Eye Tracking A Comprehensive Guide to Methods and Measures

Transcription

1 Eye Tracking A Comprehensive Guide to Methods and Measures Kenneth Holmqvist Humanities Laboratory Lund University Sweden Marcus Nyström Humanities Laboratory Lund University Sweden Richard Andersson Humanities Laboratory Lund University Sweden Richard Dewhurst Humanities Laboratory Lund University Sweden Halszka Jarodzka Centre for Learning Sciences and Technologies Heerlen the Netherlands Joost van de Weijer Humanities Laboratory Lund University Sweden OXFORD UNIVERSITY PRESS

2 Contents About the authors xix 1 Introduction The structure of this book Technical and methodological skills Events and representations Measures and their operational definitions How eye-movement measures are described in this book The target question and the summary box The name(s) The operational definitions Typical values and histograms Usage Terminology and style Material used in the book 5 I TECHNICAL AND METHODOLOGICAL SKILLS 2 Eye-tracker Hardware and its Properties A brief history of the competences around eye-trackers Manufacturers and customers Hands-on advice on how to choose infrastructure and hardware How to set up an eye-tracking laboratory Eye-tracking labs as physical spaces Types of laboratories and their infrastructure Measuring the movements of the eye The eye and its movements Binocular properties of eye movements Pupil and corneal reflection eye tracking Data quality Sampling frequency: what speed do you need? Accuracy and precision Eye-tracker latencies, temporal precision, and stimulus-synchronization latencies Filtering and denoising Active and passive gaze contingency Types of eye-trackers and the properties of their set-up The three types of video-based eye-trackers 51

3 X I CONTENTS Robustness Tracking range and headboxes Mono- versus binocular eye tracking The parallax error Data samples and the frames of reference Summary 64 From Vague Idea to Experimental Design The initial stage explorative pilots, fishing trips, operationalizations, and highway research The explorative pilot The fishing trip Theory-driven operationalizations Operationalization through traditions and paradigms What caused the effect? The need to understand what you are studying Correlation and causality: a matter of control What measures to select as dependent variables The task Stimulus scene, and the areas of interest Trials and their durations How to deal with participant variation Participant sample size Planning for statistical success Data exploration Data description Data analysis Data modelling Further statistical considerations Auxiliary data: planning Methodological triangulation of eye movement and auxiliary data Questionnaires and Likert scales Reaction time measures Galvanic skin response (GSR) Motion tracking Electroencephalography (EEG) Functional magnetic resonance imaging (fmri) Verbal data Summary 108 Data Recording Hands-on advice for data recording Building the experiment Stimulus preparation Physically building the recording environment 113

4 CONTENTS I Xi Pilot testing the experiment Participant recruitment and ethics Ethics toward participants Eye camera set-up Mascara Droopy eyelids and downward eyelashes Shadows and infrared reflections in glasses Bi-focal glasses Contact lenses Direct sunlight and other infrared sources The fourth Purkinje reflection Wet eyes due to tears or allergic reactions The retinal reflection (bright-pupil condition) Mirror orientation and dirty mirrors Calibration Points Geometry The calibration procedure Corner point difficulties and solutions Calibration validation Binocular and head-tracking calibration Calibration tricks with head-mounted systems Instructions and start of recording Auxiliary data: recording Non-interfering set-ups Interfering set-ups Verbal data Debriefing Preparations for data analysis Data quality Analysis software for eye-tracking data Summary 143 II DETECTING EVENTS AND BUILDING REPRESENTATIONS Estimating Oculomotor Events from Raw Data Samples The setting dialogues and the output Principles and algorithms for event detection Hands-on advice for event detection Challenging issues in event detection Choosing parameter settings Noise, artefacts, and data quality 161

5 xii I CONTENTS Glissades Sampling frequency Smooth pursuit Binocularity Algorithmic definitions Dispersion-based algorithms Velocity and acceleration algorithms Manual coding of events Blink detection Smooth pursuit detection Detecti on of noise and artefacts Detecti on of other events Summary: oculomotor events in eye-movement data Areas of Interest The AOI editor and your hypothesis Hands- on advice for using AOIs The basic AOI events The AOI hit The dwell The transition The return The AOI first skip The AOI total skip AOI-based representations of data Dwell maps The AOI strings Transition matrices Markov models AOIs over time Time and order Types of AOIs Whitespace Planes Dynamic AOIs Distributed AOIs Gridded AOIs Fuzzy AOIs Stimulus-inherent AOI orders Participant-specific AOI identities AOI identities across stimuli AOIs in the feature domain Challenging issues with AOIs

6 CONTENTS) Xiii Choosing and positioning AOIs Overlapping AOIs Deciding the size of an AOI Data samples or fixations and saccades? Dealing with inaccurate data Normalizing AOI measures to size, position, and content AOIs in gaze-overlaid videos Summary: events and representations from AOIs Attention Maps Scientific Tools or Fancy Visualizations? Heat map settings dialogues Principles and terminology Hands-on advice for using attention maps Challenging issues: interpreting and building attention maps Interpreting attention map visualizations How many fixations/participants? How attention maps are built Usage of attention maps other than for visualization Using attention maps to define AOIs Attention maps as image and data processing tools Using attention maps in measures Summary: attention map representations Scanpaths Theoretical Principles and Practical Application What is a scanpath? Hands-on advice for using scanpaths Usages of scanpath visualization Data quality checks Data analysis by visual inspection Exhibiting scanpaths in publications Scanpath events The backtrack The regression family of events The look-back and inhibition of return The look-ahead The local and global subscans Ambient versus focal fixations The sweep The reading and scanning events Scanpath representations Symbol sequences Vector sequences Attention map sequences Principles for scanpath comparison 273

7 xiv i CONTENTS Representation Simplification Sequence alignment Calculation Pairwise versus groupwise comparison Unresolved issues concerning scanpaths Relationships between scanpaths and cognitive processes Scanpath Theory Scanpath planning The average scanpath Comparing scanpaths Summary: scanpath events and representations Auxiliary Data: Events and Representations Event-based coalignment Alignment of eye-tracking events with auxiliary data Latencies between events in eye-tracking and auxiliary data Triangulating eye-movement data with verbal data Detecting events in verbal data: transcribing verbalizations and segmenting them into idea units Coding of verbal data units Representations, measures, and statistical considerations for verbal data Open issues: how to co-analyse eye-movement and verbal data Summary: events and representations with auxiliary data 296 III MEASURES 10 Movement Measures Movement direction measures Saccadic direction Glissadic direction Microsaccadic direction Smooth pursuit direction Scanpath direction Movement amplitude measures Saccadic amplitude Glissadic amplitude Microsaccadic amplitude Smooth pursuit length Scanpath length Blink amplitude Movement duration measures Saccadic duration 321

8 CONTENTS XV Scanpath duration Blink duration Movement velocity measures Saccadic velocity Smooth pursuit velocity Scanpath velocity and reading speed Pupil constriction and dilation velocity Movement acceleration measures Saccadic acceleration/deceleration Skewness of the saccadic velocity profile Smooth pursuit acceleration Saccadic jerk Movement shape measures Saccadic curvature Glissadic curvature Smooth pursuit: degree of smoothness Global to local scanpath ratio AOl order and transition measures Order of first AOl entries Transition matrix density Transition matrix entropy Number and proportion of specific subscans Unique AOIs Statistical analysis of a transition matrix Scanpath comparison measures Correlation between sequences Attention map sequence similarity The string edit distance Refined AOl sequence alignment measures Vector sequence alignment Position Measures Basic position measures Position Landing position in AOl Position dispersion measures Comparison of dispersion measures Standard deviation, variance, and RMS Range Nearest neighbour index The convex hull area Bivariate contour ellipse area (BCEA) Skewness of the Voronoi cell distribution 366

9 xvi I CONTENTS Coverage, and volume under an attention map Relative entropy and the Kullback-Leibler Distance (KLD) Average landing altitude Position similarity measures Euclidean distance Mannan similarity index The earth mover distance The attention map difference Average landing altitude The angle between dwell map vectors The correlation coefficient between two attention maps The Kullback-Leibler distance Position duration measures The inter-microsaccadic interval (IMSI) Fixation duration The skewness of the frequency distribution of fixation durations First fixation duration after onset of stimulus First fixation duration in an AOI, and also the second Dwell time Total dwell time First and second pass (dwell) times in an AOI Reading depth Pupil diameter Position data and confounding factors Participant brainware and substances Participant cultural background Participant experience and anticipation Communication, imagination, and problem solving Central bias The stimulus Numerosity Measures Saccades: number, proportion, and rate Number of saccades Proportion of saccades Saccadic rate Glissadic proportion Microsaccadic rate Square-wave jerk rate Smooth pursuit rate Blink rate Fixations: number, proportion, and rate Number of fixations 412

10 CONTENTS I XVII Proportion of fixations Fixation rate Dwells: number, proportion, and rate Number of dwells (entries) in an area of interest Proportion of dwells to an area of interest Dwell rate Participant, area of interest, and trial proportion Participant looking and skipping proportions Proportion of areas of interest looked at Proportion of trials Transition number, proportion, and rate Number of transitions Number of returns to an area of interest Transition rate Number and rate of regressions, backtracks, look-backs, and look-aheads Number of regressions in and between areas of interest Number of regressions out of and into an area of interest Regression rate Number of backtracks Number of look-aheads Latency and Distance Measures Latency measures Saccadic latency Smooth pursuit latency Latency of the reflex blink Pupil dilation latency EFRPs eye fixation related potentials Entry time in AOI Thresholded entry time Latency of the proportion of participants over time Return time Eye-voice latencies Eye-hand span The eye-eye span (cross-recurrence analysis) Distances Eye-mouse distance Disparities Smooth pursuit gain Smooth pursuit phase Saccadic gain What are Eye-Movement Measures and How can they be Harnessed? Eye-movement measures: plentiful but poorly accessible 454

11 xviii [CONTENTS 14.2 Measure concepts and operationalizing them Proposed model of eye-tracking measures Classification of eye-movement measures How to construct even more measures Summary 468 References 469 Index 521