DRIVING, EYE-TRACKING AND VISUAL ENTROPY: EXPLORATION OF AGE AND TASK EFFECTS By Jess Gilland B.S., University of South Dakota, 2002 M.A., University of South Dakota, 2004 A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Department of Psychology The University of South Dakota May, 2008 Driving, Eye-tracking and Visual Entropy 2 The members of the Committee appointed to examine the Dissertation of Jess Gilland find it satisfactory and recommend that it be accepted ___________________________ Chairperson - Frank Schieber, Ph. D. ___________________________ Jan Berkhout, Ph. D. ___________________________ Thomas Langworthy, Ph. D. ___________________________ Doug Peterson, Ph. D. ___________________________ XT (Xiao-Tian) Wang 王晓田, Ph.D. Driving, Eye-tracking and Visual Entropy 3 Abstract Most driving-related eye-movement research completed before this present study has relied upon qualitative techniques to evaluate questions. These techniques primarily consist of descriptive statistics on distributional data. This is adequate for a single study, but can not be reliably compared to the results of another study having dissimilar conditions. This has led to a need for the development and testing of a new measurement technique that produces quantitative results that are scaleable across differing situations. The quantitative metric of entropy – derived from information theory – has been adapted toward this purpose. Visual entropy values were calculated from the eye movements of 28 young (M = 24, SD = 5.3 yrs) and 14 older (M = 75, SD = 5.6 yrs) participants who drove an instrumented vehicle along a predefined route while engaged in several functionally different cognitive tasks. Driver age and subsidiary task type (none, verbal, visual-spatial) were systematically varied in order to assess the sensitivity of the entropy metric to discriminate behaviors generated across these situational factors. Resulting entropy values were directly compared to several more common visual metrics such as pupil size, saccadic amplitude, and fixation dwell time. In all metrics, effects were most discernible in the visual-spatial condition which was further exacerbated in the older driver group. The finding that a visual attention task inhibited a visual scanning behavior the most supports Wickens’ multiple resource theory. The finding that older individuals were the most affected in all cases supports the idea that older individuals may have diminished visual-cognitive resources available during driving compared to their younger counterparts. Upon comparison of the different visual metrics it was found that the entropy metric proved to be more sensitive to attentional demands than all alternative visual metrics assessed (e.g. pupil size, dwell times, and saccadic amplitudes). The findings of this study strongly suggest that global measures of eye movement behavior captured by the entropy metric are useful for understanding the correlation between normal adult aging and task–induced cognitive demands within the context of real-world driving. Driving, Eye-tracking and Visual Entropy 4 Acknowledgments Many people donated vast amounts of time and support during this project. I would like to give thanks to these individuals: • I would like to thank Dr. Frank Schieber. Frank’s advice was invaluable during idea development, protocol implementation, and writing evaluation. Without his expertise, this project would not have progressed as efficiently as it did. • I would like to thank the members of my committee for taking time out of their busy schedules to oversee the project throughout the years. Dr. XT Wang Dr. Doug Peterson Dr. Jan Berkhout Dr. Thomas Langworthy • I would like to thank my wife Rebecca and two boys (Zander & Gavin) for their constant support throughout this project. I know it took longer than anticipated, but everything always works out in the end. Driving, Eye-tracking and Visual Entropy 5 Table of Contents List of Figures .................................................................................................................................................7 List of Tables...................................................................................................................................................9 Chapter 1 1.0 Review of Eye tracking literature............................................................................................................10 1.1 Eye-Tracking Instrumentation............................................................................................................10 1.2 Important Terminology.......................................................................................................................13 1.3 Driving Related Eye Tracking Studies ...............................................................................................19 1.3.1 Straight Road Driving.................................................................................................................21 1.3.2 Driving on Curves.......................................................................................................................25 1.3.3 Driver Experience (Novice versus Expert) .................................................................................32 1.3.4 Challenging Visual Conditions...................................................................................................34 1.3.4.1 Driving in the Rain..............................................................................................................34 1.3.4.2 Reading Signs at Night........................................................................................................36 1.3.4.3 Visually Cluttered (complex) Backgrounds........................................................................38 1.4 Role of Head Movements ...................................................................................................................40 1.5 Fatigue Effects....................................................................................................................................41 1.6 Driving Speed Effects.........................................................................................................................42 1.7 Age Effects .........................................................................................................................................43 1.8 Mental Workload and Driver's Eye Movements.................................................................................50 1.8.1 Loading Tasks.............................................................................................................................53 1.8.1.1 Spatial imagery Tasks .........................................................................................................53 1.8.1.2 Verbal Loading Tasks .........................................................................................................56 1.8.1.2.1 Mental Arithmetic .......................................................................................................56 1.8.1.2.2 N-Back Task................................................................................................................57 1.9 Additional Sources of Information .....................................................................................................59 1.10 Conclusions from the Review of the Eye Tracking Literature .........................................................59 Chapter 2 2.0 Quantitative Metric of Driver Eye Movement Behavior.........................................................................60 2.1 Spectral Analysis ................................................................................................................................60 2.2 Entropy as a Metric for Quantifying System Complexity ..................................................................61 2.2.1 Example #1 .................................................................................................................................62 2.2.2 Example #2 .................................................................................................................................63 2.2.3 Example #3 .................................................................................................................................65 2.3 Development of an Information Theory Metric for Quantifying the Complexity of Driver Eye Movement Behavior ............................................................................................................................70 2.3.1 Visual Entropy............................................................................................................................70 2.3.2 Markov Chain Modeling.............................................................................................................75 2.3.2.1 Demonstration of a Markov Model Calculation..................................................................78 2.4 Experimental Objectives and Research Hypotheses...........................................................................85 2.4.1 Hypotheses..................................................................................................................................87 2.4.1.1 Hypothesis #1 General Workload Effect.............................................................................87 2.4.1.2 Hypothesis #2 Workload by Modality Effect......................................................................87