There are many studies in VR and immersive contexts.
Check the (Association of Computing Machines) ACM's VR group for associated info, name, conferences, and journals.
Probably the first line of work on immersion in the natural world (not a made-up VR) is Steve Mann. You can read his pubs, and pubs about him, here.
"Hands-free" Buttons
Re-reading the comments more (you really should update the question) I see that you're concerned with UX and ergo for interfacing apps / functions.
Keep in mind that 'ergo' in the broader context could mean situational usage (e.g. should your surrounding environment impact what data / UX is presented via glass / headset)
I suggest you look into audio interfaces, generally, until you can refine your question further.
Happy hunting, and feel free to ask more questions (so this one doesn't become a 'forum') and @mention me in a comment.