Planning with Information Access Costs in Mind

Planning with Information Access Costs in Mind Samuel M. Waldron (waldronsm1@cardiff.ac.uk) John Patrick (patrickj@cardiff.ac.uk) Department of Psychology, Park Place Cardiff, CF10 3AT UK Andrew Howes (howesa@manchester.ac.uk) Geoffrey B. Duggan (geoffrey.duggan@manchester.ac.uk) Department of Informatics, PO Box 88, Sackville Street Manchester, M60 1QD UK Abstract Least effort tradeoffs concerning the use of memory within the Blocks World Task (Fu & Gray, 2000) are extended to an analogous problem solving task. As the cost of accessing goal-state information from the Blocks Problem Solving Task increased, participants chose to access such information less frequently, and in turn, made more problem solving moves per goal-state visit. This strategy shift led to an increase in the number of moves required to solve each problem, suggesting that effective planning became difficult as the access cost increased. In contrast, increasing the implementation cost, a manipulation known to increase planful behavior (O’Hara & Payne, 1998), revealed quite different problem solving access strategies, and reduced the number of moves required to solve each problem. Keywords: Interactive behavior; Human problem solving; Information access; Adaptive planning. Introduction Problem solving is often conducted within the context of an external display (Larkin, 1989; Payne, 1991). However, the time, physical effort, and mental effort associated with accessing information from such displays may vary. For example, information may be available at the click of a button, or considerable time and effort may be required in order to extract the necessary information from the interface. Such information access costs have been shown to determine what perceptual-motor and memory strategies are used during interactive behavior (Fu & Gray, 2000; Gray & Fu, 2004), but have yet to be extended to problem solving. The current paper aims to test for the presence of shifts in strategy due to information access cost during problem solving, and assess consequences for planning proficiency. Planning Research assessing the manner in which humans go about planning has informed us that planning and acting are largely interleaved (Anderson, 1990). That is, we do not plan complete sequences before we perform them. Rather, we evaluate our plans as we progress through the problem space. Typical planning behavior is said to be opportunistic (Hayes-Roth & Hayes-Roth, 1979), in the sense that plans can be revised in the face of new information, or as a consequence of an evaluation of a previous plan. The proposed benefits of planning have also been found to interact with the limited capacity of working memory (Kotovsky, Hayes, & Simon, 1985; Phillips, Wynn, Gilhooly, Della Sala, & Logie, 1999). Moreover, problem solving within the context of an external display has been shown to be sensitive to costs within the environment. O’Hara & Payne (1998) stated that “problem solving search strategies are chosen so as to optimize performance within the constraints of a particular situation” (p.34). Gray & Fu (2004) recast this assertion by distinguishing between hard and soft constraints. Hard constraints determine behavior that is, or is not possible, whereas soft constraints bias towards certain behavioral strategies. An example of a soft constraint that promotes planfulness within a problem solving context is the implementation cost. Using the 8-Puzzle, O’Hara & Payne (1998) demonstrated that increasing the cost of making each move from pressing a function key to typing a string increased participant’s propensity to plan ahead, and in turn, reduced the number of moves needed to complete the task. Evidence of planfulness came mainly from increased latencies between each move. Verbal protocol analysis also suggested more planful behavior as a function of increased implementation cost. Thus, it appears that the extent to which problem solvers choose to plan can be partially determined by costs within the environment associated with completing the task. Information Access Cost The planning research briefly reviewed above assumes that the information needed to solve a problem is either readily available in the world, or is held in memory. For example, the 8-Puzzle goal-state used by O’Hara & Payne (1998) is so easy to maintain in memory that participants were not required to search for additional information in order to solve the problem. For the vast majority of other problem solving tasks (e.g., Tower of Hanoi, Missionaries & Cannibals, Water Jugs), all task-relevant information is provided within the external display with little or no associated access cost. The converse, however, is often true of problem solving in many applied situations. That is, the information required