Two samples, the first consisting of 13 and 16-year-olds and adults, the second consisting of children from kindergarten, second and sixth grades, are interviewed to measure the cognitive processes used to evaluate the credibility of television content. Additional goals include measuring the relationship between the use of these cognitive processes and the degree of credibility ascribed to television content or the degree of attitude change, taking into account sex, age, and ethnic background. Six cognitive processes are found which belong either to information sources outside television or to information about the industry itself. It is found that conceivability is the most frequently used source of information outside of television, and information about the television industry itself the most frequently used among television-related information sources. (WBC)