Human Preferences for Symmetry: Subjective Experience, Cognitive Conflict and Cortical Brain Activity

This study examines the links between human perceptions, cognitive biases and neural processing of symmetrical stimuli. While preferences for symmetry have largely been examined in the context of disorders such as obsessive-compulsive disorder and autism spectrum disorders, we examine various these phenomena in non-clinical subjects and suggest that such preferences are distributed throughout the typical population as part of our cognitive and neural architecture. In Experiment 1, 82 young adults reported on the frequency of their obsessive-compulsive spectrum behaviors. Subjects also performed an emotional Stroop or variant of an Implicit Association Task (the OC-CIT) developed to assess cognitive biases for symmetry. Data not only reveal that subjects evidence a cognitive conflict when asked to match images of positive affect with asymmetrical stimuli, and disgust with symmetry, but also that their slowed reaction times when asked to do so were predicted by reports of OC behavior, particularly checking behavior. In Experiment 2, 26 participants were administered an oddball Event-Related Potential task specifically designed to assess sensitivity to symmetry as well as the OC-CIT. These data revealed that reaction times on the OC-CIT were strongly predicted by frontal electrode sites indicating faster processing of an asymmetrical stimulus (unparallel lines) relative to a symmetrical stimulus (parallel lines). The results point to an overall cognitive bias linking disgust with asymmetry and suggest that such cognitive biases are reflected in neural responses to symmetrical/asymmetrical stimuli.

Investigation of the Design of a Bistable Micro-Chemical-Mechanical Device Utilizing Lateral Buckling

The Gracias Laboratory at Johns Hopkins University has developed microgrippers which utilize chemically-actuated joints to be used in micro-surgery. These grippers, however, take up to thirty minutes to close fully when activated biochemicals in the human body. This is very problematic and could limit the use of the devices in surgery. It is the goal of this research to develop a gripper that uses theGracias Laboratory's existing joints in conjunction with mechanical components to decrease the closing time. The purpose of including the mechanical components is to induce a state of instability at which time a small perturbation would cause the joint to close fully.The main concept of the research was to use the lateral buckling of a triangular gripper geometry and use a toggle mechanism to decrease the closure time of the device. This would create a snap-action device mimicking the quick closure of a Venus flytrap. All developed geometries were tested using finite element analysis to determine ifloading conditions produced the desired buckled shape. This research examines lateral buckling on the micro-scale and the possibility ofusing this phenomenon in a micro-gripper. Although a final geometry with the required deformed shaped was not found, this document contains suggestions for future geometries that may produce the correct deformed shape. It was determined through this work that in order to obtain the desired deformed shape, polymeric sections need to be added to the geometry. This simplifies the analysis and allows the triangular structure to buckle in the appropriate way due to the added joints. Future work for this project will be completed by undergraduate students at Bucknell University. Fabrication and testing of devices will be done at Johns Hopkins University in the Gracias Laboratory.