This window is dedicated to the viewing and analysis of the computed ERPs in the time domain. It looks like the following:

This window is decorated with a menu, two dedicated toolbars and a 5 pages sidebar (on the left side of the window). The main area shows the ERPs signals in the time domain.

Let’s examine them in details one by one.

The Averages Toolbars

This view provides two specific toolbars, which allow to set the visualization modality and some filtering options.  The first toolbar appears as follows when in Average Mode:

One can set from left to right:

• the montage;
• the averaging modality (Normal Average, Single Trial and Moving Averaging);
• the ERP to be visualized (among all those computed and resident in memory);
• 4 buttons enabled only when Single Trial mode is active (surrounded in the figure by a red line) that allow respectively to superimpose the running average on the single trial, to go to the previous or next trial and to accept or reject every single trial;
• the lock button which forces, if pressed, all main changes (e.g. montage, sensitivity, filtering, etc…) to be applied to all the averages computed and resident in memory;
• the measures button;
• the overlap button that allows to visualize all the channels starting from the same screen position;
• the matrix view selector through which one can set how many ERPs to visualize in a grid like view (by setting the number of rows and columns).

The second toolbar (see figure below), allows to set sensitivity (Sens) and filtering options for the channel(s) described in the leftmost combo box (Chn/Group). One can then set the filter type (IIR, including Zero-Phase, FIR, recursive, etc..), its state through a check like button that indicates if it is enabled or not, the cutoff frequencies of the band pass filter respectively LF, that is the Low Frequency (and not the Low Pass Filter!) and HF,  that is the High Frequency (and not a High Pass Filter!) and a toggle button for enabling (pressed) or disabling (un-pressed) the notch filter.

The Averages Menu

From the Averages Menu one can choose from the following commands:

1. View Averages, to select and set the focus on this window. This command is equivalent to press the Averages button in the main toolbar.
2. Start New Average…, to invoke again the Average Manager form and create a new average (all the previously computed ones are preserved).
3. Edit Average…, to modify an already existing computed average: the Average Builder Form will be invoked and one can change the parameters and recompute the currently selected average;
4. Perform Average, to recompute the average;
5. Enable All Trials, to re-accept all the discarded trials (either automatically or manually);
6. Disable All Trials, to discard all the trials (usually used when one wants to restart to manually build an average from scratch by hand);
7. Select Trials…, to manually accept or discard trials.

       This is useful for example if one wants to quickly  select just a reduced set of trials or need a fine way to accept/discard every single trial. Selecting this will open a form that will show the accepted/rejected status of each trial. It is also possible to select / unselect trials from this list one by one. The list shows, for each trial, its progressive number, the eventual reason for its discarding (an artifact, a trial range such as in the moving averaging modality, or the user manually discarded it), the associated triggering event and the time of its occurrence relative to the beginning of the recording.

1. Copy Average To Clipboard, to copy the raw values of the actually visualized averages to the clipboard. This is the easiest way of exporting the data. Also the Standard Deviations are exported.
2. Copy Single Trial To Clipboard, to copy the currently visualized single trial to the clipboard.
3. Normal View, the default one, in which all the selected traces are visible on the same main frame. In this modality the statistics and the difference among two ERPs can be visualized.

1. Scalp View (the one of figure) in which the ERP is visualized using the 2-D coordinates of the sensors. Each sensor has its own frame. This is useful to easily show differences in evoked responses according to different areas. Also in this viewing modality is possible to see the statistics or the differences among two different ERPs.

1. Channel Grid View, in which each channel is displayed on separate boxes, arranged in a matrix whose size can be freely set (up to 8 rows and 8 columns).

1. Measures, to compute simple values from ERPs (area, delta and amplitude as identified by one or two cursors). This are different with respect to the advanced ERP Measures.
2. Copy Measures to Clipboard, to copy the aforementioned measures to the clipboard.
3. Display, to select which items should be visualized with the ERPs.
4. Colours, to determine the color of the Window and the traces areas.
5. Label Font, to select the font type and size for visualizing the labels. Note that it is scaled according to the window size.

The Averages SideBar

The Averages Sidebar is put on the left part of the main NPX Lab frame, and it is  formed by 5 pages:

1. The Sensors page, which describes the main characteristics of the sensors of the opened file.

       These include the name of the sensor, its type (e.g. EEG, MEG, ICA, EMG, etc..) its class, that is if it is a really acquired channel (Real) or if it was computed or generated by some built-in facility (e.g. the time marker, TM or the Global Field Power, GFP). In this case the sensors are called Virtual. Finally, the SR reports the sampling rate of the data.

1. The Channels page, which allows to set many parameters related to the visualization of the channels (which, in general, are bipolar data obtained after a montage has been selected. E.g. F1-F2, F3-F4, etc...).

       The options that one can set are:

1. The Sensitivity, which reflects a sort of “visual gain” and that is used to visually enlarge or reduce the vertical excursion of the signal.
2. The Colour.
3. The Polarity, where Normal means Negative Up and Inverted means Positive Up.
4. The Rectification, which is useful for example for EMG data and which corresponds to compute the absolute value on the channel.

Furthermore one can choose, for each channel, if it should be visualized or hidden (useful for removing noisy channels from the display).

1. The Events page, which allows to access all the events and the relative functions that operate on them. It is populated by two main Lists: the first (topmost) one shows all the events types and their count, while the second (bottom) all the single instances of the events.

       All the events can be filtered in and out in different ways: the Spot/State checkboxes (top left of the page) allows you to just consider some of them. Then, the checkboxes of the events types list allows to select which event instances should be included in the bottom list. So, for example one would just want to list the events of type Flash (which are of type Spot), the easier (and faster) thing to do is to press the Disable All button, which unchecks all the items in the Events Type list. After this the events instances list should be empty. And then check the corresponding Flash checkbox (there are 1080 of them in the file in the figure). After this, the events instances list will be populated by 1080 items, each of them indicating the begin and end of the occurrence of each event instance.

Two other buttons, the Calculator… and the Advanced… buttons will open the corresponding forms that allow you to create events from already existing ones (there are many very powerful functions in this form) and to review and make some processing on events (e.g. rename, delete, etc…) in a very fine way.

1. The Processors page, which gives you access to all the processors available for that file and their settings.

       From this page you can enable the digital filter parameters (either IIR or FIR), you can define your spatial filtering settings (e.g. Small Laplacian) or you can enable/disable the Independent Component Analysis processors that allows, among others, to remove noise sources like ocular artefacts or power-line noise. Note that in order to use the ICA you need to have a NPX file with already computed ICA weights with the ICA Front End tool, that you can find (if you choose to install it, which is the default option) in the ICA group of your NPX Lab Suite menu (Start | Programs | NPX Lab | ICA | ICA Front End).

1. The ERPs page is probably the most important one because it gives you access to all the main ERP related options of the ERP module. It is grouped in two parts (Main Average, Secondary Average).

       The first one is populated, from top to down, with the following items:

1. Five buttons that allow you to create a new average (New…, which will cause the Average Manager form to appear), delete a computed one (Erase), review the parameters used to compute an average (View…), modify the parameters used to compute and average and recompute it (Edit…) and finally recompute an average, needed when some changes (e.g. filtering) were made (Process).
2. A list view, which shows all the computed Averages, their colour and number of trial (accepted and total).
3. A short memo box, which shows the main macro parameters used to compute the average selected from the above list.
4. A small box which indicates the averaging modality (Single Trial, Normal, Moving Average).
5. A button which allows to select “by hand” which trials to include in the average computation (which will make the “Single Trials Selection Box” described in the Averages Menu section to appear).

The Secondary Average group, instead, is used for the comparison of two averages, the one selected from the Main Average list and the one selected in the list of this group. Note that in this latter list only those averages that are “compatible” with the main average are displayed, that is only those who have been segmented with the same pre-triggering and duration time. If one wants to make a comparison of Targets and Non Targets ERPs in a P300 protocols, for example, then he should generate two averages with same pre-triggering and duration times and then select one of these from the Main Average list and the other from the Secondary Average list. The two averages will be then shown one over the other as in the right figure. Then, it will be possible to check the “Show t-test” and/or the “Show Difference” checkboxes. They will cause to show in the Averages view the p-values computed from the sample by sample t-test and/or the difference signal (main minus secondary averages) among the two selected averages. In fact, for each sample of each average, not only the mean value is computed, but also its standard deviation, so that each averaged sample actually represents a distribution. Then, it is possible to compare the corresponding samples of two averages because the necessary information to describe its distribution is also computed.

Green bubbles represent the statistical significance of the differences of the two signals: the isolectric line (e.g. 0 microvolts) represents values which are equal to the set threshold value (e.g. p = 0.05 in the figure) and p values greater than the threshold value are NOT displayed. The p = 0 value is set midway between two consecutive isolectric lines, as in the figure.

       

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