Technical sectionA new method for off-line removal of ocular artifactNouvelle méthode d'élimination off-line des artéfacts oculaires☆
Abstract
A new off-line procedure for dealing with ocular artifacts in ERP recording is described. The procedure (EMPC) 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-linkes 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.
Résumé
Une nouvelle technique ‘off-line’ pour éliminer les artéfacts oculaires lors de l'enregistrement des PER est décrite. La technique ‘EMCP’ utilise les enregistrements de l'EOG et de l'EEG au cours d'essais individuels d'une session expérimentale, pour déterminer un facteur de propagation décrivant la relation entre tracés EOG et EEG. Le facteur de propagation est calculé après que la variabilité liée au stimulus est été éliminée sur les deux tracés. Différents facteurs de propagation sont calculés pour les clignements de paupières et les mouvements oculaires.
Des tests démontrant la validité et la fiabilité de la technique sont présentés. Les PER obtenus à partir d'essais corrigés par la EMCP ressemble davantage à un ‘vrai’ PER qu'un PER obtenu à partir d'essais, soit non corrigés, soit corrigés au hasard. La méthode réduit également la différence entre PER recueillis lors d'essais avec différents degré de variance de l'EOG. De plus la variabilitéà chaque instant entre les essais est réduite après correction.
Le facteur de propagation décroît des électrodes frontales aux électrodes pariétales, il est plus grand pour des saccades que pour des clignements. Il est plus stable à l'intérieur d'une session que d'une session à l'autre.
L'avantage majeur de la méthode est de pouvoir retenir tous les essais dans une expérience de PER, quels que soient les artéfacts oculaires. Ainsi les études de populations caractérisées par un grand nombre d'artéfacts et celles nécessitant des mouvements oculaires comme partie intégrante de l'expérience, sont devenues possibles. De plus, il n'est pas nécessaire de demander au sujet de limiter son activité motrice oculaire.
Par rapport à des techniques proposées par d'autres l'EMCP a aussi l'avantage d'établir des facteurs de correction séparés pour les clignements de paupières et les mouvements oculaires. Ces facteurs sont basés sur des données recueillies lors de la séance expérimentale elle-même, et non à partir d'une séance d'étalonnage séparée.
References (13)
- D.G. Girton et al.
Simple on-line technique for removing eye movement artifacts from the EEG
Electroenceph. clin. Neurophysiol.
(1973) - S.A. Hillyard et al.
Eye movement artifact in the CNV
Electroenceph. clin. Neurophysiol.
(1970) - W. Barry et al.
Influence of eyelid movement upon electro-oculographic recording of vertical eye movements
Aerospace Med.
(1965) - A. Carpenter
The rate of blinking during prolonged visual search
J. exp. Psychol.
(1948) - J.C. Corby et al.
Differential contributions of blinks and vertical eye movements as artifacts in EEG recording
Psychophysiology
(1972) - E. Donchin et al.
Publication criteria for studies of evoked potentials (EP) in man. Report of the Methodology Committee
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This research reported here has been supported under the Office of Naval Research (Contract No. N00014-76-C-0002) with funds provided by the Defense Advanced Research Projects Agency; AFOSR under Contract No. F49620-79C-0233; Wright Patterson AFB under Contract No. F33615-79C-0512; and the Environmental Protection Agency under Contract No. R805628010.