"Ps PSD" icons in Adobe bridge

For some reason I don't understand, some files in Adobe Br appear as blue, white and black "Ps PSD" icons instead of image thumbnails.  What's the meaning of these "Ps PSD" icons?  Why would this be occuring?  Why don't these files appear as image thumbnails?  Is there a way to make them appear as thumbnails?  (The "Ps PSD" icons open as images in Ps and can be edited normally, but I can't apply Enhance-SR to them in Camera Raw.)  Thanks