I think it has to do with what its blocked with and whether its accepting/producing. I think producing intuition blocked with logic is most likely the standard conception of "mental imagery" which is sort of like a big picture view of many inter related parts hanging together in a logical relationship. that said, I think mental imagery can mean literally anything because all humans are capable of it and for that reason all have something in mind which is real that counts as mental imagery. the best way to get at this is ask the person what they mean when they said mental imagery. I don't think, in the final analysis, its tied to one function like "Ni", I think rather it can be experienced in 16 different ways