It is important not to confuse arousal level with emotion level. GalvaPhone uses one image to portray two separate pieces of information - the user's self-selected emotion, and the user's current arousal level, as measured by the galvactivator. It is tempting to conclude that the greater one's arousal level is, the more intensely one is experiencing his current emotion. But this is not necessarily the case. For example, if arousal is very high, it could indicate that the user has chosen a misleading face, and is experiencing abnormally high arousal because he is lying about his emotional state.

Along these lines, I thought that the method of animating the faces could be misinterpreted as indicating greater anger, greater sadness, etc. For example, a static angry face might not convey as much anger as an animated angry face in which someone is shaking his fist. The method of keeping the faces constant and static and changing the background color was more of an indication that the basic emotion was the same, and that something else was changing (i.e. arousal).

Thus, in this case, changing color seems to be a better representation of arousal than animated faces, at least in my opinion. But this is ultimately a design decision, and others may have different opinions about this. Perhaps using a combination of animation and color changes would be best to depict both emotional state and arousal level - this is something I could experiment with in the next version of GalvaPhone.