Salience Based Hierarchical Spatial Representations

Salience Based Hierarchical Spatial Representations Hongbin Wang (Hongbin.Wang@uth.tmc.edu) Yanlong Sun (Yanlong.Sun@uth.tmc.edu) School of Health Information Sciences, University of Texas at Houston 7000 Fannin Suite 600, Houston, TX 77030 Abstract Unfortunately, different opinions exist about how a psychological space is encoded. In this article, we briefly outline an integrated theory of human spatial representations that is built on solid neuropsychological evidence and is able to accommodate several seemingly contradictory previous findings. The theory essentially states that a psychological space consists of multiple representations, each with a distinctive frame of reference and each being a partial selection (anchor-based) of all possible spatial information. The theory lays out a set of principles about what information is readily encoded in each representation and how different representations interact to solve spatial problems, which often lead to tested predictions in spatial performance. This article consists of three parts. In the first part, we will briefly review several key concepts and claims of the theory, including frame of reference and salience. Several major theoretical debates in the field are highlighted. In the second part, we report an experiment that was designed to test theory's claim on salience based hierarchical spatial representations. In the final part, the implications of the theory are discussed in the broad context of modeling human spatial cognition. How people represent space is a central issue in spatial cognition research and has profound implications on human performance in spatial tasks. In this article, we describe a theory of human spatial representations, which claims that space is represented in the brain and in the mind not once but multiple times, each being a map of salience with a distinctive frame of reference, and that human performance is determined by the interaction among multiple such representations. An experiment is reported to test the theory's claim on salience based hierarchical spatial representations. Introduction People live in a 3D world and perform various spatial tasks in every waking minute of their lives. Searching for an object in a visual scene, walking to your office from the parking lot, navigating in a new city, and surfing Google Earth, to name a few, all involve spatial information processing. Some tasks are easy while others are quite challenging. How and why is this so? Decades of interdisciplinary research on human spatial cognition has resulted in a range of theories, with each focusing on distinctive aspects (Freksa, Habel, & Wender, 1998; Golledge, 1999; Newcombe, 2002; O'Keefe & Nadel, 1978; Tolman, 1948). However, the role of spatial representations on human spatial performance has been almost universally emphasized (Klatzky, 1998; H. Wang, Johnson, Sun, & Zhang, 2005; R. F. Wang & Spelke, 2002). While it is generally accepted that any physical space has to be somehow digested and encoded in a psychological space in order to be cognitively useful, a large body of evidence has convincingly shown that a psychological space is not an exact copy of the corresponding physical space. On the one hand, a physical space appears perfectly three-dimensional, absolute, unified, continuous, and Euclidean. On the other hand, it is well documented that the psychological space is often segmented, relative, partial, distorted, and non- Euclidean (e.g., Halligan, Fink, Marshall, & Vallar, 2003; Hunt & Waller, 1999; McDonald & Pellegrino, 1993; Newcombe & Huttenlocher, 2000; Tversky, 2000). Because of this, if a spatial task requires a certain piece of information and if that piece of information is represented in a form that is not suitable for the task or not represented at all, then the task becomes more difficult. In contrast, if a task requires a piece of information that is properly represented and readily available, then the task often becomes easier. A Theory of Spatial Representations Any theory describing the representation of space has to solve at least two critical problems – how to represent and what to represent. The how problem has to do with the concept of frame of reference (FOR). In a certain sense, to represent a space is to encode the space in a frame of reference (FOR). Though different taxonomies exist (e.g., Brewer & Pears, 1993; Garnham, 1989; Klatzky, 1998; Levinson, 1996; Logan & Sadler, 1996; Palmer, 2002; Talmy, 1983), three classes of frame of reference can be generally distinguished – egocentric (where the FOR is centered on the observer or her body parts), allocentric (where the FOR is centered on an object external to the observer), and intrinsic. An intrinsic FOR is a blend of an egocentric frame and an allocentric frame in that in an intrinsic FOR, while spatial information is centered on a specific object other than the observer (similar to an allocentric frame of reference), it is coded in egocentric terms as if the observer is located at the same place and with the same heading as the object at the origin. An example is “John is sitting on Mary’s right”. Although different reference systems are theoretically equivalent in locating objects in a space, psychologically people acquire and utilize frames of reference quite differently. In which frame of reference psychological space