Although HP Reveal does not support AO we would still like to explain what an ambient occlusion map is, as it might be combined in the diffuse map or specular map in order to improve the overall quality of the 3D model.
An Ambient Occlusion (AO) map creates soft shadowing, as if the model was lit without a direct light source, like on a cloudy day.
AO is usually baked from geometry because it is created using a non-realtime ray-casting lighting solution. It can either be stored in a texture.
Typically the AO map is blended into the metalness or specular map, instead of being stored as a unique texture, because this saves memory.
Below is the emissive texture used in the above example.