When doing vibrato, should I bend the string both up and down or is it fine to just bend it one way? For example, if I want to add vibrato to a note on the g string, should i bend it first toward the d string and then the b string (or vice versa) like in this video http://www.youtube.com/watch?v=VT0y4rIZwhE&feature=relmfu or would it be fine to just bend toward one of them?

This video has got me a bit confused since in most videos that i've seen people seem to just bend the string in one direction even if it's one of the middle strings and there's room on the neck to bend it both ways. Also, if you're supposed to bend in both directions, how do you manage a one and a half step or even just a whole step vibrato?

Thanks in advance.
They sound a little different, it's worth getting the hang of both.

If you're doing a bend and vibrato, generally you go both ways, with the "target" pitch in the middle.

If you bend both ways you can still do a half step, a whole tone gets pretty hard though. Give it a go.