This video explains it nicely starting at about 1:20 in.
Also see here.
This is a pretty interesting article on flying it as well. It really seems to depend on mode but its summarized here nicely,
Climbing into the front seats of the Osprey definitely does not
produce the most graceful entrance: it requires some contorting around
the armrest, center console and overhead panel. The cockpit is
dominated by four night-vision-goggle-compatible, six-inch-square
multi-function displays that allow access to flight, navigation and
system information. Mechanical flight controls consist of a center
control stick, thrust control lever (TCL) and rudder pedals. The
control stick functions as cyclic control while in conversion and
helicopter modes, but steadily fades into a traditional airplane
control stick as the nacelles transition to airplane mode.
moves fore and aft just like an airplane throttle, unlike a helicopter
collective. It does operate as a collective control, however, and
becomes a traditional throttle during the transition. While this may
seem counter-intuitive to helicopter pilots, it actually makes a lot
of sense, because regardless of the mode of flight, youre always doing
the same thing: controlling the thrust vector. Forward on the TCL in
helicopter mode is the same as raising the collective in a helicopter,
and vice versa. The first couple of hours for helicopter pilots
transitioning to the Osprey highlight a bit of collective dyslexia,
but very quickly it never becomes a further problem. A spring-loaded,
knurled rotary knob on the TCL that lies in contact with the pilots
left thumb controls the nacelles. Roll the thumbwheel aft and the
nacelles rotate to the vertical, roll it forward and the nacelles
continue to the downstops. The controls follow the hands on throttle
and stick, or HOTAS, concept, and have all the controls necessary on
them to control multiple systems on the airplane.