Virginia Anderson’s 2006 article, ‘”Well, It’s a Vertebrate”: Performer Choice in Cardew’s Treatise‘ is viewable on her page on Academia.edu:
http://academia.edu/3551075/Well_Its_a_Vertebrate_Performer_Choice_in_Cardews_Treatise
It’s in draft form and lacks examples from Cardew’s Treatise and other pieces due to copyright issues. But you can see it (and a number of Virginia’s other articles) on these pages, and decide to read these articles in their original settings (this article, for instance, is in the Journal of Musicological Research).