Costs of switching perspectives in route and survey descriptions

Costs of Switching Perspectives in Route and Survey Descriptions Paul U. Lee (pauly@psych.stanford.edu) Department of Psychology, Bldg. 420 Stanford, CA 94305 USA Barbara Tversky (bt@psych.stanford.edu) Department of Psychology, Bldg. 420 Stanford, CA 94305 USA Abstract Two experiments examined perspective switching in comprehension and retrieval of spatial information. Participants read route or survey descriptions of environments line by line. Reading times were recorded. For half of the descriptions, the perspective of the last sentence was switched. True/false verification of sentences from both perspectives followed the descriptions. Switching perspective increased reading times but increased verification times only for survey sentences. This suggests that perspective switching exacts a cost in comprehension, but that the cost dissipates after information retrieval, especially for route descriptions. The second study examined which aspects of perspective, viewpoint or terms of reference, accounted for switching costs by using hybrid descriptions. Switching terms of reference slowed reading times more than switching viewpoint. Together, the experiments suggest that switching perspective plays a role in comprehension that diminishes with repeated retrieval. They also point to a fundamental asymmetry between route and survey perspectives, one that depends on orientation. Introduction All animals, human or otherwise, must be able to gain knowledge about their surroundings in order to survive. Like other animals, humans often gain this knowledge first-hand by navigating through their immediate surroundings. However, unlike other animals, humans also have the ability to transmit this knowledge to others by language. Whether the world is experienced first-hand or through descriptions, the world is viewed from a particular perspective. In text comprehension, maintaining a consistent perspective makes the text more coherent and comprehensible to the readers (Black, Turner, & Bower, 1979). Although there is a general agreement that we perceive the world from specific viewpoints, the role of perspectives on spatial memory is less certain. In particular, there is a considerable debate about whether or when spatial relations are encoded independently of perspective. If spatial memory is formed in a perspective- dependent manner, it should be more accessible from one perspective over the others. Therefore, when people describe spatial layouts from memory, they should prefer to maintain a consistent perspective in their descriptions since memory associated with a specific perspective is more accessible than others (Levelt, 1982). There is some evidence that supports this view. When readers take a particular viewpoint during text comprehension, they later remember the information better from that viewpoint (Black, Turner, and Bower, 1979; Abelson, 1975). Other evidence suggests that for constrained well- learned environments, spatial memory can equally be accessible from multiple perspectives. Taylor and Tversky (1992) demonstrated that when people learned route or survey descriptions of spatial layouts and later were asked inference questions about them, they were as fast and accurate to questions from the read perspective as from the new perspective. In spontaneous descriptions of naturalistic environments, people mixed route and survey perspectives about half the time (Taylor & Tversky, 1996). The choice of a perspective also seems to depend on the pragmatics of the situation much more than an inherent bias toward any particular perspective. During a conversation, speakers often use not only their own perspective, but also the perspective of their addressee’s or some perspective independent of both (Schober 1993; Tversky, Lee, & Mainwaring, 1999). In visual cognition, there is a similar inquiry about the nature of spatial memory derived from perception and navigation. There is some evidence that spatial relations are encoded in a viewpoint-dependent manner (Diwadkar & McNamara, 1997; Shelton & McNamara; Rieser, 1989). For example, Diwadkar and McNamara (1997) had participants study the locations of objects in a room from a single perspective and then learn to recognize the layout from three other views. A recognition test of the layout from different viewpoints showed faster response times for the learned viewpoints than the novel viewpoints. However, memories of large-scale spaces seem to encode spatial relations in a viewpoint-independent manner, in which familiar and