Freudian defense mechanisms, especially repression and projection, have often been the subject of empirical psychological research. The phenomenon of perceptual defense can be viewed as an experimental analogy for repression. This volume offers an overview of empirical studies on unconscious experiences and their effects on conscious experience and behavior as well as on some defense mechanisms. Methodologically, tachohistoscopic investigations on the defense against perception, investigations on the different speed of perception of emotional and semantic aspects, interference investigations and experiments with subliminal psychodynamic activation are taken into account. It turns out that the psychoanalytic concepts examined are empirically supported.