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


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.

114 Reads
  • Source
    • "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. "

  • Source
    • "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 "
    [Show abstract] [Hide abstract]
    ABSTRACT: Deciding whether to act or not to act is a fundamental cognitive function. To avoid incorrect responses, both reactive and proactive modes of control have been postulated. Little is known, however, regarding the brain implementation of proactive mechanisms, which are deployed prior to an actual need to inhibit a response. Via a combination of electrophysiological and neuroimaging measures (recorded in 21 and 16 participants, respectively), we describe the brain localization and timing of neural activity that underlies the anticipatory proactive mechanism. From these results we conclude that proactive control originates in the inferior Frontal gyrus, is established well before stimulus perception and is released concomitantly with stimulus appearance. Stimulus perception triggers early activity in the anterior Insula and Intraparietal cortex contralateral to the responding hand; these areas likely mediate the transition from perception to action. The neural activities leading to the decision to act or not to act are described in the framework of a three-stage model that includes perception, action and anticipatory functions taking place well before stimulus onset.
    NeuroImage 11/2015; DOI:10.1016/j.neuroimage.2015.11.036 · 6.36 Impact Factor
  • Source
    • "Each active electrode was measured online with respect to a common mode sense (CMS) active electrode producing a monopolar (nondifferential ) channel and was referenced offline to the average of the left and right mastoids. Data were high-pass filtered at 0.1 Hz and low-pass filtered at 30 Hz. Ocular and eyeblink artifacts were corrected using the method of Gratton et al. (1983). Epochs with other artifacts (a gradient greater than 30 μV, slow drifts [>300 μV/200 ms], and low activity [<0.50 μV/100 ms]) were discarded (placebo 1.2 %, clonidine 1.3 %, and scopolamine 2.5 %). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Rationale: The specific role of neuromodulator systems in regulating rapid fluctuations of attention is still poorly understood. Objectives: In this study, we examined the effects of clonidine and scopolamine on multiple target detection in a rapid serial visual presentation task to assess the role of the central noradrenergic and cholinergic systems in temporal attention. Method: Eighteen healthy volunteers took part in a crossover double-dummy study in which they received clonidine (150/175 μg), scopolamine (1.2 mg), and placebo by mouth in counterbalanced order. A dual-target attentional blink task was administered at 120 min after scopolamine intake and 180 min after clonidine intake. The electroencephalogram was measured during task performance. Results: Clonidine and scopolamine both impaired detection of the first target (T1). For clonidine, this impairment was accompanied by decreased amplitudes of the P2 and P3 components of the event-related potential. The drugs did not impair second-target (T2) detection, except if T2 was presented immediately after T1. The attentional blink for T2 was not affected, in line with a previous study that found no effect of clonidine on the attentional blink. Conclusions: These and other results suggest that clonidine and scopolamine may impair temporal attention through a decrease in tonic alertness and that this decrease in alertness can be temporarily compensated by a phasic alerting response to a salient stimulus. The comparable behavioral effects of clonidine and scopolamine are consistent with animal studies indicating close interactions between the noradrenergic and cholinergic neuromodulator systems.
    Psychopharmacology 10/2015; DOI:10.1007/s00213-015-4111-y · 3.88 Impact Factor
Show more