EFFECTS OF WORKING MEMORY DEMAND ON PERFORMANCE AND MENTAL STRESS DURING THE STROOP TASK Harshad Chandrakant Petkar A thesis in the Department of Concordia Institute for Information Systems Engineering Presented in Partial Fulfillment of the Requirements for the Degree of Master in Applied Science (Quality Systems Engineering) at Concordia University Montreal, Quebec, Canada August 2011 © Harshad. C. Petkar 2011 CONCORDIA UNIVERSITY School of Graduate Studies This is to certify that the thesis prepared By: HarshadChandrakantPetkar Entitled: Effects of working memory demand on performance and mental stress during the Stroop task. This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Applied Science (Quality Systems Engineering) complies with the regulations of this University and meets the accepted standards with respect to originality and quality. Signed by the final examining committee: Dr. Z. Tian Chair Dr. G. J. Gouw Examiner Dr. C. Wang Examiner Dr. Y. Zeng Supervisor Approved by Director Concordia Institute for Information Systems Engineering 20 Dr. R.A.L. Drew, Dean Faculty of Engineering and Computer Science ii Abstract EFFECTS OF WORKING MEMORY DEMAND ON PERFORMANCE AND MENTAL STRESS DURING THE STROOP TASK Harshad Chandrakant Petkar Demands on working memory are associated with mental stress, but little is known about the underlying connection between the two. The primary purpose of this study was to quantify individual mental stress, and to monitor heart rate variability (HRV) during high and low working memory (WM) demands influenced by Stroop interference. Another aim was to quantify the performance and response time during the Stroop task and observe their trends during high and low (WM) demands. Finally, the third goal of this thesis was to predict the relationship between mental stress and performance. To this end heart rate was recorded both at rest and while performing the Stroop task. High and low WM demands were obtained by increasing the level of Stroop interference. The response time and performance were calculated for each difficulty level of the Stroop task, as well as during high and low WM demand. The power spectral components HF, LF, LF/HF and the time domain Mean R-R (S), Mean HR (1/min), were used as the components of HRV in the analysis. The results indicated that all the components of HRV examined were sensitive to WM demands. The HF and Mean R-R (S) components decreased with an increase in WM demands from the baseline values. The Mean HR (1/min), LF and the LF/HF ratio increased with increase in demands. Overall, the results indicated a reduction in HRV when higher order cognitive tasks were performed. The response time increased with WM demands. The performance in the Stroop task was decreased with an increase in WM demands. The results also indicated that an increase in WM demand correlates with an increase in an individual‟s stress level, and a decrease in performance level. iii The present thesis contributes to the ongoing analysis of human computer interaction in the laboratory environment, and its effects on the autonomic nervous system. It is recommended that future research be conducted at the workplace to better understand the relationship between human computer interaction and mental stress levels. iv Acknowledgements I would like to express my sincere gratitude to supervisor Dr. Yong Zeng, for his invaluable support and guidance throughout the course of this research and in writing this thesis. Timely help provided by the library and IT a help-desk personnel is also much appreciated. I am grateful to all my colleagues in the Design Lab for their co-operation during the course of this work. I would like to thank Ms. Thanh An Nguyen for her help in designing the Stroop test. v Dedicated To My Father and My Family vi Contents List of Figures ................................................................................................................................ ix 1. Introduction ................................................................................................................................. 1 1.1 Purpose and Motivation ........................................................................................................ 2 1.2 Objectives and Scope ............................................................................................................ 5 1.3 Thesis Outline ....................................................................................................................... 7 2. Background ................................................................................................................................. 9 2.1 Heart Rate Variability ............................................................................................................ 9 2.2 The Human Heart and QRS complex. ................................................................................. 12 2.3 The Stroop Test ................................................................................................................... 14 2.4 Mental Stress ....................................................................................................................... 15 2.5 Working Memory ................................................................................................................ 16 3. Literature Review...................................................................................................................... 19 3.1 The Stroop Test ................................................................................................................... 19 3.1.1 The Stroop Test and Working Memory ........................................................................ 19 3.1.2 The Stroop test and HRV .............................................................................................. 21 3.1.3 Stroop test and Performance ......................................................................................... 21 3.1.4 The Stroop test and other physiological parameters ..................................................... 22 3.1.5 The Stroop test and Mental stress ................................................................................. 22 3.2 Mental stress ........................................................................................................................ 23 3.2.1 Mental Stress and HRV ................................................................................................ 23 3.2.2 Mental Stress and WM demands .................................................................................. 25 3.2.3 Mental Stress and Performance .................................................................................... 25 4. Experimental Methods and HRV Data Analysis ....................................................................... 28 4.1 The Stroop Test ................................................................................................................... 28 4.1.1 Design of the Stroop Experiment ................................................................................. 32 4.1.2 Performance from the Stroop test ................................................................................. 33 4.2 Experimental setup and procedure ...................................................................................... 34 vii 4.2.1 Subjects ......................................................................................................................... 34 4.2.2 Sequence of Procedures ................................................................................................ 35 4.2.3 Experimental Apparatus ............................................................................................... 38 4.3 Data Processing: Data collection and segmentation ........................................................... 39 4.4 Analysis ............................................................................................................................... 41 4.4.1 Heart Rate Analysis Software ....................................................................................... 41 4.4.2 Time Domain Analysis ................................................................................................. 41 4.4.3 Frequency domain methods .......................................................................................... 42 5. Results and Discussions ............................................................................................................ 43 5.1 Results ................................................................................................................................. 43 5. 2 Discussion .......................................................................................................................... 58 6. Conclusion ................................................................................................................................ 64 6.1 Conclusions ......................................................................................................................... 64 6.2 Contributions ....................................................................................................................... 66 6.3 Future Work ......................................................................................................................... 67 Bibliography ................................................................................................................................