The Nature of Emotion
Modern usage posits emotion as the construct for explaining how an organism reacts to significant events. More than what we think or how we decide, emotion is the central organizing mechanism of response. The most complex form of this construct, human emotion, is generally assumed to have many key components, including physiological arousal, motor expression, action tendencies and subjective feeling. But a fundamental characteristic of all emotional experience is the aspect of pleasantness-unpleasantness.
Recent brain imaging studies have demonstrated that emotion consists of two fundamental activation systems that are separate and independent, and controlled by separate areas of the brain. These two emotional response systems are referred to as positive and negative activation. Positive emotional activation is associated with emotional states such as joy, happiness and pleasure. Negative emotional activation can develop when an obstacle is placed in the way of achieving a goal. One also sees an elevation in negative activation can develop when an obstacle is placed in the way of achieving a goal. One also sees an elevation in negative activation when stress or tension levels increase, such as when someone is viewing a drama. The two activation systems are often reciprocal: e.g., high positive emotion and low negative emotion result in high liking. However; they are not always reciprocal: feelings such as bitter-sweetness or ambivalence illustrate a persons capacity to feel conflicted or mixed toward someone or something.
All forms of emotion are accompanied by expressive and physiological changes that are distinctive and involve both central and autonomic nervous system activity which can be measured.
Emotional Activation and Facial EMG Measurement
Verbal and paper and pencil measures are limited in their ability to assess emotional responses. Respondents may not be able or willing to put into words their complete and accurate emotional response to a stimulus. They are retrospective in that respondents have to think back to remember what they felt, and as well the reporting is susceptible to social demand influences.
Symbols in place of words have also been tried as a method to get beyond the limits of words; but these measures still have an inherent social demand bias and are still retrospective. Dial turning methods have also been tried to assess the moment to moment emotion measurement. However, dial turning is not a natural emotion behavior. It still requires cognitive control and diverts attention from the stimulus.
A better emotions-based measurement approach to self-report is to measure a naturally occurring marker that accompanies changes in emotional state, and doesnt require cognitive effort or memory to produce. Physiologic measures reflecting autonomic nervous system activity like heart rate and skin conductance are incomplete as measures of emotion, as they mostly reflect arousal and only do a limited job at best in indicating emotional valence. The study of the brain with imaging methods such as functional MRI (fMRI) is intriguing and potentially very informative, but currently its not understood which brain activation patterns are desirable, and current theory is too rudimentary to provide direction. At this point fMRI studies are also expensive and time consuming.
One physiological system that has been found to display emotional valence and is a natural emotion marker is the face. Charles Darwin first wrote about the changes in human facial expression as reflecting the individuals current emotional state and to be a means of communicating emotional information. Paul Ekman, the prominent emotion researcher at UC Berkley, and his colleagues have shown that certain configurations of facial muscle movements have been identified with the expression of specific emotions across disparate cultures. In order to measure changes in facial expressions that reflect emotional experience, Ekman and colleagues developed the Facial Action Coding System (FACS), which codes observable facial muscle movements.
Facial Electromyography (or facial EMG) is emerging as a more precise and sensitive method to measure changes in facial expressions than visual observation. Typically EMG measures muscle activity by detecting and amplifying the tiny electrical impulses that are generated by muscle fibers when they contract. Facial EMG measures minute changes in the electrical activity of facial muscles, which reflects minute muscle movements. This technique has been shown to be capable of measuring facial muscle activity to even weakly evocative emotional stimuli. Even when subjects are instructed to inhibit their emotional expression, facial EMG can still register the response.
Facial EMG studies have found that activity of the corrugator muscle, which lowers the eyebrow and is involved in producing frowns, varies inversely with the emotional valence of presented stimuli and reports of mood state. Activity of the zygomatic muscle, which controls smiling, is positively associated with positive emotional stimuli and positive mood state.