A physiological and involuntary response to exposure to a stimulus that starts in the brain and typically affects other mechanisms such as heart rate, facial muscles and perspiration. Emotional response is of high interest to advertisers and marketers because emotion is accepted as being a critical driver of brand perceptions and behavior. It can be measured through human observation (human coding), as well as by EEG, facial coding (see “FACS/ Facial Coding Action System”), and biometrics.