Teaching the dog how to sit and down

[htsource]

My dog knows how to sit and down, but I believe she's looking for my hand rather than my voice. Basically now when I say "sit", she'd just looking at me, then if she sees my hand is holding up, then she'd sit. Similarily if I put my hand on the ground, she'd lie down.

One thing she knows for sure is I won't do anything to her until she's sitting down so she knows if I don't respond to her, she'd eventually sit down and look at me.

Just wondering if I can train her to listen rather than seeing my hand for commands?

Thanks for your help.