Maximizing Mouse (Not Keyboard) Potential
sungho.blog
sungho.blog
I'm sure there are trackball prodigies that can do great things with them, but for the masses, they're not optimum.
In their marketing material from the early 90s (the date of your study) Kensington used speed as a key argument. http://xahlee.info/kbd/kensington_expert_mouse_hist.html