Board Thread:Series general discussion/@comment-5088097-20170624223327/@comment-18014300-20170624232338

I actually don't recall AC1 ever establishing explicitly that Eagle Vision was only the Animus's way of representing the Assassin's observational skills. After all, at the end of the game, Desmond uses Eagle Vision outside of the Animus, and from Assassin's Creed II onward, it's firmly established as part of the lore that it's not an Animus feature. Otherwise Desmond could not have been able to unlock the door to escape the Abstergo facility for instance.

In any case, Eagle Vision is explained in the lore as being a manifestation of the sixth sense of knowledge that the Isu supposedly possessed. I believe that the way it seems to work is that it feeds back answers to questions that the user is mentally processing. So if a user is seeking to distinguish ally from foe, Eagle Vision provides that intuitive "knowledge" for instance. If a user is seeking a passcode for a door, Eagle Vision provides that knowledge.