A user's experience of a product involves a set of state transitions. For example, the state of a sensory modality may shift from vision to touch to perceive a quality of a product. Between such state transitions, users expect experiences of the subsequent states as well as experience the current state event. A discrepancy between prior expectation and posterior experience evokes emotions, such as surprise, satisfaction, and disappointment, affecting the perceived product value. A noteworthy psychological phenomenon is that expectation affects perceived experience. This phenomenon, called the expectation effect, is a key to designing the affective experience of a product. Although experimental findings of this effect exist in a variety of disciplines, general and theoretical models of the effect are largely unexplored. In this paper, we propose a theoretical model of the expectation effect using information theory and affective expectation model. We hypothesize that Shannon's entropy of prior subjective probability distributions of posterior experience determines the occurrence of an expectation effect, and the amount of information gained after experiencing a posterior event positively relates to the intensity of the expectation effect. Furthermore, we hypothesize that the conscious awareness of expectation discrepancy discriminates the two types of expectation effect, assimilation and contrast. To verify these hypotheses, we conducted an experiment using the tactile quality of surface texture. In the experiment, we extracted the visual expectation effect on tactile roughness and analyzed the causes of the effect based on these hypotheses. The experimental results validated the proposed model.