The image window shows all visible layers in the image. To view a thumbnail of a layer’s contents, hold the cursor over the layer name in the Layers palette.
To turn off or on the visibility of layers in the image window, see Showing and Hiding Layers, Groups, and Vector Objects.
To view the contents of one layer:
On the Layers palette, move the cursor over a layer name to display a thumbnail of the layer contents.
To modify the size of the thumbnail:
Choose File > Preferences > General Program Preferences.
Click the Display and Caching tab.
Set the Thumbnail / Preview setting to the desired size.
Deleting Layers or their Contents
Expanding and Contracting Layers and Layer Groups