In the newly established video coding standard H.265/High Efficiency Video Coding (HEVC), temporal distortions are introduced under certain coding configurations, which are perceptually annoying at medium and low bitrates. In this paper, two typical temporal distortions due to temporal quality fluctuations in HEVC, i.e., temporal flicker artifact (TFA) and temporal pumping artifact (TPA) are explored in terms of their perception. The coding parameters influencing the perception of TPA and TFA are analysed. The related work in this paper is useful for understanding the fundamental reasons of temporal distortions in HEVC and for HEVC coding to alleviate, or even eliminate the TPA and TFA.