hybrid blues finger picking?

ive been watch a few movies and net videos on the blues trying to understand them better. well i have noticed that some blues guitarist playing without a pick using a finger picking style almost like playing the base fingerstyle (thumb index and middle fingers). its not the traditional P.I.M.A. fingerstyle and i wasnt sure what to call it so i called hybrid blues finger style. one of the guitar players that made me really see this clearly was using it while playing a slide solo and looked like he was hitting the a string and the g and b only which sounded great.
does anyone know the real name of this style? or where i can learn it?