Understanding the way hearing works is important but for the musician wakening up the sense of hearing is even more so. Notice that this is distinct from developing listening skills. This is simply a way to get the sense alive and receptive.
Buy a pair of good quality earplugs and wear them for an hour while going about normal daily business. Be ready for the moment at which they are removed and sound rushes in! This is a simple yet effective way of refreshing the sense of hearing, a bit like fasting for the digestion.
This is a useful exercise to repeat every so often. It also has the effect of focusing attention upon ‘inner’ sounds, as the head and body resonate or produce sounds themselves. At first, the dislocation from the outside world will feel strange, but after a few repetitions of this project it will become natural and easy.