Divide and Conquer: How Perceived Reference Axes Help Maintain Memory for Locations

University Of Iowa, Iowa City IA

Investigators

Abstract

To interact successfully in the environment, people must remember the locations of important objects accurately enough to find these objects when they are no longer in view. Otherwise, keys, shoes, and hats would be lost forever in the clutter of the typical home or office. The majority of research investigating the characteristics of location memory has focused on WHAT people represent in memory. For instance, do people represent that a set of keys is two inches to the left of a computer, or do they represent that the keys are one arms-length away? Although what is represented is a fundamental question, this research will examine a different, but equally important question: HOW do people maintain location information in memory? This question is timely because recent studies with non-human primates have identified several brain regions that contribute to the maintenance of location information in memory. Thus, there is a growing understanding of how the brain keeps location information active in memory. Nevertheless, few studies with humans have interfaced with this emerging knowledge base. This research will establish a link between behavioral studies of how humans remember locations and the literature on brain function. Central to this research is how people use perceptual cues from second-to-second to help maintain information in memory. Evidence from a variety of studies suggests that people rely on visible reference axes, e.g., the edges of a table, the edges of a computer screen, to help them remember the locations of target objects. Use of such perceptual cues can help keep remembered information in the right ballpark (the keys are near the left edge of the table and not over by the computer). Nevertheless, there is a cost, in that memory is systematically distorted near reference axes. Specifically, when people are asked to reproduce the location of a hidden object, they exaggerate the distance between the reference axis and the actual location of the object. These memory errors are particularly informative because they increase in magnitude as memory delays increase. Thus, errors away from reference axes provide a window into the second-to-second processes that serve to maintain location information in memory. This research will test a mathematical model of these maintenance processes, a model that specifies how a network of neurons can give rise to the types of memory errors humans make. Nine experiments will test this model of how location memory works. The first five experiments will test specific predictions of the model. These experiments will establish whether people make the particular types of memory errors predicted by the model, and whether these errors do, in fact, result from the use of reference axes. The final four experiments will examine the generality of the model to novel situations. For instance, do adults make the same types of memory errors when they are forced to attend to non-target locations during a memory delay? When completed, this project will provide the first formal model of the processes that maintain location information in memory over short-term delays. This model and the associated empirical data may have broad implications. For instance, the model will provide insights into what cues most effectively maintain information in memory. This could lead to an informed re-structuring of the environment for people who have difficulty maintaining information in working memory, such as elderly participants and patients suffering from Alzheimer's Disease. The model could also predict what patterns of error are most likely when people are unskilled (e.g., early in development), and what processes might be most severely disrupted under conditions of stress or strain (e.g., sleep deprivation, impaired visual processing, brain injury).