Keeping track of objects while exploring a spatial layout with partial cues: Location-based and deictic direction-based strategies

Résumé En

A growing interdisciplinary literature has been concerned with object cognition and its relation to deictic/indexical reference mechanisms. This literature postulates that explanation of many phenomena in perception requires appeal to interactions between agent and environment, and to the ways that sensory-motor information connects to cognition through deictic (or demonstrative) reference. In this paper we report a study of the ability to keep track of distal targets in informationally impoverished situations – in particular when only the direction of these objects is known and not their locations. This study introduces a new experimental paradigm called the Modified Traveling Salesman Problem. This task requires subjects to visit once and only once n invisible targets in a 2D display, using a virtual vehicle controlled by the subject. Subjects can only see the directions of the targets from the current location of the vehicle, displayed by a set of directional segments that can be viewed inside a circular window surrounding the vehicle. Two conditions were compared. In the “allocentric” condition, subjects see the vehicle move across the screen and change orientation under their command. The “egocentric” condition is similar except for how the information is provided: the position and orientation of the vehicle icon remains fixed at the center of the screen and only target directions, as indicated by the directional segments, change as the subject “moves” the vehicle and changes its orientation relative to the objects (but not relative to the screen). The unexpected finding is that this task can be performed, in either condition, for up to 10 targets. We consider two types of strategies that might be used, “location-based” strategies and “deictic direction-based” strategies. Location-based strategies rely on spatial memory and attempt to infer the locations of all the targets. Direction-based strategies rely on a deictic frame of reference and focus on the directional segments themselves, keeping track of the ones that represent already-visited or to-be-visited targets. A number of observations suggest that the direction-based strategy was used, at least for larger numbers of targets, which is consistent with the deictic approach. According to our hypothesis, keeping track of the directional segments requires the use of deictic strategies for tracking segments and associating them with their status in the task – given by current status predicates Visited(x) or Not-visited(x) – perhaps using visual indexes (Pylyshyn, 2001), deictic pointers (Ballard et al., 1997), or object files (Kahneman et al, 1992).