[roesel]

In my opinion, this question is impossible to properly answer in the framework of Maxwell's equations / field representation, since it cannot be defined in those terms.

If I were to answer this question in terms of photons as small amounts of field oscillations, I would argue that these are "new" photons, due to the fact that the "old" ones induced oscillations in the dipole moment of the material, which then in turn radiated energy out as the "new" photons.

But you can just as easily think of it as the material "suggesting" a better direction to the field propagating through it, and thus reorienting it. This is just very difficult to imagine and describe, at least for me.