Layer mask problem

[April H.]

I accidentally hit some unknown button and now my layer mask icon looks different.  It looks like a bullseye and is no longer a black or white rectangle.  The layer mask works as normal but I cannot see where I am painting on the mask.  I just want it to go back to the normal appearance.  I restarted my computer and photoshop with no results.  I am using CS6.  Many thanks! 

[Damien Symonds]

You've just changed your layer thumbnails to "none", is all.

Just right-click on the little brush icon, and choose a larger thumbnail size.

[April H.]

Thanks so much!  Right clicking didn't work for some reason, so I just went to the layers menu, selected panel options, then chose small thumbnail.  You were right, it was on "none".  Thanks again!