Reading for pleasure, which has declined among young people in recent decades, enhances thinking and engages the imagination in a way that visual media such as video games and television do not, Greenfield said.

"No one medium is good for everything," Greenfield said. "If we want to develop a variety of skills, we need a balanced media diet. Each medium has costs and benefits in terms of what skills each develops."

"Studies show that reading develops imagination, induction, reflection and critical thinking, as well as vocabulary," Greenfield said. "Reading for pleasure is the key to developing these skills. Students today have more visual literacy and less print literacy. Many students do not read for pleasure and have not for decades."

New York

In 1962, 77% of a Gallop Poll respondents said they had watched television the day before; in 1988, 91% admitted doing so. Nowadays "an average American spends at least three hours a day in front of a television set" (Glenn 223). Considering the impact of television on reading only in terms of time, conventional wisdom has it that television has a detrimental influence on the development of a person's literacy level simply because that people have allocated less time on reading. Thus it is not surprising for the general public to have the notion that Americans' reading habits are on the decline. Such view is reinforced by the popularity of such books as Jonathan Kozol's Illiterate America, in which Kozol states that more than one-third of American adults cannot read successfully. David Harman, the author of Illiteracy: A National Dilemma, observes that "more and more working members of mainstream America are found to be either totally illiterate or unable to read at the level presumably required by their job or their position in society."

Each additional hour of TV that toddlers watch per week translates into poorer classroom behavior, lower math scores, less physical activity, and more snacking at age 10, according to a new study in the Archives of Pediatrics and Adolescent Medicine.

Another theory is that the act of watching television can harm developing brains. A child's brain triples in size within the first three years of life in response to external stimulation, says Dr. Dimitri Christakis, M.D., a professor of pediatrics at the University of Washington and the country's foremost expert on the health effects of TV in childhood.

"Early exposure to [television] can actually be over-stimulating for the developing brain, and that can lead to shorter attention spans [and] cognitive difficulties," says Christakis, the author of "The Elephant in the Living Room: Make Television Work for Your Kids."