Group ERP Analysis

This pipeline allows you to markers of interest and generate averaged ERP plots averaged across multiple records submitted.

Slew limit

You can set a slew rate limit to control the EEG signals between successive samples, up to a maximum value. Large voltage step changes from one sample to the next sometimes occur due to electrostatic discharge from the subject (participant), headset movements, or other artifacts. The effect of voltage step changes on filtered signals, and fast Fourier transform (FFT) epochs can artificially persist for a long time after the event. Setting a maximum slew rate limits the extent of step changes and reduces its impact without significantly affecting the EEG signal components. The default slew rate in Analyzer is 30 microvolts. However, you can enter any positive value here.

Referencing

The data processed by Analyzer can be referenced to an aggregate of all the data selected. The available aggregate functions are:

• Mean

• Median

• Interquartile mean

• None (deactivates re-referencing)

Filter Coefficients

Default values are set for you. However, you can change these values if you want to.

If you do not know what you are doing, please use the default values. The default values are shown below.

Target Markers

For ERP analysis, you can add one or more target markers.

First you must give your target marker(s) a name. Then you must select either Value or Label:

• If you select Value, you must input a numerical value.

• If you select Label, you must input a description, like ‘high’.

The marker label/values can be found in your interval marker file when export a record using EmotivPRO.

By clicking on the + icon you can add more target markers. You can delete a target marker by clicking on the trash bin icon next to it.

Time Before and Time After (Epoch)

Time Before, also known as pre event baseline allows you to input a period before the onset of your event. Time after, indicates the period after the onset of your event that you want to analyze.

Once you’ve input the ranges you need for ERP analysis, click on Start.

Plot specifications

Next you can specify whether or not to include the standard error of the mean in your plots.

Results

While your data is processing, the job management page will open. You can download your results file when the job is complete. This pipeline will output a plot of ERPs for each sensor as below:

The pipeline will also output two .csv files:

1. *_plot_data.csv

This file gives you values used to make the averaged ERP plots. Each column description is as below:

marker_name	The epoch time in seconds (x axis in plot).	The EEG amplitude in µV averaged across the number (count) of epochs/events	The standard error of the mean at this time point	Indicates the number of epochs/events averaged for this channel
marker_name	time	eeg.af3	eeg.af3	eeg.af3
		nanmean	stderr	count
Standard	-0.203125	0.113473122	1.496846508	250
Standard	0	0.677394078	1.603492468	250
Standard	0.0078125	0.655782924	1.667573427	250

2. *subject_id.csv

This file gives your the EEG amplitude in µV for all epochs/trials prior to averaging.

The specified marker name	The specified marker value	The Epoched time in seconds	The onset timestamp of the event for this epoch (in unix time)	subject_id	The record ID	The EEG amplitude for each sensory in µV	The EEG amplitude for each sensory in µV
marker_name	marker_value	time	marker_time	subject_id	record_id	eeg.af3	eeg.f7
Standard	A	-0.203125	1664861201	135960	35c23943-d75d-49d2-843a-90ad0b1d7b85	-7.90581484
Standard	A	-0.1953125	1664861201	135960	35c23943-d75d-49d2-843a-90ad0b1d7b85		8.27903705

In both .csv files the time column is epoched/event time. Zero indicates the onset of the event/marker specified. Negative(-) values indicate pre-event baseline period and positive (+) values indicate the time after the onset of the event.