Basically, the Don't Think Twice and such things use a fixed finger picking patern based on double thumbing that lasts about four counts (You could call it two counts, but I have like to count each bass note as a beat)--the high note is a chord note, and acts like a fixed reference--In the Travis picking, the higher notes move around, often with the melody or with ornaments and fills, and, though the bass notes keep pounding away, they can alternate, stay fixed on one note, or walk, depending--Travis picking can have damped bass notes, and often has a much more syncopated or blues/Jazz feel--Nother difference, the first often uses thumb and two fingers, Travis uses only thumb and index, though the index can brush a either up or down--and one may, with practice, do as Jed does, and use the index fingernail like a pick--