Pulse propagation in the pure-state three-level medium called phaseonium by Marlan Scully is studied both analytically and numerically. Distinctions between SIT-type pulses (e.g., simultons) and EIT-type pulses are most naturally revealed by making use of dark and bright dressed-state amplitudes. We show that EIT-type and SIT-type pulses propagating in phaseonium are to be distinguished by the type of population evolution that they induce.