Encoding Strategies, Hemifields, and Shape Complexity, Oh My! An Investigation of Methods to Improve Memory Performance

Laura R. Rabbitt

Advisor: Matthew Peterson, Department of Psychology

Committee Members: William Helton

Online Location, Online
April 12, 2024, 10:00 AM to 12:00 PM

Abstract:

Working memory (WM) is a form of temporary memory where information is stored for brief periods of time and is manipulated to support on-going cognitive tasks, such as counting or performing mathematical computations. WM is limited by the number of items that may be maintained, which is referred to as capacity. In order to overcome limits in WM capacity, researchers have investigated many methods to overcome these limitations and improve performance. The present research conducted a series of experiments to understand the effects of encoding strategies on WM capacity measures, and examined the potential for multiple strategies to synergize to improve WM performance. In this series of experiments, encoding strategies came in the form of task instructions. Participants were either provided instructions to remember the locations of items (which served as the as the control condition) or were provided instructions to remember the locations of items by forming patterns between the items, like a constellation (referred to as constellation instructions and served as the experimental condition). Study 1 investigated the effects of encoding strategies on spatial WM performance and if it could be indexed by the same neurophysiological markers of visual WM capacity. The results of Study 1 found that spatial WM could be indexed by neurophysiological markers of visual WM and for participants in the constellation condition, the neurophysiological marker supported the notion that participants formed connections between locations. Additionally, there were differences in the duration of the neurophysiological across instruction conditions where participants in the constellation condition had prolonged activity than participants in the control condition. Study 1 did not see effects in capacity performance but did see differences reflected in neurophysiological markers of spatial WM, providing evidence that participants were indeed forming a constellation when instructed to do so. Study 2 investigated the effects of encoding strategies with task instructions combined with the effects of stimulus organization to determine if there were additive effects of these two strategies. Stimulus organization was varied by presenting items within a single visual hemifield, thus utilizing a single hemisphere of the brain, or presented items across both visual hemifields, utilizing both hemispheres of the brain. The results of Study 2 found that participants recalled more items when items when stimuli were arranged bilaterally (across visual hemifields) than unilaterally (within a visual hemifield). There was not an effect of task instruction on capacity measures; however, there were differences observed in reaction time measures. Participants in the constellation condition responded faster than participants in the control condition. While Study 2 found different effects of stimulus organization and encoding strategies on spatial WM measures, it is not possible to understand the mechanisms behind these effects. To further investigate the role of spatial organization of stimulus arrays and encoding strategies, Study 3 introduced an additional factor of stimulus complexity. The goal of this manipulation was to determine if WM capacity improvements were due to an increase in the amount of resources available (i.e., each hemisphere has its own reserve of resources) or if WM capacity improvements were due to an increased number of “slots” available to encode and store items (i.e., each hemisphere has its own number of slots). Stimulus complexity was varied by types of shapes: complex shapes in the form of irregular polygons or simple shapes in the form of squares. If memory capacity did not vary across stimulus complexity, it would support the notion that there are more slots available; however, if memory capacity did vary with stimulus complexity it would support the notion there are more resources available. The results of Study 3 indicated partial support for greater resource availability as there were differences in performance with shape complexity; however, these results were only seen in the constellation condition. Overall, these studies find that there are improvements in spatial WM performance when participants are provided encoding strategies which can be further improved when information is organized in a way that leverages both hemispheres of the brain.