A core premise of the cascade theory involves conflict, long considered to have only a negative impact on a marriage. In the laboratory, couple interactions are studied intensively over about 20 hours, including a session during which the couple is videotaped discussing an issue that is creating tension between them. Physiological readings are taken (heart rate), behavioural responses coded (facial expressions, gestures, reactions), questionnaires completed and interviews conducted. The couples also rate their own and their spouse's emotions during the conversation (to gauge how well they read their spouse's emotions). Trained raters then code the recorded conversation for a range of emotions such as disgust, contempt, belligerence, and validation. These measures are then correlated with the questionnaire and interview data to uncover the 'hidden emotional dynamics' of the relationship