"Middle" Headlights - how do these work?

Hi folks,

While sorting a burned out HID 'low beam' bulb on my R-Design, I learned that the set of lights in the headlight cluster closest to the radiator grille are not my hi-beams like I always thought. When I pull on the turn signal stalk, the HID (main) headlights go brighter (hi-beams). No combination of switch setting seems to turn these middle bulbs on. How do these work and when do they come on? User manual doesn't address it.