lesson 3-08: vibrato 2
'Vertical' vibrato involves 'wobbling' the tip of the fretting hand finger to move the note in and out of pitch. Always be sure to let the string come back to it's starting position, otherwise you will finish the phrase on an out of tune note.
Experiment with subtle vibrato and wide vibrato for more extreme effects. This technique generally sounds better if you move your fretting hand up and down in time with the music. It can be used to good effect when used in conjunction with a string bend in blues or rock music.