In the early 1970's, NBS developed a time distribution system that placed a hidden time code on an unused part of the television signal. A decoder in the television set recovered and displayed the time. While the system was not implemented, this technology provided the basis for closed captioning.
In 1971, NBS and ABC-TV began experimentally transmitting captions. A demonstration was held for the National Conference on Television for the Hearing Impaired, showing an episode of Mod Squad that had been captioned by a NBS employee, Sandra Howe.
In the following years, the Public Broadcasting System, working with NBS, took up the project and developed convenient encoding equipment and improvements to the captioning format.
In 1980, ABC, NBC, and PBS began transmitting closed captions on selected programs, and decoders went on sale to the public. This coincided with the establishment of the National Captioning Institute which is still responsible for much of today's captioning.
In September 1980, NBS, ABC, and PBS received Emmys from the Academy of Television Arts and Sciences for this development. The NBS staff (Dick Davis, Jim Jespersen, and George Kamas) responsible for the work were later invited to the White House to meet with President Carter and receive his congratulations.
In 1990, President Bush signed a bill requiring that all television sets 13 inches or larger sold in the U.S. after July 1, 1993 have the capability for displaying closed captions.
Closed captions on a television set appear as white on a black background. They can be on the top or bottom of the screen depending on the nature of the picture. In a typical captioned program, captions do not appear when printed text is on the screen or when there is no speech. All television sets are configured so that captions can be switched on or off. The standard format now being used allows for captioning in two languages, but single language captioning predominates today.