If your PSD file contains an alpha channel,
you must follow these steps in order to display the alpha in Maya
(for example, the scene view, the interactive renderer and the renders).
Under
the PSD file node, by default, the attribute Alpha
In Use is set to Default.
By default, this ignores the alpha channel.
Select
your alpha channel under the Alpha In Use drop-down
list instead. You should now be able to view your alpha in the scene
view.