Spatial Updating in Intrinsic Frames of Reference

Spatial Updating in Intrinsic Frames of Reference Yanlong Sun (Yanlong.Sun@uth.tmc.edu) Hongbin Wang (Hongbin.Wang@uth.tmc.edu) Todd R. Johnson (Todd.R.Johnson@uth.tmc.edu) The University of Texas Health Science Center at Houston Houston, TX 77030 USA Abstract The present study investigates the properties of the spatial updating in terms of intrinsic frames of reference. We hypothesize that the efficiency of dynamically updating object-to-object relations is based on two main factors, a relatively stable frame of reference provided by the orienting object (or object array), and the behavioral significance (salience) level of the target objects. Three experiments were conducted using tasks of direction pointing. It was found that responses were significantly slower when the orienting object was constantly rotating. Given a relatively stable frame of reference, responses to the salient objects were faster than those to the non-salient objects when the number of salient objects was limited. The salience effect disappeared and re- appeared in the absence and presence of a stable frame of reference, respectively. These findings indicated that spatial updating in intrinsic frame of reference is not automatic and is limited by the number of target objects. Introduction As people move through an environment, they continuously update the spatial relations between themselves and the environment and the relations between the objects in the environment. For instance, a pedestrian who is waving on a taxi may also notice that a dog is chasing the taxi from behind. In this scenario, two kinds of information have to be encoded by the pedestrian, the relation between his body and the taxi, and the relation between the taxi and the dog. In fact, this example illustrates the distinction between an egocentric reference system (body-centered) and an allocentric reference system (more specifically in this scenario, an object-centered intrinsic system). It has been generally agreed that in encoding spatial information, different reference systems can be involved. Many researchers adopted the distinction between egocentric and allocentric reference systems and conjectured that participants in their experiments used either one of such systems (e.g, Bryant & Tversky, 1999; Diwadkar & McNamara, 1997; Franklin & Tversky, 1990; Shelton & McNamara, 1997; Sholl & Nolin, 1997; Simons & R. Wang, 1998. For a recent treatment, see McNamara, 2003, and Mou & McNamara, 2002). A large body of research has been focusing on spatial updating with respect to the egocentric system. It has been indicated that spatial memories are primarily egocentric and updating by the egocentric system is of high fidelity and automatic (e.g., Rieser, 1989; Shelton & McNamara, 1997; Simons & R. Wang, 1998; R. Wang, 1999). Nevertheless, Mou and McNamara (2002) and McNamara (2003) recently proposed that spatial information is encoded primarily of object-to-object spatial relations, and therefore is allocentric. This new theoretical framework calls for a systematic study on properties of spatial updating in intrinsic systems in dynamic situations, as compared to updating in egocentric systems. For example, Sholl and Nolin (1997) and R. Wang (1999) have suggested that egocentric self-to-object spatial relations are updated automatically as people move through an environment. It remains unclear whether updating in intrinsic frame of reference is also automatic. Furthermore, what kind of information is to be updated in intrinsic systems? Are all objects in the environment being updated with equal priorities? The present paper attempts to answer these questions by reporting three experiments. Our working hypothesis on spatial updating in intrinsic frame of reference is that such a process involves paying attention to both the orienting objects that anchor the intrinsic frame of reference and the target objects in their relations to the orienting objects. In other words, there are two sequential components in such a process: establishing and maintaining a frame of reference, then, updating the object-to-object relations. Thus, we hypothesize that updating in intrinsic systems can be achieved dynamically only when a relatively stable frame of reference can be maintained. In the taxi example above, in order to update the relations between the taxi and the dog, the pedestrian first needs to identify the orientation of the taxi. Second, we hypothesize that updating of object-to-object relations is affected by the behavioral significance of the target objects. This hypothesis is based on previous findings that visual selection can be prioritized by the object’s properties, by its specific location and background (e.g., Duncan, 1984; Wolfe, 1994), or even by cues in time (e.g., Watson, Humphreys, & Olivers, 2003). In the taxi example, a dog chasing the taxi probably is more salient than other objects on the street (say, a post stand), thus it is more likely to be