The initial segment strategy: A heuristic for route selection

JEREMYN 0 1 2 BAILENSON ) 0 1 2 MICHAEL S. SHUM 0 1 2 DAVID H. UTTAL 0 1 2 0 Portions of Experiment 5 were presented at the 20th annual meeting of the Cognitive Science Society and appear in its Proceedings. Por tions of this work were supported by Grant R29 HD 34929 from the National Institute for Child Health and Human Development and LIS Grant 97201313 from the National Science Foundation. We thank John Coley and Juliabeth Proffitt for their helpful comments , Elissa Larkin, Alex Okrent, Layla Piland, and Stephanie Sun for running subjects, preparing stimuli, and entering data, Leah Vaughn for entering data, and Eleanor Antonucci and Wanda Shum for guidance. Correspon dence concerning this article should be addressed to 1. N. Bailenson, Department of Psychology, University of California , Santa Barbara, CA 93106-9660 ( 1 Northwestern University , Evanston, Illinois 2 BAILENSON, SHUM, AND UTTAL People often choose one route when traveling from point A to point B and a different route when traveling from point B to point A. To explain these route asymmetries, we propose that people rely on a heuristic (the initial segment strategy, or ISS) during route planning. This heuristic involves basing decisions disproportionately on the straightness of the initial segments of the routes. Asymmetries arise because the characteristics that favor selection of a particular route in one direction will usually differ from those that favor selection when traveling in the opposite direction. Results from five experiments supported these claims. In the first three experiments, we found that subjects' decisions were asymmetric and involved a preference for initially straight routes. In Experiment 4, we confirmed that the ISS is a heuristic by demonstrating that people rely on it more when under time pressure. However, people can choose the optimal route when instructed to do so. In Experiment 5, we generalized the findings by having subjects select routes on maps of college campuses. Taken together, the results indicate that the ISS can account for asymmetries in route choices on both real and artificial maps. - A consistent finding in research on decision making and planning is that choices are often asymmetric. For example, people may judge that Cuba is more similar to the (former) Soviet Union than vice versa (Tversky, 1977). Asymmetries have been demonstrated in many different domains, including judgments of spatial distance (Holy oak & Mah, 1982; McNamara, 1991; McNamara & Di wadkar, 1997; Montello, 1991; Newcombe, Huttenlocher, Sandberg, & Lie, 1996; Sadalla, Burroughs, & Staplin, 1980), descriptions of networks (Denis & Cocude, 1989; Robin & Denis, 1991), and counterfactual reasoning (Dun ning & Parpal, 1989). Our focus here is on asymmetries that occur when plan ning routes between two locations. Several researchers have demonstrated that route selections are often asym metric; people consistently prefer a different route when traveling from location A to location B than when travel ing in the opposite direction. These path asymmetries have been observed in many different kinds of tasks, including people's planning of routes from maps (Bailenson, Shum, & Uttal, 1998; Christenfeld, 1995), drivers' recall ofroutes that they usually follow (Stem & Leiser, 1988), and pedes trian's selection of routes when traveling across a parking lot (Christenfeld, 1995) or along paths on a college campus (Shum, Bailenson, Hwang, Piland, & Uttal, 1998). Asymmetries in route selection are interesting because they involve a violation of what would seem to be a very important consideration in planning routes: the desire to take the shortest route. If people attempt to choose the shortest route and these attempts are successful, their se lections should rarely be asymmetric; the shortest route will be the same, regardless of direction. However, people do not always choose the shortest route (Bailenson et al., 1998; Christenfeld, 1995). Rather, they seem to rely on heuristics for selecting routes. These heuristics minimize cognitive effort and usually will lead to satisfactory route choices. However, one consequence of the reliance on heuristics, as opposed to a systematic search for the op timal route, is predictable asymmetries. In the present work, we delineate the conditions under which people do and do not rely on a heuristic that leads to systematic asym metries in route selections. Christenfeld (1995) proposed one heuristic for route selection: People defer route decisions for as long as pos sible. As is shown in Figure I, Christenfeld asked people to choose from routes that were identical in all aspects except the location along the route at which a turn was required. The layout of some possible routes required a turn early on, but on other routes, the turn could be deferred because of a long and straight initial segment. To mini mize mental effort, people selected the routes on which the turn occurred last. Use of this heuristic leads to asym metric decisions, because the route with the last tum will necessarily be different when traveling along a route in one direction than when traveling in the opposite direc tion. Christenfeld attributed his findings to the use of a domain-general decision-making heuristic for selecting among identical options. UJ 5 o a: N UJ 5 o a: Christenfeld's explanation adequately accounts for those situations in which the routes are identical except for the location at which a tum must be made. However, his model may not be applicable to many route choice sit uations. For example, two routes are rarely identical in all ways except the location of turns. Furthermore, people do not always have the option of delaying tum decisions. In many cases, the first route decision may be the only deci sion one has to make (i.e., deciding between two major highways for a long-distance trip). In these situations, there is no opportunity for people to delay decisions, yet asymmetries still occur (Shum et aI., 1998). The purpose ofthe present paper was to provide a more general account of the factors that lead to asymmetries in route selection. In this paper, as well as in previous work (Bailenson et aI., 1998), we suggest that people tend to focus dispro portionately on the initial portions of the routes (i.e., the segments near the origin). More specifically, people tend to make their route decisions on the basis of the straight ness of the initial segments. As used here, straightness means the relative absence of curves or turns. We call this preference for initially straight route segments the initial segment strategy (ISS). Given the choice between two routes, people will prefer the one that is initially more straight, regardless of what the later portions of the routes look like. Use of this heuristic leads to path asymmetries, because a route may be initially straight at one end (near the origin), but not at the other end (near the destination). Iforigin and desti (...truncated)