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Screening data for ERP analysis Before averaging, it is important to exclude blocks which are contaminated. Two major sources of contamination, movement artefact and eye blink, may be automatically detected. The include status for each block is shown by the color of the block number, seen at the top of the Multi-block Review (see Review#2). Black means it is included, red means it is excluded. Status may be switched by clicking on the number. In the example below, block 53 is excluded, 54 included, etc. |
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Blocks containing eye blinks are excluded from the average using menu selection Include, Screen blocks. |
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Bad blocks may be automatically excluded by selecting Review menu, Include, Screen blocks. Channels used in the screening process are selected by clicking the indicator number seen to the left of the axis of each trace in the Review. Frontal channels or eye channels, for example, may be used if these were included in the electrode array. In the example shown, all channels except the top two event channels are set to 1 (on), but the event channels must be switched off before screening is performed, as they do not contain EEG data and would cause every block to be |
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excluded. When channels are correctly set, automatic screening is then performed. Channel settings and screening parameter settings are stored in a template file so that processing of subsequent records may automatically use the same settings. |
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Averaging Data may now be averaged, by selecting Review menu, Process, Average. Only included blocks are used in the |
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Zoom in to raw data block 53, shown as excluded because of a blink. |
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