Sorry for a vague explanation, i think by showing a sample will explain it more detailed,
http://www.youtube.com/watch?v=QjA5faZF1A8
0:20 - 1:20 what im after is the wrist movement .
Or even this
http://www.youtube.com/watch?v=90i73...eature=related
0:40 - 0:42 the way irojiro pick those strings with only wrist movement.
2:13 - 2:30 how he strum with only wrist movement.
Hope you get what i meant