The Relationship between Heart Rate Variability, Lay Theories of Self-Regulation, and Ego-Depletion: Evidence of Psychophysiological Pathways of Self-Regulation THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Arts in the Graduate School of The Ohio State University By DeWayne P. Williams Graduate Program in Psychology The Ohio State University 2014 Master's Examination Committee: Dr. Julian F. Thayer, Advisor Dr. Baldwin M. Way Dr. Kentaro Fujita Dr. Michael Vasey Copyrighted by DeWayne P. Williams 2014 Abstract Self-regulation (SR) is defined as the process by which people adopt and manage various goals and standards for their thoughts, feelings, and behavior, and then ensure that these goals and standards are met. Strong evidence shows that SR is a limited resource that when depleted, the individual experiences ego-depletion, a state where SR is operating at less than full capacity. However, to date, research has not examined the association between ego-depletion and physiological indices of SR capacity. The characteristic variability in the time series of heartbeats, or heart rate variability (HRV), has been considered a biomarker of SR capacity. One study found that individuals with high HRV did not experience task fatigue – a concept related to ego-depletion. Recent investigations also show that an individuals’ lay theories of SR predict ego-depletion, such that those who think that SR is a limited resource experience ego-depletion, while those who think SR in an unlimited resource do not differ in performance. Drawing on these studies, the present investigation attempts to replicate and extend previous findings. It was hypothesized that only those with low resting HRV will experience depletion. Moreover, the present investigation was designed to examine the direct relationship between lay theories of SR and HRV. Using an electrocardiogram (EKG), baseline-resting period HRV data were collected in 61 (42 White, 42 Women) participants that later completed a set of questionnaires, a depletion manipulation task, the Stroop task, and a second set of ii questionnaires. Lay theories of SR were assessed using the Implicit Theories of Willpower Scale (ITWS). Participants were randomly assigned to a depletion or non- depletion group: in the depletion manipulation, participants completed a task that required SR, presumably, depleting resources for later use. In contrast, those in the non- depletion manipulation completed a task that did not require SR. All participants then completed the Stroop task. Accuracy on the Stroop task was used to assess the degree of depletion between conditions and at varying levels of ITWS scores and baseline HRV. In line with previous studies, individuals in the depletion condition performed worse on the task than those in the non-depletion condition. Interestingly, this effect was independently moderated by both resting HRV and lay theories of SR. Individuals with low resting HRV or who think SR is limited experienced ego-depletion, where their respective counterparts did not show similar patterns. Additionally, analyses revealed a strong relationship between resting HRV and ITWS scores such that those with higher resting HRV were more likely to have unlimited theories of SR. These observations have important implications – throughout daily life, individuals are often faced with situations that require repeated SR behaviors. The present study suggests that having low HRV and/or holding limited-theories of SR may undermine successful prolonged SR. Limitations, implications, and future directions are discussed. iii This thesis is dedicated to Linderek Dorman. Rest in peace my friend. iv Acknowledgments I would like to thank my advisors Dr. Julian Thayer and Dr. Baldwin Way for their continued and unwavering support, guidance, and wisdom provided throughout this process. I also thank Dr. Kentaro Fujita for his unwavering diligence, support, and wisdom he provided on this project. Additionally, I would like to thank Dr. Julian Koenig for his remarkable support and commitment. I also would like to thank Cameron Rankin for his dedication and time devoted to this project. I would like to thank Dr. Mike Vasey for agreeing to serve on my committee and providing feedback on this project. Finally, I thank Lassiter Speller, Dr. LaBarron Hill, and Dr. John Sollers III for their continued support and mentorship. I would also like to thank my cohort for their invaluable time and effort in reading and listening to many revisions of this project. To my fellow colleagues in the Emotions and Quantitative Psychophysiology lab and Social Psychology Department, thank you for your helpful and thoughtful feedback on this project. Last but certainly not least, I would like to thank my love (Lauren Miller), mother (Patricia Williams), father (Terrence Williams), sister (Jazmin Williams), and daughter (Mariyah Williams) for their continued support, understanding, and unconditional love throughout my endeavors. v Vita 2006................................................................Twinsburg High School 2011................................................................B.A. Psychology, The Ohio State University 2012 to present ..............................................Graduate Research Assistant, Department of Psychology, The Ohio State University Publications Williams, D.P., Jarczok, M.N, Ellis R.,Thayer, J.F., Hillecke, T.K., Koenig. J., (in press). A Half-Year Follow-Up on the Test Retest Reliability of the Cold Pressor Task as a Measure of Pain Tolerance and Threshold. Pain Practice. Bhatt, R.,Williams, D.P., Kessier, M., Hillecke, T.K., Thayer, J.F., Koenig, J., (in press).The Dark Side of the Moon: Music may Reduce Pain but White Noise may Increase it! Music and Medicine. Hill, L. K., Hu., D. D., Williams, D. P., Sofletea, G. M., Cochran, J., Sollers 3rd, J. J. & Thayer, J. F. (2010). Effects of Autonomic Innervation of the Heart as a Function of Effector Tissue. Biomedical Sciences Instrumentation, 46, 202-207. Fields of Study Major Field: Psychology vi Table of Contents Abstract ............................................................................................................................... ii Dedication………………………………………………………………………………..iv Acknowledgments............................................................................................................... v Vita ..................................................................................................................................... vi List of Tables ................................................................................................................... viii List of Figures .................................................................................................................... ix Chapter 1: Introduction ...................................................................................................... 1 Chapter 2: Materials and Methods .................................................................................... 15 Chapter 3: Results………………………………………………………………………..24 Chapter 4: Discussion…………………………………………………………………....27 References ..................................................................................................... ……………34 Appendix A: Tables ......................................................................................................... .40 Appendix B: Figures…………………………………………………………………......44 Appendix C: Implicit Theories of Willpower Scale……………………………………..59 vii List of Tables Table 1. Sample Demographics ........................................................................................ 40 Table 2. Baseline Characteristics by Depletion Group Manipulation ............................. 41 Table 3. High and Low HRV Group Comparisons on Baseline Variables .....………….42 Table 4 Correlation Matrix of Variables….……………………………………………...43 viii List of Figures Figure 1. Conceptual Diagram of Self-Regulation ........................................................... 44 Figure 2. Conceptual Representation of Model 1 in PROCESS ....................................... 45 Figure 3. Statistical Representation of Model 1 in PROCESS ......................................... 46 Figure 4. Conceptual Representation of Model 2 in PROCESS ....................................... 47 Figure 5. Statistical Representation of Model 2 in PROCESS ......................................... 48 Figure 6. Scatter Plot of Resting HRV and Lay Theories of SR ...................................... 49 Figure 7. Conceptual Diagram of Moderation Test between Lay Theories of SR, Depletion, and Performance.............................................................................................. 50 Figure 8. Statistical Diagram of Moderation Test between Lay Theories of SR, Depletion, and Performance ............................................................................................................... 51 Figure 9. Interaction between Lay Theories of SR and Depletion on Performance ......... 52 Figure 10. Conceptual Diagram of Moderation Test between Resting HRV, Depletion, and Performance ............................................................................................................... 53 Figure 11. Statistical Diagram of Moderation Test between Resting HRV, Depletion, and Performance ...................................................................................................................... 54 Figure 12. Interaction between Resting HRV, Depletion,