Human Spatial Reorientation using Dual Task Paradigms

Human Spatial Reorientation using Dual Task Paradigms Kristin R. Ratliff (k.ratliff@temple.edu) Department of Psychology, 1701 N. 13 th Street Philadelphia, PA 19122 USA Nora S. Newcombe (newcombe@temple.edu) Department of Psychology, 1701 N. 13 th Street Philadelphia, PA 19122 USA geometric properties of the space and handedness (short versus long walls to the left or right in the rectangle); however, the rats did not use other kinds of featural information, such as a colored wall or patterned corners, which would allow them to distinguish the correct corner. Hermer and Spelke (1994, 1996) found similar results using human children, 18 to 24 months. Based on these results, the geometric module hypothesis was proposed, suggesting that the geometric coding abilities of rats and children are encapsulated. Hermer-Vazquez, Spelke, and Katsnelson (1999) extended the geometric module hypothesis by claiming that the module is only seen among humans in children, due to their lack of a developed spatial language. Replicating the Cheng orientation task with human adults, Hermer-Vazquez et al. found that adults show no encapsulation, in that they use both the geometry of a room and the featural landmark cue of a colored wall to successfully reorient in a rectangular enclosure. They proposed that acquiring language, specifically production of the spatial terms “left” and “right”, may be necessary and sufficient for integrating geometric and featural information. Applying a selective interference design to further probe the necessity of language, Hermer-Vazquez et al. (1999) found that adults simultaneously performing a verbal shadowing task behave like children and rats, searching between two geometrically equivalent corners when reorienting in a rectangular room with one colored wall. However, when adults performed the reorientation task while simultaneously performing a nonverbal rhythm- clapping task, they successfully integrated the information from the two domains. These results support their conclusion that language is necessary for the integration of geometric and featural spatial information, allowing adults to overcome the encapsulation of the geometric module. Abstract After disorientation, human adults reorient within a symmetric geometric environment using featural information as well as the shape of the surrounding space, whereas children younger than 6 years do not. The hypothesis that use of features is due to language has been supported by findings that human adults behave like children when reorienting while performing a linguistic shadowing task (Hermer-Vazquez, Spelke, & Katsnelson, 1999). In this study we conducted a replication of the Hermer-Vazquez et al. (1999) Experiment 1, together with a condition involving more explicit information regarding the nature of the task. In this study, we also added a condition involving a spatial secondary task. Successful reorientation was more common in the explicit condition than in the exact replication, although above chance even in the latter. Reorientation was lowest for participants performing the spatial secondary task. These results provide evidence against the idea that language is necessary to overcome the encapsulation found among children and rats when trying to integrate geometric and featural information. Keywords: Spatial cognition; navigation; modularity. Introduction To functionally navigate through the environment, humans and animals rely on two systems of spatial adaptation: the egocentric “dead reckoning” system, whereby the organism uses the location of the self as the key to spatial orientation, and the allocentric system, whereby the surrounding environment provides landmarks for the organism to measure distance and direction to code location (Newcombe, 2002). The allocentric system itself can be further reduced to two types of spatial information by distinguishing between geometric and nongeometric information. The shape of a landmark is typically regarded as geometric information, while all other characteristics of the landmark, such as color, texture, and size, are regarded as nongeometric or featural information. Cheng (1986) examined how disoriented rats utilized geometric and featural information to reorient themselves and find food, which was hidden in one corner of a rectangular enclosure. Rats can no longer use dead reckoning once disoriented and must rely on their allocentric spatial system. Cheng found that the rats searched for the food at the geometrically equivalent corners in the rectangular room, suggesting that rats encode the Evidence Against the Geometric Module Recent animal research has cast doubt on the existence of a geometric module by examining various species capable of integrating geometric information along with featural landmarks to locate hidden objects. Additionally, these results raise more questions for the language modulated geometric module hypothesis, in that these nonhuman species definitely do not have linguistic capabilities to integrate the two forms of spatial information.