Mary, if you have ten minutes to spare you may find this video of experiments on plants' response to sound interesting (Mythbusters). I would have said a response to the carbon dioxide that you breath on them would be the most likely beneficial effect but it seems they respond to noise as well. The two videos need to be watched in sequence, part 1 and part 2.
I would think gently touching them could also be beneficial, some people run a small fan on seedlings to make them more sturdy (also to reduce damping off by increasing air circulation. Anyway, these are the videos:
https://m.youtube.com/watch?v=...
https://m.youtube.com/watch?v=...
