This article from io9 explains a recent study in which people listened to background noise ("an orderly set of new sounds that were somewhere between a tenor saxophone and a French horn") while playing with Etch-a-Sketches, for seven minutes. They were then asked to identify which of three sounds were different. If the sounds didn't fit the expected pattern, the subjects could not figure it out.
I think this is very interesting. So often people think of hearing as being in the ears - but most of our hearing is done in our brains using feedback from our ears.
The study can be found here.