Sensory-specific and motivation-specific satiety for the sight and taste of food and water in man.

In normal weight humans it was shown first that the sight of food is pleasant when hungry, and that the pleasantness of the sight of a food which has been eaten to satiety decreases more than the pleasantness of the sight of foods which have not been eaten. Thus the specificity of satiety extends to the visual modality, and this may be an important factor in influencing which foods are selected for ingestion. Second, it was shown that the pleasantness of both the sight and taste of food are modulated in a motivation-specific manner, in that in hungry and thirsty humans the pleasantness of the sight and taste of food but not water is decreased by eating to satiety, and the pleasantness of the sight and taste of water but not food is decreased by drinking water to satiety. Third, it was shown that sensory-specific decreases in the pleasantness of the taste of a particular food produced by its ingestion are associated with only minor changes in the intensity of its taste, which do not account for the changes in pleasantness as shown by an analysis of covariance and by the relation between pleasantness and intensity, so that it is unlikely that sensory adaptation is an important part of the mechanism of sensory-specific satiety.