## 2 Affective Computing and Emotions
### Emotions Studied in Affective Computing  
Besides the typical popular beliefs which tend to construct some unsophisticated ideas as \"red is stimulating\" and \"blue is tranquil\", as truly mentioned by [PERSON] [24], there is a considerable number of studies which presents empirical results on the topic. Indeed, color is strongly related to emotional states as it will be shown later on. One of the most interesting experiments that proves the hypothesis about the importance of color as a determinant factor in transmitting emotions is [25]. The study consists in carrying out various experiments which show drawings made by psychologically healthy and troubled people, both in chromatic and achromatic condition. The aim is to evaluate the influence of color on the number of right guesses of the participants. Each participant has to indicate which of the two presented pictures has been drawn by a psychologically healthy or unhealthy person. Surprisingly, the number of correct guesses in the case of chromatic drawings is noticeably higher than that of achromatic ones. Another interesting finding is that healthy people use more colors for their drawings than their counterparts. Indeed, psychologically problematic people use a very limited color palette including red, black, and sometimes a few other colors. In addition, emotional changes in people who stay in colored environments is shown. For example, affect change in painted rooms with different orientations to the window has been investigated [26]. The experiment is aimed at discovering potential relations between emotional changes and the following color groups: warm/cool, strong/light chroma, yellow/pinkish/greenish/bluish. Emotional changes in participants are evaluated through the eight primary [PERSON]'s emotions [27]. The author reaches some interesting outcomes, which allow relating color to emotions. In another research, it is shown that staying in rooms painted in bubble-gum pink (Baker-Miller pink) produces a sedation effect [28]. It is also outlined that muscle strength reduces within 2.7 seconds for prison inmates who stay during limited time periods in specially pink painted holding cells. In a study of color-emotion associations by [PERSON] and [PERSON] [29] it is revealed that principal hues comprise the highest number of positive emotions. They are followed by intermediate hues and achromatic colors, which induce the decline of positive emotional response. Based on the obtained responses, the green color attains the highest number of positive emotions, followed by yellow, blue, red and purple. Among the intermediate hues the results of the most preferred include blue-green, red-purple, yellow-red and purple-blue. For achromatic colors the most attractive one is white, followed by black and, finally, gray. Another experiment seeking to evaluate the effects of color images on mental stress reduction is [30]. The participants are shown colored photographs of natural scenery. Each image mainly comprises one of five key colors: pink, green, blue, yellow and red. The same series of images, now in black and white, are prepared for the control group. The color images are presented in the following order: pink, green, blue, yellow, and red. After that, biochemical and emotional parameters (salivary chromogranin-A and salivary cortisol) are measured. A multiple mood scale test demonstrates decrease in depression and fatigue and growth of positive factors such as well-being and intimacy. In addition,, [PERSON] _et al._[31] report about a set of experiments carried out to relate emotional states with colors. The authors put forward the following three hypotheses: emotion-judgment congruence; emotion-target congruence; and emotion-target incongruence. The first hypothesis postulates that people use their current affective state to evaluate a given object. So, people in a happy/sad mood would be inclined to a more positive/negative evaluation of color stimuli (independently of the color tone) than they would if they were in an emotionally neutral state.