When you look at the thumbnail on the Layers palette in Photoshop you see a small preview of what appears on each layer. If you find that the thumbnails on the Layers palette are too small (or possibly too big) you can change the thumbnail size. Click on the Layers palette menu (the triangle in the upper right corner) and choose Palette Options.
The Layers Palette Options dialog box opens and you can choose from Small, Medium, Large or No thumbnails. Choose whichever option suits you best. I generally use the Large thumbnails if I only have a few layers to deal with because it gives me a better preview of what’s on the layer. If you have a LOT of layers you might want to use the Small or No Thumnails option so that you don’t have to do a lot of scrolling through your layers.