The challenge and threat hypothesis states that people perform worse on complex tasks and better on simple tasks when in the presence of others because of the type of cardio-vascular response to the task. When performing a simple task in the presence of others, people show a normal cardiovascular response. However, when performing a complex task in the presence of others, the cardiovascular response is similar to that of a person in a threatening position. The normal cardiovascular response serves to improve performance, but the threat-like cardiovascular response serves to impede performance.