If using an image button with a custom background, then the usual touch animation is lost. In order to affect an animation upon touch or click, I created one custom_background.xml that references two backgrounds: a touched background and a default background.
Default background XML in drawable folder (rect_drawable.xml):
Touched background XML in drawable folder (rect_drawable2.xml):
This is the background referenced on each button (custom_back.xml):
The image button's XML would look like this: