Basic newbie question

I’m a newbie. I admit it. I thought I was getting

Despite my searching, I seem to have lost the ‘live update’ ability when mapping UVs.
When I render, the UVs are all appropriately lined up and my model looks fine, but that’s the only way I can see what I’ve done in the main 3D window! I’m sure I was able to see the effect that altering UVs had live at some point in the past. Any clues as to what I’ve done wrong?

Thanks in advance!

Click the little Lock icon in the UV Editor’s header.