Reduction of non-periodic environmental magnetic noise in MEG measurement by continuously adjusted least squares method

Adachi, Yoshiaki; Shimogawara, Masahiro; Higuchi, Masanori; Haruta, Yasuhiro; Ochiai, Minoru

doi:10.1109/77.919433

Cited by 139 publications

(121 citation statements)

References 3 publications

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“…Data for the main (interaural correlation) experiment were acquired continuously with a sampling rate of 1 kHz, filtered in hardware between 1 and 200 Hz, with a notch at 60 Hz (to remove line noise), and stored for later analysis. Effects of environmental magnetic fields were reduced based on several sensors distant from the head using the continuously adjusted least squares method (Adachi et al, 2001), and responses were then smoothed by convolution with a 39 ms Hanning window (cutoff, 55 Hz). These are standard signal processing methods; additional processing is described below.…”

Section: Neuromagnetic Recording and Data Analysismentioning

confidence: 99%

Human Auditory Cortical Processing of Changes in Interaural Correlation

Chait¹,

Poeppel²,

Cheveigné³

et al. 2005

J. Neurosci.

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Sensitivity to the similarity of the acoustic waveforms at the two ears, and specifically to changes in similarity, is crucial to auditory scene analysis and extraction of objects from background. Here, we use the high temporal resolution of magnetoencephalography to investigate the dynamics of cortical processing of changes in interaural correlation, a measure of interaural similarity, and compare them with behavior. Stimuli are interaurally correlated or uncorrelated wideband noise, immediately followed by the same noise with intermediate degrees of interaural correlation. Behaviorally, listeners' sensitivity to changes in interaural correlation is asymmetrical. Listeners are faster and better at detecting transitions from correlated noise than transitions from uncorrelated noise. The cortical response to the change in correlation is characterized by an activation sequence starting from ϳ50 ms after change. The strength of this response parallels behavioral performance: auditory cortical mechanisms are much less sensitive to transitions from uncorrelated noise than from correlated noise. In each case, sensitivity increases with interaural correlation difference. Brain responses to transitions from uncorrelated noise lag those from correlated noise by ϳ80 ms, which may be the neural correlate of the observed behavioral response time differences. Importantly, we demonstrate differences in location and time course of neural processing: transitions from correlated noise are processed by a distinct neural population, and with greater speed, than transitions from uncorrelated noise.

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Section: Neuromagnetic Recording and Data Analysismentioning

confidence: 99%

Human Auditory Cortical Processing of Changes in Interaural Correlation

Chait¹,

Poeppel²,

Cheveigné³

et al. 2005

J. Neurosci.

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show abstract

“…This involves finding a matrix C = [c kj ] such that the linear combination Cr(t) of reference signals best approximates s(t) in a least-squares sense. Several denoising methods proceed in this way, for example CALM [10]. For the second model (convolutive mixing), the previous solution does not work because a linear combination cannot effectively mimick or reverse the effects of convolutive mixing.…”

Section: Algorithms and Implementationmentioning

confidence: 99%

MEG Signal Denoising Based on Time-Shift PCA

Cheveigné¹,

Roux

Simon

2007

2007 IEEE International Conference on Acoustics, Speech and Signal Processing - ICASSP '07

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We present a method for removing environmental noise from physiological recordings such as Magnetoencephalography (MEG) for which noise-sensitive reference channels are available. Sensor signals are projected on a subspace spanned by the reference channels augmented by time-shifted and/or nonlinearly transformed versions of the same, and the projections are removed to obtain "clean" sensor signals. The method compensates for scalar, convolutional or non-linear mismatches between sensor and reference channels by synthesizing, for each reference/sensor pair, a filter that is optimal in a least-squares sense for removal of the artifact. The method was tested with synthetic and real MEG data, typically removing up to 98% of noise variance. It offers an alternative to bulky and costly magnetic shielding (multiple layers of aluminium and mu-metal) for present scientific and medical applications and future developments such as brainmachine interfaces (BMI).

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“…The magnetic responses were filtered by a bandpass filter from 0.1 to 200 Hz and digitized at a sampling rate of 1,000 Hz. For off-line analysis, the nonperiodic low-frequency noise in the MEG raw data was reduced using a continuously adjusted least-squares method (Adachi et al 2001). The resulting data were then filtered by a bandpass FIR filter from 0.5 to 50 Hz after removing artifacts with amplitudes exceeding 3,000 fT/cm in the MEG signals.…”

Section: Data Acquisitionmentioning

confidence: 99%

Coherent activity between auditory and visual modalities during the induction of peacefulness

Yang

Lin²

2012

Cogn Neurodyn

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Multisensory integration involves combining information from different senses to create a perception. The diverse characteristics of different sensory systems make it interesting to determine how cooperation and competition contribute to emotional experiences. Therefore, the aim of this study were to estimate the bias from the match attributes of the auditory and visual modalities and to depict specific brain activity frequency (theta, alpha, beta, and gamma) patterns related to a peaceful mood by using magnetoencephalography. The present study provides evidence of auditory domination in perceptual bias during multimodality processing of peaceful consciousness. Coherence analysis suggested that the theta oscillations are a transmitter of emotion signals, with the left and right brains being active in peaceful and fearful moods, respectively. Notably, hemispheric lateralization was also apparent in the alpha and beta oscillations, which might govern simple or pure information (e.g. from single modality) in the right brain but complex or mixed information (e.g. from multiple modalities) in the left brain.

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Reduction of non-periodic environmental magnetic noise in MEG measurement by continuously adjusted least squares method

Cited by 139 publications

References 3 publications

Human Auditory Cortical Processing of Changes in Interaural Correlation

Human Auditory Cortical Processing of Changes in Interaural Correlation

MEG Signal Denoising Based on Time-Shift PCA

Coherent activity between auditory and visual modalities during the induction of peacefulness

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