The removal of ocular artifact from the EEG

228 Pages·2011·3.51 MB·English

University of Wollongong
Research Online
University of Wollongong Thesis Collection University of Wollongong Thesis Collections
1999
The removal of ocular artifact from the EEG
Rodney J. Croft
University of Wollongong
Recommended Citation
Croft, Rodney J., The removal of ocular artifact from the EEG, Doctor of Philosophy thesis, University of Wollongong.Department of
Psychology, University of Wollongong, 1999. http://ro.uow.edu.au/theses/1693
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University of Wollongong
Candidate's Certificate
I certify that the thesis entitled "The Removal of Ocular Artifact
from the EEG", submitted for the degree of Doctor of Philosophy, is
the result of my own research, except where otherwise
acknowledged, and that this thesis (or any part of the same) has not
been submitted for a degree at any other university or institution.

Signe
Date....^.-.7:.B.^
The Removal of Ocular Artifact from the E EG
by
Rodney J. Croft, B.A., B.Sc.(Hons)
University of Wollongong
Thesis presented to
Department of Psychology,
University of Wollongong
for the degree of Ph.D., July 1999
2
CONTENTS
LIST OF TABLES 8
LIST OF FIGURES 10
ACKNOWLEDGEMENTS 15
STATEMENT 16
ABSTRACT 18
CHAPTER 1: Ocular artifact in the EEG 20
1.1 General Background 20
1.2 How is the eye-movement voltage generated? 22
1.2.1 Cornea-Retinal Dipole Movement 23
1.2.2 Retinal Dipole Movement. 23
1.2.3 Eyelid Movement 23
1.3 Typical patterning of the eye-movement voltages across
the scalp 24
1.4 How do we measure the eye-movements? 24
1.5 Methods for accounting for ocular artifacts 27
1.5.1 Recording with eyes closed 28
1.5.2 Experimental Control 28
1.5.3 EOG Rejection 29
1.5.4 EOG Correction 31
1.5.4.1 Early Analogue Techniques 32
1.5.4.2 Advanced Regression Techniques 33
1.6 The problem with EOG correction 34
CHAPTER 2: Towards a unified EOG correction theory 38
2.1 The Frequency Domain Approach 40
2.1.1 Arguments for treating different frequencies differently 41
2.1.2 Evaluation of these arguments 42
2.2 The calculation of separate Bs for blinks and other types of
eye- movement voltages? 45
2.2.1 Arguments for the distinction 47
2.2.2 Evaluation of these arguments 48
2.3 Does EOG magnitude significantly affect B? 50
2.4 Conclusions 55
CHAPTER 3: Determining if EOG magnitude affects B
estimates 56
3.1 Computer simulation data 56
3.1 1 Introduction 56
3.1.2 Method 57
3.1.2.1 Simulations 57
3.1.2.2 Statistical Methods 58
3.1.3 Results 59
3.1.4 Discussion 61
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3.2 Real data 63
3.2.1 Introduction 63
3.2.2 Method 64
3.2.2.1 Subjects 64
3.2.2.2 Data Acquisition 65
3.2.2.3 Procedure 65
3.2.2.4 Data Analysis 66
3.2.3 Results 66
3.2.4 Discussion 68
CHAPTER 4: Determining whether the relationship
between B and EOG magnitude is real or
artifactual in nature 72
4.1 Controlling for DC shifts in the EOG and EEG
channels 73
4.1.1 Introduction 73
4.1.2 Method 74
4.1.2.1 Subjects 74
4.1.2.2 Data Acquisition 74
4.1.2.3 Procedure 75
4.1.2.4 Data Manipulation 75
4.1.2.5 Statistical Analysis 75
4.1.3 Results 76
4.1.4 Discussion 78
4.2 Controlling for other forms of interference in the EOG and
EEG channels 79
4.2.1 Introduction 79
4.2.2 Method 81
4.2.2.1 Subjects 81
4.2.2.2 Data Acquisition 81
4.2.2.3 Procedure 81
4.2.2.4 Data Manipulation 81
4.2.2.5 Statistical Analysis 81
4.2.3 Results 82
4.2.4 Discussion 84
CHAPTER 5: How best to account for preexisting
interference in the EOG and EEG channels?... 87
5.1 Introduction 87
5.2 Forward Propagation (preexisting coherent interference) 88
5.2.1 Calibration Trials 88
5.2.2 Large Magnitude EOG 89
5.2.3 Modeling the EEG 90
5.2.4 A Priori Cut-Offs 92
5.2.5 Separation of ocular from other EOG voltages 92
5.2.6 Dipole Modeling 93
5.2.7 The Artifact-Aligned Average procedure 94
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5.3 D.C. Shifts (preexisting coherent interference) 94
5.3.1 Frequency Domain Approach/ Filtering 95
5.3.2 Subtraction. 95
5.3.3 The Aligned-Artifact Average Procedure 96
5.3.4 Other techniques 96
5.3.5 Conclusion 96
5.4 Other Sources (preexisting coherent interference) 97
5.5 Preexisting Incoherent Interference 97
5.6 Conclusion 98
CHAPTER 6: An empirical test of the AAA. 99
6.1 Introduction 99
6.2 Method 100
6.2.1 Simulations 100
6.2.2 Statistical Methods 101
6.2.2.1 Gratton-Style 101
6.2.2.1.1 Forward Propagation Condition. 101
6.2.2.1.2 Forward Propagation / Coherent Interference Condition.. 101
6.2.2.2 AAA Correction Method 102
6.2.2.2.1 Forward Propagation Condition. 102
6.2.2.2.2 Forward Propagation / Coherent Interference Condition. 102
6.2.2.3 General 102
6.3 Results 105
6.3.1 Forward Propagation Condition 105
6.3.2 Forward Propagation /Coherent Interference Condition 105
6.4 Discussion 106
CHAPTER 7: Issues pertinent to the AAA procedure:
comparing different calibration methods, and
determining the number of epochs required... 108
7.1 Introduction 108
7.2 Method 110
7.2.1 Subjects 110
7.2.2 Data Acquisition 110
7.2.3 Procedure Ill
7.2.3.1 Analysis One Ill
7.2.3.1.1 Data Manipulation. Ill
7.2.3.1.1.1 AAA Ill
7.2.3.1.1.2 NERP 112
7.2.3.1.2 Statistical Analysis 112
7.2.3.1.3 Results 112
7.2.3.2 Analysis Two 114
7.2.3.2.1 Data Manipulation 114
7.2.3.2.2 Statistical Analysis 114
7.2.3.2.3 Results 114
7.3 Discussion 1
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CHAPTER 8: Correcting blink data with saccade Bs 119
8.1 Introduction 119
8.2 Method 124
8.2.1 Subjects 124
8.2.2 Data Acquisition 124
8.2.3 Procedure 124
8.2.4 Data Manipulation 124
8.2.4.1 Eye calibration 124
8.2.4.2 Eye-Movement Data 125
8.2.4.3 Blink Data 126
8.2.4.4 Correction 127
8.2.5 Statistical Analysis 128
8.3 Results 129
8.4 Discussion 134
CHAPTER 9: The effect of the radial channel on eye-blink
correction 141
9.1 Introduction 141
9.2 Method 145
9.2.1 Subjects 145
9.2.2 Data Acquisition 145
9.2.3 Procedure 145
9.2.4 Data Manipulation 145
9.2.4.1 Eye Calibration 145
9.2.4.2 Eye-Movement Data 146
9.2.4.3 Blink Data 146
9.2.4.4 Correction 146
9.2.5 Statistical Analysis 147
9.3 Results 150
9.4 Discussion 150
CHAPTER 10: Issues relating to the type of regression 156
10.1 Introduction 156
10.1.1 Time points as data 156
10.1.2 Simultaneous multiple, multiple-stage, or hierarchical
regression?. jg
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10.2 Method 163
10.2.1 Analysis 1 163
10.2.1.1 Simulations 163
10.2.1.2 Data Manipulation 164
10.2.1.3 Statistical Analysis 164
10.2.2 Analysis 2 165
10.2.2.1 Simulations 165
10.2.2.2 Data Manipulation 166
10.2.2.3 Statistical Analysis 166
10.3 Results
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10.3.1 Analysis 1 166
10.3.2 Analysis 2 168
10.4 Discussion 171
CHAPTER 11: Other issues pertinent to EOG correction 173
11.1 Mean or Trimmed Mean B, Subject or Group? 173
11.2 Should we include non-significant Bs in the correction
stage? 174
11.3 Is it appropriate to use Bs calculated from Calibration
Trials? 176
11.3.1 Methods 181
11.3.1.1 Subjects 181
11.3.1.2 Data Acquisition 181
11.3.1.3 Procedure 181
11.3.1.4 Data Manipulation 182
11.3.1.4.1 Temporal Stability 182
11.3.1.4.2 Forward Propagation 182
11.3.1.5 Statistical Analysis 182
11.3.1.5.1 Temporal Stability 182
11.3.1.5.2 Forward Propagation 183
11.3.2 Results 183
11.3.2.1 Temporal Stability 183
11.3.2.2 Forward Propagation 185
11.3.3 Discussion 186
11.4 Summary 190
CHAPTER 12: Issues relating to the latter stage of the
correction of EOG artifact in the EEG 190
12.1 Introduction 190
12.2 How does error occur in the correction phase? 191
12.3 What is the magnitude of this error? 193
12.3.1 Assuming neural potentials originate from the electrode
site under study 193
12.3.2 Not assuming neural potentials originate from the
electrode site under study 195
12.4 What does this mean for ERP and EEG results? 196
12.5 How can we adjust for this 'correction phase' error? 201
12.5.1 Filtering 201
12.5.2 Source localization methods 203
12.5.3 The approximation adjustment 203
12.6 Assumptions of this Chapter 206
12.7 Limitations of the Approximation Adjustment 207
12.8 Other Sources of Error 208
12.9 Conclusions 209
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CHAPTER 13: Conclusions reached in this thesis 209
13.1 The same correction coefficients can correct blink and
saccade artifact 209
13.2 The frequency domain approach is not recommended 211
13.3 The RAAA procedure should be used to calculate
correction coefficients 211
13.4 Calibration trials should be employed to calculate Bs 212
13.5 Hierarchical multiple regression should be employed to
estimate Bs 212
13.6 Other issues addressed concerning B estimation 213
13.7 Issues relating to the correction phase 214
13.8 Future directions 214
13.9 Suggested EOG correction algorithm 216
REFERENCES 218
APPENDIX: Publications from this thesis 225