Event Average
Event average can be done in two ways:
- Method 1: After temporal sorting of components, when you click on
the expanded view of time course and
had selected "Event Average" under "Utilities" menu.
-
Method 2:
Select "Event Average" entry under Utilities drop
down box. This will let you select the data-sets, regressor and component required for the event average.
Event average of ICA time course is calculated based on the onsets of the
selected model time course (See Figure 1). The parameters needed for event
average are window size and interpolation factor (specified in
options window). The procedure for calculating
the event average is given below:
Figure 1: Reference functions used during temporal sorting.

-
The interpolation factor is multiplied with TR (See
SPM design matrix). The ICA time
course is interpolated by the scaled interpolation factor.
-
Onsets of the selected model time course (Sn(1)right_visual_hemisphere*bf(1)
in Figure 1) are used. If the units are in seconds, the selected onsets are
divided by TR.
- Window size is multiplied by the original interpolation factor. Event average
is initialized to zero vector of length equal to the scaled window size.
- Loop is done over the length of the selected onsets.
-
Starting index corresponds to current selected onset value multiplied by
scaled interpolation factor. All the indices from starting index to length of
the scaled window size are used. Time course values of the corresponding
indices are added to the event average.
- Number of onset where ending index exceeds the size of the time course is
determined.
- End of loop over the selected onsets
- Event average is divided by number of onset where index exceeds the size of
the time course.
Figure 2 shows the event averages of the ICA time courses with the defaults from
the expanded view of the ICA time
course. Event averages of the adjusted time courses are shown in figure 3.
Figure 2: Event average of the original ICA time courses with the defaults.

Figure 3: Event average of the adjusted ICA time courses.
