how to move front and back

[nasr]

vizact.whilekeydown(viz.KEY_UP,hand.translate,0,vi zact.elapsed(1),0,viz.RELATIVE_WORLD)
vizact.whilekeydown(viz.KEY_DOWN,hand.translate,0, vizact.elapsed(-1),0,viz.RELATIVE_WORLD)
vizact.whilekeydown(viz.KEY_RIGHT,hand.translate,v izact.elapsed(1),0,0,viz.RELATIVE_WORLD)
vizact.whilekeydown(viz.KEY_LEFT,hand.translate,vi zact.elapsed(-1),0,0,viz.RELATIVE_WORLD)

using the above lines of code i am able to move the marker object up, down, left and right. i want to move it in front and back directions. what are the key attributes for this?