1. A system comprising: an analyzer to analyze brain wave data gathered from a viewer exposed to a media instance to determine a first energy of a first frequency band at a first time, a second energy of a second frequency band at the first time, a third energy of the first frequency band at a second time and a fourth energy of the second frequency band at the second time; a calculator to calculate a first difference between the first energy and the second energy and to calculate a second difference between the third energy and the fourth energy; a processor to: generate a first output signal based on the first difference, the first output signal representative of a first emotional state of the viewer, generate a second output signal based on the second difference, the second output signal representative of a second emotional state of the viewer, and generate a third output signal indicative of a success or a failure of the media instance, wherein a positive change between the first emotional state and the second emotional state are indicative of a successful media instance.