Spatial Memory for Highly Familiar Environments

Spatial Memory for Highly Familiar Environments Julia Frankenstein (julia.frankenstein@tuebingen.mpg.de) Tobias Meilinger (tobias.meilinger@tuebingen.mpg.de) Betty J. Mohler (betty.mohler@tuebingen.mpg.de) Heinrich H. Bulthoff (heinrich.buelthoff@tuebingen.mpg.de) Max-Planck-Institute for Biological Cybernetics Spemannstr. 38, 72076 Tubingen, Germany Abstract In this experiment we examined orientation dependency in human memory for a highly familiar environmental space. Twenty-seven inhabitants living for at least two years in Tubingen saw a photorealistic virtual model of the city center (Virtual Tubingen) through a head-mounted display. They were teleported to five different initial locations in Virtual Tubingen and asked to point towards well-known target locations. This procedure was repeated in twelve different body-orientations for each of the initial locations. Participants pointed more accurately when oriented northwards regardless of the initial location. We also found a small effect of local orientation. The more participants were aligned with the street leading to the target location the better was their pointing performance. Even though the strong alignment effect with a global orientation is predicted by reference direction theory, this theory does not predict that this global orientation is, first, common for almost all participants, and second, that this orientation is north. We discuss our results with respect to well-known theories of spatial memory and speculate that the bias we find for north orientation is due to participants relying on memory of a city map of Tubingen for their pointing response. Keywords: spatial memory; reference frame; environmental space; reference direction; view dependent; orientation independent; alignment; map Introduction In a familiar environment our spatial memory is needed for us to perform daily tasks. We must remember where our work is located, the route to travel there from our home, and we also need to be able to calculate a detour on occasions when our route is obstructed. A lot of spatial processes likely require a mental representation of our environment. The question addressed in this paper is how highly familiar environments are represented in memory. Theories of Spatial Memory There are many theoretical positions concerning the organization of spatial memory (e.g., Burgess, 2006; Gallistel, 1990; O’Keefe & Nadel, 1978; Rump & McNamara, 2007; Wang & Spelke, 2002). Most theoretical positions can be categorized with regard to their prediction of whether humans store their environment orientation dependent with respect to one or more reference directions, orientation dependent with respect to experienced views, and/or orientation independent. Reference Direction Theory. Reference direction theory states that humans store their spatial knowledge of the environment with respect to one or more reference directions. This theoretical position is mainly supported by McNamara and colleagues (e.g., Kelly, McNamara, Bodenheimer, Carr & Rieser, 2008; Mou, Xiao & McNamara, 2008; Shelton & McNamara, 2001; Rump & McNamara, 2007). The theory states that when learning a new environment, its spatial structure is stored in the specific orientation of a reference direction, whose orientation is determined by either the initial exposure to this environment (e.g., the first view of a room), or by its most salient orientation (intrinsic axis, e.g., parallel to the longer walls of a rectangular room). Initially reference direction theory was only tested in vista spaces. Vista spaces are spaces which could be explored from one point of view, e.g., one single room (see Montello 1993). Spaces such as our city of residence are considered environmental spaces. This kind of space could not be explored from one single point of view, by definition it contains at least two vista spaces which need to be integrated. McNamara, Slucenski and Rump (2008) extended the reference direction theory for environmental spaces, proposing hierarchical reference systems at different scales. Higher-order reference systems (e.g., for a city district) define the spatial relations between lower-order reference systems (e.g., for single streets). By learning an environmental space, humans encode multiple local reference systems with local reference directions. These local reference systems become part of a higher-order reference system by aligning their local reference directions to a single reference direction common for the whole environment. This global reference direction likely differs between individuals, i.e., there is no a priori reason to assume that all individuals should necessarily come up with the same global reference direction. According to this theoretical approach, humans should perform spatial tasks within a highly familiar environment best when they are aligned with the reference direction they use to store the whole environmental space. View Dependent Memory. Theories proposing a view dependent memory assume that all parts of the environment are stored in the local orientation in which they were explored (e.g., Cartwright & Collett, 1983; Christou & Bulthoff, 1999; Gillner, Weis & Mallot, 2008; Simons & Wang, 1998; Trullier, Wiener, Berthoz & Meyer, 1997;