I've been an OR nurse for well over a decade. When I first started in the OR - I found I couldn't 'hear' as well. My preceptor told me that was common in new OR nurses because we are so tuned in to 'hear' with our eyes and the lack of facial expression disrupts our ability to communicate until our brain is rewired. It took a good six months before I noticed I stopped having any issue 'hearing' people speak through their masks. Having said this - OR nurses also know how to communicate a world of expressions with the area between their foreheads & the bridge of their nose. ;)