Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu...
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![Page 1: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/1.jpg)
Study of Change Blindness EEG
Synchronization using Wavelet Coherence
Analysis
Professor: Liu
Student: Ruby
![Page 2: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/2.jpg)
Motivation & Purpose
• Motivation – The authors wanted to know the brain activity
during the visual detect the change.
• Purpose– Using a wavelet coherence analysis for test the
multi-channel EEG signals when people do the change detection and change blindness.
![Page 3: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/3.jpg)
References
• Two explanations for change blindness:– Visual memory can encoding the information, b
ut can not record all changes.– Visual memory has limitation during the pictur
es was changed. (Markazi et al., 2005)
• Comparing brain activity during change detection and change blindness. (Beck et al., 2001)
![Page 4: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/4.jpg)
The change blindness experiment
• Participants – 9 people whose age from
19-55 years old, have normal vision.
• Material – The topic of the pictures
were faces and places.– EEG signals were taken
1000 Hz from 32 electrodes, 10-20 system.
![Page 5: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/5.jpg)
The change blindness experiment
• Procedure (Main task was to detect a change in the pictures between the two stimulus.)– Step 1: first stimulus included two pictures, display for
500 ms.– Step 2 : 500ms blank display.– Step 3 : second stimulus included two pictures, display
for 500ms.– Step 4 : 500ms blank display.
• Second task was search the letter which was showed at the top and bottom of the screen.
![Page 6: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/6.jpg)
Wavelet coherence method
• The wavelet transform used for investigating the basic characteristics of the non-stationary EEG signals.
• Using the continuous Wavelet Transform (CWT).
• The CWT of a signal x(u) is a function of time (τ) and frequency (f).
![Page 7: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/7.jpg)
Wavelet coherence method
• The continuous wavelet transform of a signal x(u) is a function of time (τ) and frequency (f).
• Choosing the Morlet wavelet.
• The wavelet cross-spectrum between x and y.
• wavelet coherence WCo (t,f) is defined as:
![Page 8: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/8.jpg)
Wavelet coherence analysis
• The length of each epoch was 2000 ms.
• Epochs were classified into four types:
(i) Hit (H)
(ii) Miss (M)
(iii) No- change (correct detection)
(iv) False alarm.
• Only focused on the miss and hit.
![Page 9: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/9.jpg)
Wavelet coherence analysis
Fig. 2: (a) Wavelet coherence map of one epoch for
miss trial between channel FP1 and F3. (b) Wavelet coherence map of one epoch fo
r hit trial between channel FP1 and F3.
The higher coherence
value, the more the
two channels are
synchronized which is
presented as dark areas.
![Page 10: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/10.jpg)
Wavelet coherence analysis
Less degree of coherency comparing to Fig.2.
Fig. 3:(a) Wavelet coherence map of one epoch for
miss trial between channel P8 and C3. (b) Wavelet coherence map of one epoch for
hit trial between channel P8 and C3.
![Page 11: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/11.jpg)
Wavelet coherence analysis• WCO of hit and miss trial were significant differences.
• Fig. 4: P-value maps for WCO of hit and miss trial with p-
value<0.01
(a) The p-value calculated for the pair channels FP1 and F3.
(b) The p-value calculated for the pair channels P8 and C3.
![Page 12: Study of Change Blindness EEG Synchronization using Wavelet Coherence Analysis Professor: Liu Student: Ruby.](https://reader036.fdocuments.in/reader036/viewer/2022062304/56649c7b5503460f9492efd2/html5/thumbnails/12.jpg)
Conclusion
• The frontal electrodes showed higher differences between WCO of hit and miss trials.
• There are different degrees of cross synchronicity and information exchange patterns during visual cognitive activity.