Gestalt Effects in Planning: Rush-Hour as an example
Gestalt Effects in Planning: Rush-Hour as an example
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规划中的格式塔效应:以高峰时段为例
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发表时间:
2014
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通讯作者:
Lars Konieczny
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作者:
S. Bennati;S. Brüssow;Marco Ragni;Lars Konieczny
Gestalt Effects in Planning: Rush-Hour as an example Stefano Bennati (bennati@cognition.uni-freiburg.de) Sven Br ussow (sven@cognition.uni-freiburg.de) Marco Ragni (ragni@cognition.uni-freiburg.de) Lars Konieczny (lars@cognition.uni-freiburg.de) Center for Cognitive Science, University of Freiburg Abstract Planning problems have been extensively studied with regard to graph theoretical properties such as the number of steps nec- essary to reach a specific goal state or the size of the problem space. These structural properties, however, do not completely characterize a problem. In the presented eye-tracking study we also investigated the influence of perceptual factors on the solution to a planning problem. While not affecting the cor- rectness of a solution, the results suggest that certain Gestalt properties are responsible for the deviation from optimal plans. Keywords: Move planning; Rush-Hour; Gestalt Introduction Planning problems can be characterized by structural proper- ties, such as the number of steps necessary to reach a specific goal state or the size of the problem space, and perceptual properties, such as colors and spatial relations between ele- ments. While structural elements have been widely studied, the latter have not receive as much attention. The reason may be that structural properties are easier to manipulate than per- ceptual properties. The problem of our choice, Rush-Hour, can be easily manipulated with regard to perceptual proper- ties. Rush-Hour schematizes a crowded parking lot on a 6 × 6 grid (cf. Fig. 1) and the task is to clear the way for the player’s car which is blocked by some other vehicles. The player’s car is always red, horizontally aligned and placed in the third row, the same row where the exit is. There are two types of vehicles: cars (length two) and trucks (length three). Each vehicle has an orientation–vertical or horizontal–and a color. All vehicles can only be moved forward and backward along their longitudinal axes. The game rules forbid moving a vehi- cle over or through another vehicle or breaking the walls that surround the parking lot. The goal is to clear the way to the exit by sequentially moving the vehicles that block the way, which are in turn blocked by others. The game is well-defined, decomposable, non dynamic and has only one goal. It is also PSPACE-complete (Flake & Baum, 2002). There is normally more than one possible solu- tion, but only few of them are optimal. We define an optimal solution as the solution that involves the least possible num- ber of moves. Planning problems are often characterized by permutation problems. From a cognitive perspective planning can be de- fined as the anticipation of action steps or “a procedure for achieving a particular goal or desired outcome” (Morris & Ward, 2005). Figure 1: Rush-Hour sample configurations. The task is to rearrange the vehicles such that the red car can be moved out. Only the board on the left contains a cluster. Insights from different domains, such as Tower of London, indicate that difficulties arise from static properties such as planning depth, i.e., the number of moves necessary to trans- form the initial state into a goal state (Kaller, Unterrainer, Rahm, & Halsband, 2004; Kaller, Rahm, K¨ostering, & Un- terrainer, 2011). A relevant property of Rush-Hour is the number of vehicles on the grid, as it increases the search tree. Dynamic proper- ties, such as the number of counter-intuitive moves and the number of circular move sequences have an influence on dif- ficulty as well (Ragni, Steffenhagen, & Fangmeier, 2011). A move is counter-intuitive if it results in a higher distance to the goal state, for example when the goal car has to be moved away from the exit or into an exit-blocking position. A move sequence is circular if one of its vehicles is blocked by an- other vehicle that is part of the same move sequence. Human performance on two different boards with the same structural properties may differ. We propose that this differ- ence results from perceptual properties that affect problem solving and planning processes in a way that deserves deeper investigation. Gestalt Theory asserts that under certain conditions people perceive a group of distinct objects as a holistic unit. For example, when objects are aligned to each other or are in close proximity to each other, they will be perceived as parts of a bigger object (Koffka, 1935; K¨ohler, 1959; Wertheimer, 1938). With respect to the Rush-Hour domain, a cluster rep- resents a meta-object that groups together adjacent objects on the board: It is defined as a group of two or more vehicles that are next to each other such that their major axes are parallel (cf. Fig. 2). In this context, the Gestalt laws of proximity and