Article

Gratton G, Coles MG, Donchin E. A new method for off-line removal of ocular artifact

Cognitive Psychophysiology Laboratory, Department of Psychology, University of Illinois, Champaign, Ill. 61820 U.S.A.
Electroencephalography and Clinical Neurophysiology 05/1983; 55(4):468-84. DOI: 10.1016/0013-4694(83)90135-9
Source: PubMed

ABSTRACT

A new off-line procedure for dealing with ocular artifacts in ERP recording is described. The procedure (EMCP) uses EOG and EEG records for individual trials in an experimental session to estimate a propagation factor which describes the relationship between the EOG and EEG traces. The propagation factor is computed after stimulus-linked variability in both traces has been removed. Different propagation factors are computed for blinks and eye movements. Tests are presented which demonstrate the validity and reliability of the procedure. ERPs derived from trials corrected by EMCP are more similar to a 'true' ERP than are ERPs derived from either uncorrected or randomly corrected trials. The procedure also reduces the difference between ERPs which are based on trials with different degrees of EOG variance. Furthermore, variability at each time point, across trials, is reduced following correction. The propagation factor decreases from frontal to parietal electrodes, and is larger for saccades than blinks. It is more consistent within experimental sessions than between sessions. The major advantage of the procedure is that it permits retention of all trials in an ERP experiment, irrespective of ocular artifact. Thus, studies of populations characterized by a high degree of artifact, and those requiring eye movements as part of the experimental task, are made possible. Furthermore, there is no need to require subjects to restrict eye movement activity. In comparison to procedures suggested by others, EMCP also has the advantage that separate correction factors are computed for blinks and movements and that these factors are based on data from the experimental session itself rather than from a separate calibration session.

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    • "The raw data were off-line downscaled to a sampling rate of 1000 Hz, band-pass filtered (cutoff frequencies 0.05 and 17 Hz), re-referenced to linked mastoids, and segmented into 1300 ms stimulus-locked epochs covering the period from −100 to 1200 ms relative to tone onset, using the Brain Vision Analyzer software (version 1.05; Brain Products , Munich, Germany). The data were corrected for ocular artifacts using the Gratton and Coles procedure (Gratton et al. 1983). Individual epochs exceeding a maximum– minimum difference of 300 µV were excluded from further analysis (automatic artifact rejection as implemented in the Brain Vision Analyzer software). "
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    • "Off-line EEG analysis was performed using Vision Analyzer software (BrainProducts). The data were digitally low-passfiltered at 30 Hz (12 dB/oct), and ocular correction was performed (Gratton et al., 1983). Epochs of 600 ms were extracted from the raw EEG data from 100 ms before the face onset to 500 ms after the face onset. "

    Full-text · Dataset · Nov 2015
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    • "Horizontal eye movements (electro-oculogram, EOG) were monitored with a bipolar recording from electrodes at the left and right outer canthi. Blinks and vertical eye movements were recorded with electrodes below and above the left eye and artifacts were reduced through the Gratton et al. (1983) algorithm. Computerized artifact rejection was further performed prior to the signal averaging, discarding epochs with amplitudes exceeding 80 V peak to peak Using the BrainVision TM Analyzer 2.1 software (BrainProducts GmbH., Munich, Germany), the "
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