Dilution Effects in Perceptual Information Integration

Dilution Effects in Perceptual Information Integration Jared M. Hotaling a (jhotalin@indiana.edu), Andrew L. Cohen b (acohen@psych.umass.edu), Jerome R. Busemeyer a (jbusemey@indiana.edu), & Richard M. Shiffrin a (shiffrin@indiana.edu) a Department of Psychological & Brain Sciences, Indiana University 1101 E. Tenth St., Bloomington, IN 47408 USA b Department of Psychology, University of Massachusetts Amherst, MA 01003 USA optimal (Gilovich, Griffin, & Kahneman, 2002). The conjunctive fallacy, unpacking effects, and the dilution effect are just a few of the many common findings that violate normative models of information integration. These deviations from rational behavior are so numerous that it is now common to assume sub-optimal integration as a starting point for theories of decision making. Abstract In cognitive science there is a paradox: Researchers studying decision making have repeatedly shown that people employ simple and often less than optimal strategies when integrating information from multiple sources. However, researchers working in fields such as categorization, memory, and perception have had great success using optimal models to account for information integration. Is this conflict due to the use of different materials and procedures? We test the hypothesis that stimuli requiring more controlled information integration lead to suboptimal performance, while stimuli that lend themselves to more automatic processing produce more optimal integration. We test for one canonical example of sub-optimal information integration, the dilution effect, using stimuli more commonly found in perception experiments. Dilution was indeed reliable across several conditions. The largest effects occurred in stimuli manipulated so as to discourage automatic processing. We use the Multi- component Information Accumulation model to explain how stimulus presentation influenced cognitive processing. Optimal Integration in Perceptual Domains In contrast, there are numerous successful applications of optimal or rational models of information integration in domains such as perception (Oden & Massaro, 1978; Tenenbaum, 1999), categorization (Ashby & Maddox, 1990, 1992; Nosofsky, 1986), and memory (Anderson, 1991; Shiffrin & Steyvers, 1997). Researchers in these more perceptual fields begin with an assumption of optimal integration and only later investigate sub-optimal or heuristic-based strategies. Keywords: dilution effect; information integration; models The Dilution Effect Introduction Information integration is the combining of evidence from multiple sources. Many tasks, from speech comprehension to medical decision making, require such integration. Each source of information on its own provides some evidence, but integrating all information yields the best performance. This article investigates the manner in which information is combined. While the literature provides numerous examples of near-optimal information integration, there are just as many examples where it is far from optimal. The types of stimuli and procedures used often determined the pattern of results. Tasks involving quantitative stimuli, like probability judgments (Tversky & Kahneman, 1974), seem to implicate heuristic strategies, more than perceptual tasks, like speech comprehension (Oden & Massaro, 1978). Our research tests the hypothesis that even perceptual information can produce suboptimal integration if it is displayed in a way that discourages automatic processing. Suboptimal Integration in Decision Making Many studies of judgment and decision making suggest that information from multiple sources is integrated via simple heuristics. Sometimes these studies produce behavior approaching optimal decision making (Gigerenzer & Todd, 1999), but in many other cases, performance is well short of Although information integration is an object of study by researchers in both decision making and perceptual domains, these fields often seem to operate independently of each other. One reason is the difference in experimental paradigms. Decision making research focuses mainly on linguistic and quantitative stimuli, and is concerned with how individuals use information to form explicit inference or preferences. Perceptual research typically relies on more perceptual stimuli, and concentrates on how the information is produced from external stimulation. Even when words are used as stimuli, as in memory research, the focus of information integration often includes perceptual aspects of the stimuli. The present research aims to bridge this divide through a novel experimental paradigm that combines aspects of each research tradition. We focus on one example of sub-optimal information integration: the dilution effect. This effect refers to a situation where adding null or weak positive evidence to what is already strong positive evidence reduces the overall belief in a hypothesis. The effect has been replicated in numerous studies (LaBella & Koehler, 2004; McKenzie, Lee, & Chen, 2002; Nisbett, Zukier, & Lemley, 1981; Peters & Rothbart, 2000), but Shanteau (1975) gives one of the clearest demonstrations of the dilution effect. In his study, an experimenter drew samples of red (R) and white (W)