The perception of sound by the human auditory system is a complex process and its understanding is of major importance for many applications in our everyday life, e.g., the estimation of noise emissions, or the development of hearing aids. The mechanics of the human auditory system and the perception of sound are investigated in psychoacoustics. Psychoacoustic studies and measures help to characterize the perception of sound. The scope of this thesis is the perception of loudness and sound intensity. Loudness perception, among other aspects, depends on temporal and spectral properties of a sound. In the present thesis temporal and spectral effects of loudness as well as the changing of the perception of loudness and sound intensity in hearing-impaired listeners are investigated. Especially regarding the loudness of subcritical noise bands, the presented results are challenging for current ideas of modeling loudness perception.