Types of Evidence and Routes to Persuasion: The Unimodel Versus Dual-Process Models

Following the pioneering research of Hovland and his colleagues in the 1950s (e.g., Hovland & Janis, 1959; Hovland, Janis, & Kelley, 1953; Hovland, Lumsdaine, & Sheffield, 1949), social psychologists have proposed a variety of specific “process” models of persuasion to explain how the plethora of source, message, recipient, and context factors produce changes in attitude (for reviews, see Eagly & Chaiken, 1993; Petty & Wegener, 1998). Most investigators, however, would seem to accept the more general proposition that persuasion can occur through one of two qualitatively different “routes.” Both Petty and Cacioppo’s (1986) Elaboration Likelihood Model (ELM) and Chaiken’s (1987; Chaiken, Liberman, & Eagly, 1989) Heuristic Systematic Model (HSM) distinguish between persuasion based on careful scrutiny of the merits of the message arguments and persuasion that results from the processing of any of a variety of nonmessage factors such as source cues. The distinction between cues and heuristics and message arguments is fundamental in dual-process models of persuasion, for these two categories of variables covary (in prior research; e.g., Petty, Cacioppo, & Goldman, 1981) with several factors that mediate persuasive outcomes (e.g., information length, complexity, accessibility, order of presentation, and relevance). Moreover, dual-process models imply that levels of motivation and ability determine whether persuasion is mediated by cues and heuristics or by message arguments, which in turn determines the extent to which postmessage attitudes are enduring and consequential (e.g., Petty & Cacioppo, 1986; Petty, Haugtvedt, & Smith, 1995). More specifically, in the dual-process literature there is an implied relation between the amount of thinking the recipient engages in and the object(s) on which that thought is projected (e.g., message arguments, source characteristics). “Deeper,” more effortful thinking occurs when considering the cogency of the message arguments, whereas “shallow” or less effortful thinking occurs in relation to nonmessage features of the persuasion situation. Underlying this implicit covariation between content and process is the assumption that cues and heuristics and message arguments importantly differ in terms of such persuasion-relevant factors as informational length, complexity, and relevance. Because message arguments are thought to be (or at least are typically operationalized as) longer, more complex, and more relevant to persuasive conclusions than cues and heuristics, persuasion based on the former is believed to (a) require higher levels of processing motivation and ability, (b) confer more judgmental confidence, and (c) produce more consequential (i.e., stronger) attitudes than persuasion based on the latter. Although some of these differences between cues and heuristics and message arguments have not been directly tested (e.g., whether message arguments are inherently longer and more complex than cues and heuristics), there is ample support for many of these distinctions in the ELM and HSM literatures (e.g., the differential impact of motivation and ability on the processing of cues and heuristics and message arguments). Kruglanski and Thompson’s provocative article represents a fundamental challenge to this dual-process conceptualization of the persuasion process. There are two important aspects to their claim: First, they argue that in most ELM and HSM studies, the cue–message distinction has been inadvertently confounded with key persuasion parameters such as length, complexity, order of entry, and relevance. They argue that this chronic conflation in prior research is responsible for both the differential impact of motivation and ability on the processing of cues and heuristics versus message arguments (e.g., Petty et al., 1981), and for the finding that persuasion based on message arguments yields stronger attitudes than persuasion based on cues and heuristics (for a review, see Petty et al., 1995). Kruglanski and Thompson argue that persuasion is mediated by the quality of the processed information—its length, complexity, relevance, accessibility, and so forth—and not whether its contents happen to be cues and heuristics or message arguments. Specifically, Kruglanski and Thompson argue that difficult-to-process information (of either the cue or heuristic or message argument type) mediates persuasive outcomes when motivation and ability are high and that easy-to-process information (of either type) will prevail under low motivation or ability conditions. Similarly, they propose that strength-related outcomes (i.e., an attitude’s persistence over time, its resistance to change, and its relation to behavior) depend not on whether the information is cueor argument-based, but on the depth and extensiveness of the recipient’s processing. In sum, Kruglanski and Thompson contend that the ostensible cue–message effects observed in dual-process studies are epiphenomenal.