thumb pick technique

This is a 1.59 minute video response from Jim Deeming on Nov 1st, 2008

Question:

"Greeno asks, "Jim, I've noticed in some of the songs that you play that you use an upstroke with the thumb pick and it gives the riff an additional sense of syncopation. I'm having some problems with that and wonder if you could share any excercises that would improve my ability to do that. Great lessons BTW. Thanks. greeno""