9222002 MCNAMARA This research will investigate aspects of human memory. One line of experiments will investigate the nature of spatial memory. A series of nine experiments will attempt to determine whether spatial memories are "orientation specific" or "orientation free." In orientation-specific representations, locations are specified in view-specific reference frames and the representation has a canonical orientation. One's memory of a map or of the globe is an example of an orientation-specific representation because it is oriented with north at the top. Orientation-free representations, on the other hand, are not view dependent and do not have a canonical orientation. An example of such a representation is memory of the interior of one's home; such memories typically do not have a canonical orientation. An obvious difference between these types of memories is the number of perspectives we had on the spatial layout when it was learned (typically only one for a map, but several for natural environments). The experiments will test this explanation and other explanations of the differences between memories of small- and large-scale spaces. Another series of four experiments will investigate the causes of asymmetries in distance estimations. Previous research has shown that when people estimate distances from memory, estimates from salient landmarks to less salient locations (e.g., from the Washington Monument to the Pension Building) are larger than estimates from the less salient building to the landmark. The goal of the proposed experiments is to determine why these asymmetries occur. These studies of spatial memory will provide crucial new knowledge about the basic mechanisms that underlie our ability to recognize scenes and to navigate in familiar and unfamiliar environments. This knowledge will shed light on the causes of individual differences in spatial ability, and will aid in the development of freely moving robotic systems. The second line of experiments will investigate the causes of associative priming. When people retrieve information from memory, performance is often affected by previous retrieval operations or by the context in which the retrieval takes place. In the lexical decision task, for example, one must decide whether a string of letters is a word or a nonword (e.g., blit). It has been widely documented that lexical decisions on a word are faster and more accurate when the word is preceded by an associated word (e.g., hospital-doctor) than when the word is preceded by an unassociated word (e.g., library-doctor). This facilitation is called "priming," and it occurs in nearly all tasks that require memory retrieval. The goal of this line of research is to test various theories of associative priming. The ubiquity of priming indicates that it is caused by a fundamental mechanism of memory retrieval. Thus, an understanding of the causes of priming will provide important new insights into basic properties of human memory. ***
