In response to player feedback over object highlighting in Human Revolution, director Jean-Francois Dugas and David Anfossi released a short video explaining how this feature is now optional. During a short demonstration of this, they also revealed some details about difficulty levels. Namely, they will have certain features (such as highlighting) enabled or disabled by default, which can be toggled at any point in mid-game.
Incidentally, the name of the hard setting was “Give me Deus Ex.” Take from that what you will. The video in full is but a short YouTube away.