Types of Tools
• Filter
• Segmentation
• Visual Review
• Artifact Detection, Bad Channel Correction, Baseline Correction, Average Reference (Montage Operation), Averaging
• Move on to Statistical Analyses
Friday, January 14, 2011
FilteringFiltering reduces total frequencies by specific amounts: 60 Hz (50 Hz in Europe) Typical: 0.1 - 100 Hz
200 Series Amps: Select Low Pass (30 Hz)
Friday, January 14, 2011
Filtering300 Series Amps (portables): First filtered using “First Order High Pass Filter” = 0.1 Then settings used in last slide.
Do NOT mix data from 200 & 300 series amplifiers in any one study.
If conducting a series of related studies, may want to use the same amplifiers.
Friday, January 14, 2011
More Filtering
• Filter to the level that you will analyze
• Can process a file many different ways
• e.g. Once at 0.1 to 30 hz and once at theta
• Filter all files in a project to the same level
• Filters are additive
• Data change every time they are filtered!
Friday, January 14, 2011
Segmentation
• Original data recorded is continuous EEG with markers included indicating stimulus events and subject response events (if programmed: e-prime).
• Segmentation breaks ongoing EEG into epochs
• Segment on stimulus, response, blink, startle, etc.
• Create categories for each stimulus
• Look for easy way to categorize trials into correct and incorrect responses
Friday, January 14, 2011
Visual InspectionCheck Eye channels:
Could be bad because not contacting skin OR detecting eye blinks or eye movements.
If bad across high number of trials, bad electrode and must be marked “BAD” for entire recording session would fail because of eye artifacts.
Friday, January 14, 2011
Visual InspectionCheck Eye channels:
Could be bad because not contacting skin OR detecting eye blinks or eye movements.
If bad across high number of trials, bad electrode and must be marked “BAD” for entire recording session would fail because of eye artifacts.
Friday, January 14, 2011
Automating Analyses: Constructing a Script
• Script step 1
• Filtering, then Segmentation
• You must filter before segmentation as filters flatten data at the beginning and end of each epoch
Friday, January 14, 2011
Automating Analyses: Constructing a Script
• Script step 1
• Filtering, then Segmentation
• You must filter before segmentation as filters flatten data at the beginning and end of each epoch
Friday, January 14, 2011
Order of Operations
• Still have left:
• Artifact Detection
• Bad Channel Correction
• Baseline Correction
• Average Reference
• Averaging
• “Does order make difference?” controversy
Friday, January 14, 2011
Artifact Detection
• Examines segments for bad channels, eye blinks, and eye movements
• Can define artifacts by threshold
• Max-Min = 200µV is bad channel over segment
• Can define artifacts by slope of line
• Terms: fast-average, fast-amplitude
• Can define artifacts by modeling examples
• BESAFriday, January 14, 2011
Artifact DetectionBad Channel Scan
- shorted electrodes - bad scalp connection - 200 µV over segment
Eye Blinks & Movement - between electrodes pair - differ by net type
Friday, January 14, 2011
Artifact DetectionEye Blinks & Movement
- between electrodes pair - differ by net type
Friday, January 14, 2011
Things to Look Out For
• Problem: The algorithms can be too simple
• If eye channels detect an eye movement or blink, may mark the segment bad
• If an eye channel is bad, may mark all segments bad
Friday, January 14, 2011
Strategies
• First: Inspect Eye Channels
• Check impedance levels from records
• Have Artifact Detection check for you.
• Second: Interpolate those bad channels
• Spherical Interpolation
• Third: Continue processing files
• Baseline, Average Reference, Average
Friday, January 14, 2011
“Automated ICA”
• Joyce, C.A., Gorodntsky, I.F., Kutas, M. (2004)
• Automatic removal of eye movement and blink artifacts from EEG data using blind component separation
Friday, January 14, 2011
Bad Channel Replacement
No User Settings - Interpolates Missing ChannelsUsing Weighted Average
Friday, January 14, 2011
Average• Important Strategies to keep in mind:
• Equal Number of Averages / Condition
• Equal Number of Averages / Subject
• Weighted Averaging
• Random Selection of Trials
• Early vs. Late in Experiment
Friday, January 14, 2011
Average Reference
• Re-referencing data
• Defining a new “zero point”
• Average Reference
Friday, January 14, 2011
Baseline Correction
• De-trend data from long slow oscillations in waveform
Friday, January 14, 2011
Baseline Correction• Pre-stimulus period, usually 100-200 ms
• Average value for pre-stimulus points in baseline is calculated
• Average value subtracted from post-stimulus period
• Important to avoid artifacts in baseline period!
Friday, January 14, 2011
Average Reference
Data originally recorded represent differencebetween an electrode & reference (Cz)
To reduce bias of particular reference, data re-referenced to the average reference
Friday, January 14, 2011
AveragingAverage together all trials of particular stimulus (or condition) to form single waveform (average) composed of ALL presentations of that stimulus (or condition). Averaging = noise reduction technique
Study: Randomly presented 100 /ba/ syllables intermixedwith 100 presentations of /ga/.
Separate averages constructed for /ba/ and /ga/, each based on their separate ~100 presentations.
Friday, January 14, 2011
Controversy of Order
• Early vs. Late Baseline Correction
• baseline changes the data
• OAR must be followed by baseline fix*
• Early vs. Late Re-Referencing of data
• Average Reference changes the data
• Early vs. Late Averaging
• Better to average before/after baseline & referencing?
Friday, January 14, 2011
1. Average
2. Average Reference
3. Baseline Correction
1. Ave Ref then Average
2. Baseline Correct
1. Baseline then Ave
2. Ave RefFriday, January 14, 2011
Benefits of Automation
• Increases Replicability
• Fairly easy to teach analysis steps
• High inter-rater reliability
• Batch processing of files
Friday, January 14, 2011
• Peak Amplitude & Latency
• Define a window
• Have tool extract information from waveform
• Problems:
• Variability in waveforms trial-to-trial
• Variability from electrode to electrode
Statistical Extractions
Friday, January 14, 2011
Export From NS
• Two Steps
• Convert to Text Files
• Use Matlab to Combine/Rotate Data
Friday, January 14, 2011
Change NS files from AVG to RAW: (1) Use NS File Exporter (in Extras folder of NS) Drag and drop AVE files Caution - name change (older version bug) (2) If names altered, use “Convert to Text” in Net Station or “Net Station File Exporter 2.1”
(3) Gives floating point simple binary conversion.
“RM_4452f_1_6x25.ave” --> “RM_4452f_1_6x25.RAW””
Friday, January 14, 2011
(2) Text Export 2.1 program Converts RAW to Text
Drag in RAW files, click “CONVERT” to generate TEXT files.
Friday, January 14, 2011
3. Can ALSO covert to text using FIILE EXPORT TOOL in “Net station Waveform Tools”.
!
Friday, January 14, 2011
MCAT
Three Functions
1. Rotate data matrix for input to stat programs.2. Concatenate subject data text files.3. Combine electrode sites into regional electrodes.
Friday, January 14, 2011
Rotate Data Matrix
Channel 1Data Pt 1
Channel 2Data Pt 1
Channel 3Data Pt 1
Channel 1Data Pt 2
Channel 2Data Pt 2
Channel 3Data Pt 2
Channel 1Data Pt 3
Channel 2Data Pt 3
Channel 3Data Pt 3
Channel 1Data Pt 1
Channel 1Data Pt 2
Channel 1Data Pt 3
Channel 2Data Pt 1
Channel 2Data Pt 2
Channel 2Data Pt 3
Channel 3Data Pt 1
Channel 3Data Pt 2
Channel 3Data Pt 3
BEFORE AFTER
MCAT
Suitable for Temporal PCASuitable for Spatial PCA
Friday, January 14, 2011
REF
CZ
101
Pz
COM
15387
36 224
59
C3
183
C4
21
37 18
47
F7
2
F8
116 150
17096
202
T4
69
T3
13
4
5
6
7
8
9
1011
12
13
14
15
Fz
16
17
19
Fp2
20
22
23
24
25
26
27
28
29
30
31
32
33
Fp1
34
35
38
39
40
41
F3
42
43
44
45
46
48
49
50
51
52
53
54
55
56
57
58
60
61
62
63
64
65
66
67
68
70
7172
186
198
207
215
74
7576 77
7879
80
81
73
253
252
248
249
254
255
256
251
250
241
244
242
245
243
246
247
82
83
8485
86
P3
88
89
90
91
92
9394
LM95
T5 9798
99
100
102
103
104105
106 107108
109
110
111
112
113 114115
117
118
119
120 121 122123
124
O1
125
126
127
128
129
130
131
133134
135
136
137
Oz
138
139
140
141
142
143
145
146
147
148
149
O2
151
152
154
155
156
157
158
159
160
161
162
P4
163
164173
165
166
S/N
174
167
168
169
171
172
132144
175
176
177
178
T6
179
180
181
182
187
188
189
190
RM
191
192
193
194184185
195196
197
199
200
201
210
208
209
216
217
218
203
204205
206
214
F4
211
212213 219
220
221222
223 225
226
227
228
229
230
231
232
233
234235
236
237
238 239240
HydroCel Geodesic Sensor Net
256 Channel MapVersion 1.0
For questions or additional assistance please refer to the EGI Sensor Net Technical Manual or contact us at:
Electrical Geodesics, Inc.
1600 Millrace Drive, Suite 307
Eugene, Oregon 97403
Phone: (541) 687-7962 Fax:(541) 687-7963
Email: [email protected] or [email protected]
Combine Electrodes into Regional Electrodes
Friday, January 14, 2011
REF
CZ
101
Pz
COM
15387
36 224
59
C3
183
C4
21
37 18
47
F7
2
F8
116 150
17096
202
T4
69
T3
13
4
5
6
7
8
9
1011
12
13
14
15
Fz
16
17
19
Fp2
20
22
23
24
25
26
27
28
29
30
31
32
33
Fp1
34
35
38
39
40
41
F3
42
43
44
45
46
48
49
50
51
52
53
54
55
56
57
58
60
61
62
63
64
65
66
67
68
70
7172
186
198
207
215
74
7576 77
7879
80
81
73
253
252
248
249
254
255
256
251
250
241
244
242
245
243
246
247
82
83
8485
86
P3
88
89
90
91
92
9394
LM95
T5 9798
99
100
102
103
104105
106 107108
109
110
111
112
113 114115
117
118
119
120 121 122123
124
O1
125
126
127
128
129
130
131
133134
135
136
137
Oz
138
139
140
141
142
143
145
146
147
148
149
O2
151
152
154
155
156
157
158
159
160
161
162
P4
163
164173
165
166
S/N
174
167
168
169
171
172
132144
175
176
177
178
T6
179
180
181
182
187
188
189
190
RM
191
192
193
194184185
195196
197
199
200
201
210
208
209
216
217
218
203
204205
206
214
F4
211
212213 219
220
221222
223 225
226
227
228
229
230
231
232
233
234235
236
237
238 239240
HydroCel Geodesic Sensor Net
256 Channel MapVersion 1.0
For questions or additional assistance please refer to the EGI Sensor Net Technical Manual or contact us at:
Electrical Geodesics, Inc.
1600 Millrace Drive, Suite 307
Eugene, Oregon 97403
Phone: (541) 687-7962 Fax:(541) 687-7963
Email: [email protected] or [email protected]
Combine Electrodes into Regional Electrodes
Friday, January 14, 2011
LOR 22 26 27 28 29 32 33 34 35 37 38 39 46 47 54ROR 1 2 3 4 5 10 11 12 13 14 18 19 20 21 25 31LIF 241 242 243 244 245 246 247 248 249 250 251 252 253 254RIF 225 226 227 230 231 232 233 234 235 236 237 238 239 240LPF 9 15 16 17 23 24 30 36 40 41 42 43 44 48 49 50 51RPF 6 7 8 185 186 197 197 198 205 206 207 213 214 215 222 223 224LIT 73 82 91 92 93 102 103 111 255 256RIT 199 200 201 208 209 216 217 218 228 229LT 55 56 57 58 61 62 63 64 67 68 69 70 71 74 75 76 83RT 172 180 181 191 192 193 194 195 202 203 204 210 211 212 219 220 221LP 45 52 53 59 60 65 66 72 77 78 79 80 81 86 87 88 89 97 98 99 100 101 110RP 90 119 128 129 130 131 132 141 142 143 144 152 153 154 155 161 162 163 164 173 182 183 184LTP 84 85 94 95 96 104 105 106 112 113RTP 169 170 171 176 177 178 179 188 189 190LO 107 108 109 114 115 116 117 118 120 121 122 123 124 125 137RO 126 127 138 139 140 149 150 151 158 159 160 167 168 175 187LIO 133 134 135 136 145 146RIO 147 148 156 157 165 166 174
18 Regions - 256 HydroCel
Friday, January 14, 2011
• Benefits:
• Temporal PCA
• Plotting Programs
• DeltaGraph, Excel, BLOT
• Mathematica Imports
Friday, January 14, 2011
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