Television differs in several ways from books that may affect cognitive structures and processes. As with books, television can employ pictures, diagrams, and other representational symbol systems but in TV these symbols are transient and able to depict motion. While linguistic information in television can be orthographic, more often it is oral and, as with audiotape and radio, transient. Because in television, linguistic and pictorial symbol systems are transient and because they are presented simultaneously, it is possible that viewers process this information in a very different way than the back-and-forth serial processing of linguistic and representational information in books. It is also possible that the symbol systems used and their transient nature affects the mental representations created with television.
Television's window of cognitive engagement. While popular notions of TV viewing portray children as staring zoombie-like at the screen, reality is much different. When alternative activities are available, children generally look at and away from the TV between one and two hundred times an hour (Anderson & Field, 1983). Visual attention increases from very low levels during infancy to a maximum during the late elementary school years, declining somewhat during adulthood (Anderson, et al., 1986). Although the median look duration is usually only several seconds, extended episodes as long as a minute are not rare. Looks as long as ten minutes are exceptional. This discontinuous, periodic attention to a medium whose information streams by ceaselessly has important implications for comprehension and learning.