![]() ![]() An ensemble averaging method to enhance the ERPs was defined by. However, since the ERP or evoked potential signals are generally subtle in EEG, averaging of many epochs are needed to make them distinguishable. In evoked potentials, each stimulus produces an evoked potential embedded in EEG. ģ.1 Averaging methods to suppress ERP artifactsĮvent Related Potentials (ERP) are electrical signals generated in response to internal or external events and they are recorded by EEG. It is advantageous to have a reference EOG channel during EEG recording for the cancellation of ocular artifact from EEG activity. The blinking artifact generally has an amplitude much larger than that of the background EEG. Blinks which are attributable to the eyelid moving over the cornea, occurring at intervals of 1-10s, generate a characteristic brief potential of between 0.2 s and 0.4 s duration due to eyelid movement over cornea. The direction of eye movements affects the shape of the EOG waveform while a square-like EOG wave is produced by vertical eye movements and blinks which leads to a spike-shaped waveform. Cornea-retinal dipole movement, retinal dipole movement and eyelid movement are the three main proposed causes of the eye movement related voltage potential. The origin of this contamination is disputable. Eye movements are major sources of contamination of EEG. The most important artifacts in a typical EEG recording are ocular electro-oculogram (EOG) artifacts and muscular (EMG) artifacts.Įlectrical potentials due to eye opening/closure, blinks, eyelid flutter and eye movements propagate over the scalp and produce hostile EOG artifacts in the recorded EEG. On the other hand, internal or physiological artifacts are challenging for researchers because of their inclusion of signal or resemblance to the signals. External artifacts can be prevented by proper shielding, grounding cables, isolating and moving cables away from recording sites since they act as antennas during operation. Artifact types and sources are listed in the Table 1. EEG can be contaminated in frequency or time domain by artifacts that are resulted from internal sources of physiologic activities and movement of the subject and/or external sources of environmental interferences, equipment, movement of electrodes and cables. Artifacts are undesired signals that may introduce changes in the measurements and affect the signal of interest. The EEG recording environment and subject related electrical activities during recording deteriorate the signal quality. This work aims to inform the researchers working in the field of EEG about the artifacts and artifact management options available in order to increase the awareness of the available tools such as EEG preprocessing pipelines. They still use the traditional visual inspection of the EEG. ![]() However, the developed methods are not well known by the real practitioners of EEG as a tool because of their limited knowledge about these engineering approaches. Many researchers from various fields studied this challenging phenomenon and came up with some solutions. Therefore, an effective management of these inevitable artifacts is critical for the EEG based researches. For both resting state EEG and ERP studies, artifact handling needs to be carefully carried out in order to retain the maximal signal. Internal artifacts are difficult to detect and remove, because they contain signal information as well. The most common internal artifacts are ocular or muscular origins. Artifacts can be categorized as internal/physiological or external/non-physiological. While some artifacts are avoidable, due to the nature of the EEG techniques there are inevitable artifacts as well. ![]() Among these, the major obstacles are the artifacts. There are various obstacles in the way of use of EEG. ![]()
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