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Abstract

According to the hierarchical theories of spatial representations, places are grouped
together into regions which form higher level nodes of a graph-like representation of
space. Support for these theories comes from a wide variety of experiments using different
methods (distance- and directional judgments, priming, recall). However, the ultimate
purpose of an internal representation of space is to allow navigation, route planning, and
directed movements through the environment. To our knowledge it is still an open question
whether or not hierarchically structured spatial representations influence navigational
abilities such as route-planning behaviour of humans. By employing a navigational
task in a virtual environment we provide additional evidence for the hierarchical theories
of spatial representations, and their role in route planning. Subjects navigated through a
virtual environment that was presented on a large half cylindrical projection screen. They
learned the positions of twelve landmarks within the environment. According to the
object category of the landmarks, the environment could be grouped into three different
semantic regions. Subsequent to an exploration- and training-phase subjects were asked
to navigate the shortest route connecting three of the objects. All test routes featured two
alternative solutions of equal length that only differed in the number of region boundaries
they passed by. Subjects preferred routes that minimized the number of region boundaries
that were passed by. These results provide additional support for the hierarchical
theories of spatial representations. Additionally the findings suggest that route planning
is based on region-connectivity, not place-connectivity alone. We propose a planning
mechanism that uses coarse space information (region-connectivity) for the goal(s) and
fine space information (place-connectivity) for the current location. Such a planning
mechanism would reduce computational effort by using a graph theoretic distance measure,
i.e. the number of region boundaries crossed along a route.