Event-related Synchronization/Desynchronization Affected by

Event-related Synchronization/Desynchronization Affected
by Spatial Frequencies of Background Visual Pattern during
a Cognitive Task
背景画像の空間周波数特性が認知課題遂行中の
事象関連同期/脱同期に与える影響
Kazuo Kato (Tohoku Gakuin University)
Osamu Miura (Graduate school of Tohoku Gakuin University)
加藤和夫／東北学院大学
三浦孟／東北学院大学大学院
Introduction
2
Introduction
Visual information
Color, Shape,
Movement, Depth
Spatial Frequency,
etc…
Spatial Frequency
Phyco-physiological activity ?
例：建築デザイン etc…
例：安心、快適感 etc…
3
Background
Spatial Frequency
輝度の空間的変化のパターンを表す指標
4
Background
Vuilleumier P, Armony JL, Driver J, Dolan RJ: ”Distinct spatial frequency sensitivities for
processing faces and emotional expressions,” Nature Neuroscience. 6(6): 624-631, 2003
5
Background
Our previous study
Real environmental scene
空間周波数スペクトルを
1/f の直線で近似し，そ
の傾き で定義
the slope () of its power spectral density
風景などの実空間画像に対する注視情報と空間周波数特性の傾き には，関連
があることを示している
Kato K, Shikoda A, Nishida M, Kuroki T, Ishikawa A and Kobayashi T: “Characteristics of image properties inducing eye
movement,” IEEJ Trans. EIS, Vol. 131, pp. 175-181 (2011) (in Japanese)
Neural activity were not addressed in this study
6
Background
Our previous study
We evaluated how the spatial frequency characteristics of a visual stimulus, as
indexed by the slope () of its power spectral density, affected the eventrelated potentials (ERPs) observed during a simple cognitive addition task.
(1) the low spatial frequency components may
preferentially participate in the neural activity
associated with the retrieval of arithmetic data
and that the 1/f frequency characteristics may
be optimal for playing important roles in
internal spatial processing of numbers.
Fz
(2) the most advantage of this method utilizing
a  parameter, compared to the alternative
method using high or low pass filtering for
images, is that which enables to obtain multiple
data by adopting arbitrary and consecutive 
values.
Kato K et. al.: “Event-related Potential Affected by Spatial Frequency of
Background Visual Pattern During a Cognitive Task,” IEEJ Trans 2013,
Vol.8, pp. 483-488
Cz
182 ms
360 ms
Pz
What is Event-Related Synchronization
/Desynchronization (ERS/ERD) ?
自発脳波
誘発脳波
自発的に発生している脳電位
（θ波, α波, β波）
特定の事象に関連して発生する
自発脳波リズム変動(ERS/ERD)について検討を行った
事象関連同期/脱同期(ERS/ERD)：
外的，あるいは内的な事象に関連して生じる脳波リズムの変動
ERS/ERS
Auditory
Information
Visually
Information
8
Objective
Objective
空間周波数特性に着目
タスクとして
単純な認知課題の一つである計算課題を行う
空間周波数が認知活動に関わる大脳神経活動に与える影響を評価
空間周波数特性が認知課題における自発脳波リズムに与える影響についての検討
The purpose of this study is to characterize the oscillatory changes in neural activity
associated with cognitive processes that are affected by the spatial frequency of a
visual stimulus during simple calculation tasks by using electroencephalography.
Goal
人間特性を考慮した空間設計への適用
9
Visual stimuli
White noise ( = 0)
1/f ( = 1)
1/f2 ( = 2)
1/f3 ( = 3)
10
Visual stimuli
Spatial luminance fluctuations in an image
1/f
White
Noise
1/f2
1/f
1/f2
1/f
1/f23
1/f
1/f23
1/f3
11
Visual stimuli
Slope of 2the regression curve fitted to the power spectral density
1/f
of spatial luminance fluctuations in an image
1/f
White noise
1/f
Slope : 0
1/f3
1/f21/f2
Slope : 1
1/f3
Slope : 2
Slope : 3
12
Visual stimuli
1/f3
1/f2
1/f
低周波数の影響が大きい
White noise
Power spectrum density
高周波数の影響が大きい
white noise
1/f
1/f
3
1/f 2
Frequency [Hz]
Low frequency
High frequency
13
Visual stimuli
- Randomly selected number between 0–9 embedded in each stimulus
- 4種類の模擬画像に0～9の数字を挿入した輝度3cd/m2の縦902×横1282
ピクセルの画像
30.5°
3
White noise (1/f0)
1/f
3
3
1/f2
1/f3
20°
3
1.5°
1°
14
Task
2000ms
250ms
7
1 trial
3
・・・
×25 times ×2 sets ×4 stimulus
- Each 250-ms stimulus was presented 25 times per set and the numbers
were repeated twice for a total of 50 stimulus presentations
7
3
・・・
(1) Addition task (計算有タスク)
(2) Reference task (参照タスク)
adding
7
No adding
adding
3
No adding
・・・
15
Methods
EEG measurement
・ Subjects: 8 males (age, 21-23)
- All participants provided written informed consent
・ 19 electrodes based on the 10-20 system
- Reference electrodes: Linked electrode at both ears
- Impedance < 10kΩ
16
Methods
Data analysis
・ Continuous Wavelet
Transform
- with the mother function of morlet were conducted for each EEG epoch from
1 to 80 Hz per 0.1 Hz
・ Intertrial Variances
- of the wavelet coefficients for each frequency per 0.1 Hz were calculated using
the equation below
where N = 50 at maximum, indicating the total number of trials, xf(i,j) denotes
the j-th sample (wavelet coefficients) of the i-th trial, and represents the mean
of data at the j-th sample.
・Band Average Variances
- in the theta(4–6 Hz), alpha (8–13 Hz), low beta (13–20 Hz), and gamma (40–80
Hz) frequency ranges were also calculated and the 500-ms prestimulus period
served as the value for baseline normalization.
17
Flow of analysis
Step1: Comparison between addition and reference task
認知活動の
比較
• 計算有・無タスク間の分散の比較(time-frequency analysis)
• 特徴帯域毎の分散の時間変化の検討(time course)
• 特徴帯域毎の分散の空間分布の検討(spatial distribution)
Step2: Comparison among stimuli
空間周波数
特性の比較
• 各空間周波数特性刺激に対する分散の変動の比較
18
Flow of analysis
Step1: Comparison between addition and reference task
認知活動の
比較
• 計算有・無タスク間の分散の比較(time-frequency analysis)
• 特徴帯域毎の分散の時間変化の検討(time course)
• 特徴帯域毎の分散の空間分布の検討(spatial distribution)
Step2: Comparison among stimuli
空間周波数
特性の比較
• 各空間周波数特性刺激に対する分散の変動の比較
19
Overall mean intertrial variances
Pz
O2
(a) Addition task
(b) Reference task
(c) Addition - Reference
20
Flow of analysis
Step1: Comparison between addition and reference task
認知活動の
比較
• 計算有・無タスク間の分散の比較(time-frequency analysis)
• 特徴帯域毎の分散の時間変化の検討(time course)
• 特徴帯域毎の分散の空間分布の検討(spatial distribution)
Step2: Comparison among stimuli
空間周波数
特性の比較
• 各空間周波数特性刺激に対する分散の変動の比較
21
Time Course of band-averaged variances
Addition Task
Reference Task
Alpha (8-13Hz) at O2
Theta (4-6 Hz) at O2
376ms
198ms
Gamma (40-80 Hz) at Pz
Low Beta (13-20 Hz) at Pz
1,012ms
490ms
1,742ms
22
Flow of analysis
Step1: Comparison between addition and reference task
認知活動の
比較
• 計算有・無タスク間の分散の比較(time-frequency analysis)
• 特徴帯域毎の分散の時間変化の検討(time course)
• 特徴帯域毎の分散の空間分布の検討(spatial distribution)
Step2: Comparison among stimuli
空間周波数
特性の比較
• 各空間周波数特性刺激に対する分散の変動の比較
23
Differential Topographical Map (Addition - Reference Task)
: p < 0.05
(a) Theta band
20 [%]
1/f
1/f2
(b) Alpha band
-20
0 [%]
1/f2
1/f3
-20
24
Differential Topographical Map (Addition - Reference Task)
: p < 0.05
(c) Low Beta band
25 [%]
(d) Gamma band
-25
1/f3
1/f
20 [%]
Fp1
Fp2
F7 F3 Fz F4 F8
T3 C 3 C z C 4 T4
T5 P3 Pz P4 T6
O1
1/f2
-20
O2
25
Flow of analysis
Step1: Comparison between addition and reference task
認知活動の
比較
• 計算有・無タスク間の分散の比較(time-frequency analysis)
• 特徴帯域毎の分散の時間変化の検討(time course)
• 特徴帯域毎の分散の空間分布の検討(spatial distribution)
Step2: Comparison among stimuli
空間周波数
特性の比較
• 各空間周波数特性刺激に対する分散の変動の比較
26
120
*
* p < 0.05
*
110
100
90
80
White noise
1/f *
1/f2
Visual stimuli
1/f3
Normalized variance  S.E. [%]
Normalized variance  S.E. [%]
Results and Discussion
120
110
* p < 0.05
*
*
100
90
80
White noise
(a) Theta at F4
1/f *
1/f2
Visual stimuli
1/f3
(b) Theta at C4
Theta band (198ms, fronto-central area)
- ERS for the 1/f and ERD for the 1/f2 stimulus
- A linear change in variance in response to a
frequency change
- This phenomenon may suggest the existence of a
neural
frequency
discrimination
function
accompanying simple cognitive calculations
27
120
* p < 0.05
110
*
100
90
80
White noise
1/f * 1/f2
Visual stimuli
1/f3
Normalized variance  S.E. [%]
Normalized variance  S.E. [%]
Results and Discussion
120
* p < 0.05
*
110
100
90
80
White noise
(c) Alpha at T5
* 1/f2
1/f
Visual stimuli
1/f3
(d) Alpha at P3
Alpha band (376ms, left-temporal area)
- In the reference task, the alpha-ERD associated with high spatial frequencies
may suggest the importance of the left hemisphere area over areas associated
with early visual processing .
- In the addition task, all frequencies activate neural processes suggest to relate
to the retrieval of arithmetic data calculations and the interpretation of
operation symbols.
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Conclusion
- A frequency discrimination function has been suggested to exist at a latency
of 198 ms in the theta band activity recorded in the addition task from the
fronto-central area.
- The alpha ERD in the reference task at the left temporal-parietal area at the
latency of 376 ms also showed a spatial frequency dependency concerned
with perceptual filter.
- The frequency dependence of low Beta and Gamma bands could not be
confirmed from our data set.
Therefore, we suggest that oscillatory changes in the neural activity associated
with cognitive processes affected by spatial frequency occur along with ERP
responses.
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