PAD Theory
Pleasure, Arousal, Dominance Theory of Emotions
In the 1960's researchers developed the semantic differential technique to measure affective components of total meaning, which, as it turned out, are closely related to the dimensions of affect, feeling or emotion. Three semantic differential factors, Evaluation, Activity, and Potency (E-A-P), emerged and were replicated in diverse experimental settings. Activity, and Potency represented the most rudimentary level of human cognitive response or judgment (i.e., emotion) to any physical or social stimuli and situation. Evaluation, Activity, and Potency, as semantic factors were found to emerge in virtually any situation and across all sense modalities, because these three demensions describe all emotions, and have been shown to be the key intervening variables between any set stimuli and the behavioral outcome.

Evaluation is the high-low evaluation of stimuli (e.g., good-bad, pleasing-annoyed), Activity is the level of arousal assessed from a given stimuli, and Potency is the level of the power created by the stimulus.

Emotion Space
Pleasure-displeasure, arousal-nonarousal, and dominance-submissiveness, are the corresponding emotional reactions to the evaluation, the activity level, and the potency of all stimuli. High-low evaluations of stimuli are associated with feelings of pleasure and displeasure. More active stimuli elicit greater states of arousal and the emotional response arousal-nonarousal is a positive correlate of stimulus activity. Potency elicits either submissiveness, signifying that the emotional response is a negative correlate of stimulus potency or dominance, where the emotional response is a positive correlate of stimulus potency.

Pleasure (P), Arousal (A), and Dominance (D) [PAD] represent the core human emotional reaction system and any emotion can be described as combinations and degrees of these three dimensions. PAD is sufficient to characterize any emotional reaction and the use of all three dimensions is necessary for a complete description of all feelings. Pleasure, Arousal, and Dominance correspond to three nearly independent axes in a three-dimensional model of emotional space. Emotional reactions to any stimuli or situation can be plotted and visually described in this three dimensional space.

The original method used to measure PAD are semantic differential scales based on sets of precalibrated bi-polar emotion denoting adjectives that primarily tap into the intend core dimension. However, researchers have found a number of difficulties with using the verbal based measures. Verbal measures are limited in their ability to separate emotional response from the evaluative processes and do not uncover emotions that are not well vocalized. Verbal measure are cognitively based, which means when responding to these measures subjects are thinking about the emotion and how it relates to the adjectives used. Affective reactions are instantaneous and automatic and because of the cognitive processes involved, reacting to verbal measures distorts the original response to the stimuli in research settings. Moreover, communications conveying emotion are processed using nonverbal channels of communication and require nonverbal measures to fully assess the emotional response. In addition, verbal measures are cumbersome, requiring a large investment in time and resources to analyze a small number of stimuli in a single experimental setting. The solution, in a non-verbal measure, such as SAM.