Pleasure-displeasure is a feeling state that can be assessed readily with semantic differential measures or with behavioral indicators such as smiles, laughter, and in general, positive versus negative facial expressions. The latter can be reliably scored on a dimension of pleasantness, which is independent of both their aroused and dominant-submissive quality, and thus provide an important behavioral index, particularly in social interaction. Within the present conceptualization, pleasure is distinguished from preference, liking, positive reinforcement, or approach-avoidance. These latter responses have been shown to be affected not only by pleasure, but by arousal and dominance as well. To take one example, Evans and Day (1971) found that looking time at (an approach response to) polygons correlated with their arousing quality but not with pleasure or dominance. The three emotional responses were measured by ratings on semantic differential scales.

Mehrabian & Russell (1974)