Persuasion has been a major topic of study for scholars interested in attitude change (Eagly & Chaiken, 1993). Earlier cognitive theories focused on how people process the quality of persuasion messages (Greenwald, 1968; McGuire, 1968). For example, persuaнsion effects were conceptualized in terms of the attention allocated to the message, the compreнhension of the message content, and the accepнtance of the message conclusions (Hovland, Janis, & Kelley, 1953). Unlike these messagebased theories of persuasion, the Heuristic-Systematic Model (HSM)(Chaiken, 1980, 1987), together with the Elaboration Likeliнhood Model (ELM)(Petty & Cacioppo, 1981, 1986b), recognized a host of variables concepнtually independent of message quality that inнfluence people. Most important, according to both the HSM and the ELM, these variables can trigger qualitatively different information processing.

Although people can carefully attend to and elaborate on the content of a persuasion message, they can also process the message quite superficially, attending only to cues peripheral to its content such as the length of the message and the source of the message. The HSM attempts to characterize these two modes of processing—systematic and heurisнtic—and to specify the conditions that trigger and govern a specific mode of processing. We hasten to add that the two modes of informaнtion processing (systematic vs. heuristic) are not linked in one-to-one fashion with the types of informational cues (message content vs. other cues), as suggested by some reнsearchers (Kruglanski & Thompson, 1999). The critical assumption of the HSM is that people can engage in systematic or heuristic processing. People can scrutinize cues periphнeral to the message content, or they can proнcess the message content heuristically. The