configurations (on the hearing aid, on both hearing aids, wearable, hand-held, on table, distributed on other people, within the room) to choose?  Wireless transmission of audio (Bluetooth vs specialized, latency constraints, bandwidth, jamming). Algorithms (beamforming, ad-hoc distributed arrays). How to deal with the diversity of potential solutions within a project like COCOHA (risk of dispersion)? How can COCOHA benefit from/contribute to ongoing work in this field? What solutions might end up in a hearing aid?
• Measuring signals from the brain. Electrode configurations (scalp, circumaural, within-ear). Electrode-skin interface (dry electrodes, active electrodes, high-density electrode pads). Portability. Alternative or complementary measurement modalities (NIRS, high-temperature MEG).
• Processing and decoding of audio and signals from the brain. Audio processing and feature extraction. EEG artifact rejection and denoising.  EEG feature extraction. Joint decoding of audio and EEG. Combining with additional measures (eye-tracker, muscle, gyroscope/accelerometer). What can brain-compute BCI teach us?
• Understanding auditory attention, and its measurable correlates. How do subjects deal with complex scenes? What parameters determine the limits of attention? What are the measurable brain correlates of attention to a source, to a position? How to maximize them?
• Auditory attention and measurable brain signals in hearing impaired. How does impairment affect auditory attention?  How does it affect our ability to measure correlates of attention?
• The wider picture: synergies with other forms of control. Eye-tracking (direction of gaze, microsaccades, pupillometry, EEG correlates of eye movements). Muscular activity (EMG), head and body posture and movements. Graphic and tactile interfaces. User-dependent strategies and learning.
• Integration within a hearing aid. Which of many possible solutions could lead to a viable product? Miniaturization. Power consumption. Cost. Packaging. Marketing. Regulatory and ethical aspects (e.g. privacy). Intellectual property.

COCOHA addresses only a small subset of these issues. Nonetheless, it is important to keep in mind this wider picture: what else remains to be done, what other pathways to explore.  We need to be aware of the alternative approaches, how we can benefit from them, and be of benefit to them.