how to define an object (button) that has a text value associated with it

Similar thread:

http://community.smartbear.com/t5/Getting-Started-with/Map-object/m-p/88790#M17264

If there's no caption you can switch on Text Recognition for the project. Then you should be able to spy the button text. 

Using the Calculator as an example, the number buttons are "WndClass: Button", so:

Right Click on Project folder > Edit > Properties
Open Applications > Text Recognition > add the "Button" class.

Now when you spy the calculator buttons the text will also be highlighted so can be mapped.

Link for the Text recognition overview

http://support.smartbear.com/viewarticle/56486/