Hi Kat,
What a wonderful article to pull up! It certainly does seem that in that instance there is a co-ordination of slow release of the vocalis muscle. Although I have also seen the Thyroarytenoid muscle and the Vocalis muscle labelled as different muscles – each capable of independent movement – in other studies. This might complicate their conclusion!
I can’t claim to be an expert, but Kayes’ and Fisher’s model resonated with me as I have always felt in my own body that there is no gradient between M1 and M2. This is easy to blame on lack of register co-ordination, but I had also never observed a gradient in any of my students or colleagues – some of them seasoned pro’s.
One exceptional student (whose video I will post here but please don’t share widely) bamboozled me when I saw him. When he came to me, he completely lacked any ‘head voice’. But after a year of tuition, he sounded like this. The video is raw, and he wasn’t perfect yet (note the head position and terrible posture!) but the M1 and M2 sometimes sound identical, suggesting a ‘mix voice’.
However, listening now, I can clearly differentiate when he’s in M1 and M2 – but there are certain resonance tricks he’s using to make his M1 sound ‘heady or falsetto-like’. Have a listen, what do you think?
http://mattpocock.com/…/2015/10/Mix-Voice-Guy-Short.mov