We study the optical properties of a four-level N-type system theoretically for $$^{87}$$ 87 Rb atoms using density matrix formalism. Electromagnetically induced transparency and electromagnetically induced absorption (EIA) are two extensively studied two-photon coherence phenomena. EIA can be observed as a result of the transfer of coherence and transfer of population between the atomic levels. A narrow absorption is observed at the resonance frequency for moving atoms. Enhanced transmission and absorption lead to sub-luminal and super-luminal light propagation, respectively. It is observed that the third field in N-type system causes switching from transmission to absorption. We also discuss group index changes with coupling field strength.