Select the map u want displayed in the material editor and click the checkered box,if u are using the slate material editor.
In compact mode, navigate to your map, and press the checkered box.The texture will display in your viewport.
If u select the material in either mode, clicking the checkered box will not display the material as corona doesn't support it.
Btw, I wanted to ask- Does Corona material support display of bump map/normal map in viewport as surface relief like other viewport shaders.