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Analysis of Eye Movement Data Frank M. Marchak, Ph.D. Veridical Research and Design Corporation www.vradc.com PowerPoint Presentation
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Analysis of Eye Movement Data Frank M. Marchak, Ph.D. Veridical Research and Design Corporation www.vradc.com

Analysis of Eye Movement Data Frank M. Marchak, Ph.D. Veridical Research and Design Corporation www.vradc.com

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Analysis of Eye Movement Data Frank M. Marchak, Ph.D. Veridical Research and Design Corporation www.vradc.com

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  1. Analysis of Eye Movement Data Frank M. Marchak, Ph.D.Veridical Research and Design Corporationwww.vradc.com

  2. Analysis of Eye Movement DataBasic Measurement Units • Fixations • Saccades • Blinks

  3. Basic Measurement UnitsFixations • Relatively stable eye-in-head position: • Spatial dispersion : < 2° • Minimal duration : 100 – 200 msec • Threshold velocity : < 15 – 100° /msec www.uxmatters.com/mt/archives/2006/01/images/4_flickr_cumulative.jpg

  4. FixationsCalculation Methods* • Velocity-based • Based on point-to-point velocities- (threshold : 20°/sec) • Fixations (< 100° /sec) • Saccades (> 300° /sec) • Velocity Threshold Identification • Approximated from angular velocity threshold distance from stimulus is known (20°/sec – Sen & Megaw, 1984) • Dispersion-based • Based on groups of consecutive points within a maximum separation • Movingwindow spans minimum number of points based on duration threshold and sampling frequency • Checks dispersion of points in window by summing max and min x and y values * Salvucci & Goldberg, 2000

  5. FixationsCalculation Methods* (cont.) • Area-of-Interest (AOI) • Identifies only fixations that occur only within specific target areas • Uses duration threshold to distinguish fixations from passing saccades Comparison * Salvucci & Goldberg, 2000

  6. Basic Measurement UnitsSaccades • Involuntary, abrupt, rapid, small movements or jerks of both eyes simultaneously in changing the point of fixation • Duration: 30 – 120 msec • Amplitude : 400 - 600°/sec • Latency : 100 – 30 msec • Refractory period : 100 – 300 msec

  7. Basic Measurement UnitsMean Fixation Durations and Saccade Lengths Rayner & Castelhano, 2007

  8. Analysis of Eye Movement DataTypes of Analyses* • Measures of Processing • Measures of Search • Measures of Scanpaths * Goldberg & Kotval, 1999

  9. Types of AnalysesMeasures of Processing • Number of Fixations • Location of Fixations • Fixation Duration • Cumulative Fixation Time • Cluster Analysis (AOI)

  10. Types of AnalysesMeasures of Search • Number of Saccades • Saccade Amplitude • Saccade Velocity • Scanpath Length • Scanpath Sequence • Scanpath Duration

  11. Types of AnalysesScanpaths • When a particular visual pattern is viewed, a particular sequence of eye movements is executed, and furthermore that this sequence is very important in accessing the visual memory for this pattern • Noton and Stark, 1971 • Theory disputed, but evidencethat viewers attend to informativedetails http://eyetracking.com.ua/frmtext/10.jpg

  12. ScanpathsQuantification – Markov Measures Random

  13. ScanpathsQuantification – Markov Measures Constrained

  14. ScanpathsQuantification – Levenshtein Distance • Metric for measuring the amount of difference between two sequences • Defined as the minimum number of edits needed to transform one string into the other, with the allowable edit operations being insertion, deletion, or substitution of a single character Josephson and Holmes, 2002 en.wikipedia.org/wiki/Levenshtein_distance

  15. Analysis of Eye Movement DataApplications of Measures • Reading • Visual Search • Scene Perception

  16. Measures of ProcessingExample • Number of fixations • Σx + Σ x + Σx + Σx = 11 • Number of regions sampled • 1 + 1 + 1 + 1 = 4 • First return fixation • * • Proportion of fixations to left side of image • 6/11 = .55 • First-order Markov measures • p(x x) • Second-order Markov measures • p(x x x) * x x x x x x x x x x x

  17. Basic Measurement UnitsBlinks • Rapid bilateral eyelid closure and co-occurring eye movement • Blink types and initiators* * Smit, 2008

  18. Applications of MeasuresReading • Variables • First Fixation Duration • Single Fixation Duration • Gaze Duration • Total Fixation Duration • Go-Past Time • Skipping • Regressions (in and out) Rayner & Castelhano, 2007

  19. ReadingCharacteristics • Character spaces used rather than visual angle • Global measures influenced by text properties • Saccade size • Fixation duration • Regression to previously read material(10-15%) • Local effects on processing target words • First fixation duration • Single fixation duration • Gaze duration (sum of all fixations on word)

  20. Applications of MeasuresVisual Search • Variables • Number of Saccades • Saccade Amplitude • Saccade Velocity • Scanpath Length • Scanpath Sequence • Scanpath Duration Rayner & Castelhano, 2007

  21. Applications of MeasuresScene Perception • Variables • Number of Fixations • First Return Fixation • Number of Regions • 1st order Markov • 2nd order Markov Rayner & Castelhano, 2007

  22. Scene PerceptionScene Manipulation • 60 Stimuli • 15 Addition/15 Subtraction • 15 Left/right shift • 15 Feature change • Detail • Color • Object