Layer mask can be hidden or shown using the controls to the left of the layer mask name.

To show or hide a layer mask:

1. In the Layers window, ensure that the Layers display button is set to Paint.
2. All layer masks are shown, by default, when they are created. If you wish to hide a layer mask, click the (-) symbol to the left of the paint layer name. All the layer masks below the paint layer will be hidden, and the symbol next to the paint layer name will change to a (+). Click the (+) symbol to show the layer masks.