A team of engineers and clinicians have used 3D printing to create intricate replicas of human cochleae and combined it with machine learning to advance clinical predictions of ‘current spread’ inside the ear for cochlear implant (CI) patients. ‘Current spread’ or electrical stimulus spread, as it is also known, affects CI performance and leads to 'blurred' hearing for users, but no adequate testing models have existed for replicating the problem in human cochleae – until now.