History of TV Laugh Track

Slate has a video-illustrated history of behind-the-scenes laughter: "Early television audiences expected their comedies to come with laughter, as laughter had been a fixture of radio comedies. The laughter, though, was live, and it was as much for the performers as for the TV-watching audience. Many of the earliest TV and radio comics had come up through vaudeville, and the idea of performing to an empty studio was alien to them."