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Removal of ocular artifacts from EEG using adaptive thresholding of wavelet coefficients

V Krishnaveni1, S Jayaraman1, L Anitha1 and K Ramadoss2

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Electroencephalogram (EEG) gives researchers a non-invasive way to record cerebral activity. It is a valuable tool that helps clinicians to diagnose various neurological disorders and brain diseases. Blinking or moving the eyes produces large electrical potential around the eyes known as electrooculogram. It is a non-cortical activity which spreads across the scalp and contaminates the EEG recordings. These contaminating potentials are called ocular artifacts (OAs). Rejecting contaminated trials causes substantial data loss, and restricting eye movements/blinks limits the possible experimental designs and may affect the cognitive processes under investigation. In this paper, a nonlinear time-scale adaptive denoising system based on a wavelet shrinkage scheme has been used for removing OAs from EEG. The time-scale adaptive algorithm is based on Stein's unbiased risk estimate (SURE) and a soft-like thresholding function which searches for optimal thresholds using a gradient based adaptive algorithm is used. Denoising EEG with the proposed algorithm yields better results in terms of ocular artifact reduction and retention of background EEG activity compared to non-adaptive thresholding methods and the JADE algorithm.


PACS

87.80.-y Biophysical techniques (research methods)

02.30.Uu Integral transforms

87.19.X- Diseases

87.19.R- Mechanical and electrical properties of tissues and organs

87.19.L- Neuroscience

Subjects

Mathematical physics

Instrumentation and measurement

Medical physics

Biological physics

Dates

Issue 4 (December 2006)

Received 10 January 2006, accepted for publication 27 October 2006

Published 23 November 2006



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