The Pennsylvania State University The Graduate School Department of Psychology ADULT HUMAN CORTICAL RESPONSES TUNED TO FIGURES DEFINED BY TEMPORAL MODULATIONS OF MOTION CONTRAST: AN ELECTROPHYSIOLOGICAL INVESTIGATION OF CORTICAL FUNCTION A Thesis in Psychology

Motion differences contribute to the segregation of a figure from its background. While some important work has addressed the role of motion in figure processing, many questions remain as to the cortical structures involved and their particular activation properties. In the research described here, I measured steady-state visual evoked potential responses to moving dot displays in which figure regions emerged from and disappeared into the background at a specific temporal frequency (1.2 Hz, F1), based on differences of dot direction, speed, motion coherence, dot lifetime, and dot density settings. Experiment 1 compares responses to displays of qualitatively different figure/ground contrast relationships. Experiment 2 explores evoked responses to quantitatively controlled magnitudes of contrast, revealing cortical tuning patterns to figure/ground differences in direction, speed, and coherence of motion. For each of the condition groups, response tuning likely reflects two functional components of motion-defined form processing: motion contrast magnitude and a magnitude-invariant response (possibly related to figural grouping). Experiments 3 5 validate and expand upon the assumptions of Experiment 2. Experiment 3 manipulates dot lifetime settings to examine how the response to motion-defined form displays will modulate as local-level motion vectors are increased or decreased. Experiment 4 changes dot density settings to investigate the dependence of the evoked responses on locallevel motion contrast information, or edges. Experiment 5 uses a 128-electrode montage to better isolate the location of the tuned responses along the scalp. iv TABLE OF CONTENTS LIST OF FIGURES ................................................................................................................. .v Chapter 1 Motion Contrast as a Cue for Figure Segregation ................................................. ..1 Chapter 2 Experiment 1: Preliminaries .................................................................................. ..12 Chapter 3 Experiment 2: Tuned Responses to Motion-Defined Figures................................ ..19 Chapter 4 Experiment 3: Timing Properties of Responses to Motion-Defined Figures ........ ..31 Chapter 5 Experiment 4: Spatial Thresholds of Responses to Motion-Defined Figures........ ..37 Chapter 6 Experiment 5: Motion-Defined Figure Tuning & High Density VEP................... ..41 Chapter 7 General Discussion............................................................................49 References...................................................................................................56