Closed captioning can even be used as a convenience device by viewers who mute their TV to take a phone call but activate closed captioning to continue the program dialogue. Some newer television receivers automatically display this captioning when the mute button is pushed.

Perhaps the most novel use of closed captioning occurs in restaurants and bars where television sets are on but the audio portion is muted. Many bars will have multiple sets tuned to one or more channels of interest to their clientele. These channels might include the cable sports network ESPN, the cable news outlets CNN and CNBC, or various local stations.

The captions are “closed” to the general viewing audience because television producers believe that a continuous display of alphanumeric data across a TV screen is distracting and bothersome to the majority of viewers who are capable of following the dialogue aurally. Any viewer can choose to “open” the closed captioning, either by activating a switch on newer television sets or by using a separate decoder with older television sets that do not include the necessary decoder circuitry.

The decoder circuitry is designed to “read” the closed captions embedded in the vertical blanking interval. The vertical blanking interval is that 21-line portion of the 525-line National Television Systems Committee (NTSC) television signal that does not contain picture information. Various lines are used to carry technical data, and one of these lines is specifically reserved for closed captioning. The Advanced Television Systems Committee (ATSC) digital television signal carries closed captions as part of that signal’s data bit stream.

The concept for closed captioning was conceived in 1971 by engineers at the National Bureau of Standards. Further development involved WGBH-TV, the Boston public television station; Gallaudet University, the leading U.S. university for the hearing impaired; and the National Technical Institute in Rochester, New York. In 1976 the Federal Communications Commission (FCC) formally authorized the use of line 21, the last line of the vertical blanking interval, for this purpose.

Closed captioning received a major boost with the passage of the Television Decoder Circuitry Act of 1990. This law mandated the inclusion of closed-captioned circuitry in every television receiver with a screen of 13 inches or more that was manufactured, assembled, imported, or shipped in interstate commerce beginning July 1, 1993. Most receivers sold prior to that date did not include the circuitry, and viewers who wanted to access closed captions were required to purchase a separate decoder box for approximately $160.

The National Captioning Institute, an independent, nonprofit corporation, worked with engineers to develop an inexpensive electronic chip that could perform the same function as the cumbersome decoder boxes. This chip, if included in every TV receiver, would cost as little as $5, and this expense would presumably be absorbed into the total production cost of the sets. Citizen groups representing the hearing impaired lobbied Congress to enact legislation requiring the inclusion of a decoder chip in all receivers. Some opposition from manufacturers’ groups was voiced during congressional hearings, but the overwhelming number of those testifying supported the legislation. The bill passed both the House and the Senate and was signed into law October 15, 1990.

Closed captioning is program dependent, and not all programs are captioned. Most network and syndicated programs are captioned, however, and the percentage continues to grow. Locally produced programs are less likely to be captioned since stations lack the technical and financial resources to provide this service. Most cities do have one or more local newscasts with captions. Initially, the cost of this service was underwritten by a local health care provider or a charitable foundation. More recently, a number of advertisers have been willing to underwrite the cost in exchange for an announcement or credit at the end of the program.

Captions appear in either “roll-up” or “pop-up” fashion. The captions roll up the screen if the program is being aired live. Live captioning is done by skilled professionals using court stenographic techniques who can transcribe speech as rapid as 250 words per minute. The lag time between the spoken word and the caption is one to five seconds. The captions are not always word-for-word transcripts, but they do closely approximate the verbal message.

Pop-up captions are used for prerecorded programs and for commercials. These captions can be prepared more leisurely and are timed to match the flow of dialogue on the TV screen. Also, an attempt is made to place the caption under the person speaking at the time. In a two-person dialogue, the caption would pop-up on either the left or right half of the screen depending on the position of the speaker. Various icons are used to symbolize sounds; for example, a musical note is placed next to the caption when a person is singing.

The most challenging captions involve live sports coverage since there is no way to anticipate what program participants will say. Newscasts are less difficult because the same TelePrompTer that cues on-air talent also cues the person preparing the captions.

Since the captions are encoded as part of the electronic signal, a closed-captioned program may be transmitted in any form: over-the-air broadcast, satellite, cable, video cassette, or video disc. Programs containing captions are noted with a (CC) following the program title in TV Guide and similar listings.