A few weeks ago I was at choir practice. Our leader was getting us to go back to a song that we hadn’t sung for a while. To encourage us she said (something like), “Don’t worry you’ll remember it. Think of it as being just like muscle memory.” At this point the sopranos were practicing their part so I had the luxury to think, “That’s because it is muscle memory!”
If we get past the subjective experience of listening to and performing a song then singing is just muscle memory; only the muscles are those of the face, throat, chest and lungs. But it is a form of process memory in the same way that the act of carrying out repeated manual tasks become a process memory.
If this is right then it would suggest that singing is controlled in much the same way as manual process memory. Since process memory is less susceptible to the slights of Alzheimer’s Disease then it would help explain why people can sing when they cannot construct sentences.