1. A method of measuring group behavior, comprising: using a low-light camera, an infra-red (IR) illuminator, and an IR bandpass filter to generate a uniform visible signal of a video stream comprising a sequence of images of a group having a plurality of members, wherein the group is exposed to a stimulus; detecting a response of each member of the group to the stimulus over a period based on the sequence of images of the uniform visible signal, wherein detecting the response of each member comprises: recognizing a facial motion of each member; and creating a body motion profile for each member by: extracting and registering each part of a body of each member; measuring a movement of each part of the body by measuring a three-dimensional (3D) displacement; and calculating a normalized motion for each part of the body; generating an aggregate response to the stimulus by aggregating the response of each member of the group; and generating a group behavior by determining an amount of synchrony of the response of each member relative to the aggregate response, generating the group behavior comprising: segregating the response of each member over the period into a plurality of responses over a first set of time intervals, each time interval of the first set of time intervals comprising a second set of time intervals; calculating an amount of synchrony among all members for each time interval of the second set of time intervals; determining a time interval of the second set of time intervals having the largest amount of synchrony among all members; finding a group response for each time interval of the first set of time intervals by summarizing responses of all members of the group over the time interval of the second set of time intervals determined to have the largest amount of synchrony among all members; and summarizing the group response for all the time intervals of the first set of time intervals.