TemporalSmoothingFD3D Method


Description

Filters in the frequency domain the time series of each voxel in a VTC file. Can be used to remove linear and non-linear drifts (high-pass) and/or to smooth the time series (low-pass).

Syntax

objDocument.TemporalSmoothingFD3D(intHighPass, intLowPass)

Remarks

Valid only if objDocument is of type VMR and if a VTC file has been linked. If the VTC file is referenced but not in memory, BrainVoyager will load the VTC file prior to running the temporal filter. The high- and low pass values are interpreted in cycles per lenght of the time course measured in volumes. A high pass value of "3" removes frequency components below 3 cycles within the time series. A low pass value equal to or greater than half the length of the time series will have no effect (Nyquist theorem), i.e. the low-pass filter is turned off. If the time series data, for example, contains 256 measurements, then a low pass value of 128 or greater lets everything pass, i.e. it has no effect and is turned off. In the GUI version, BrainVoyager sets the default value of the low pass to one-third of the lenght of the time series which proved to produce good results, i..e. it results in slightly smoothed time serieses. It is, however, recommended, not to use low pass filtering at all when preprocessing data sets from event-related designs. This is also the reason, why low pass filtering is turned off in the GUI version (3D Data Preprocessing dialog).
As in the GUI version, the temporal filter produces a new VTC file which is saved to disk automatically under a new file name. The new file name is based on the name of the linked VTC file prior to starting the filter and adds a substring describing the preprocessing performed. If, for example, the name of the linked VTC file was "cg_objects_SC_3DMC.vtc", the new name will be "cg_objects_SC_3DMC_FTS-3-126.vtc". The added substring "_FTS-3-126" describes that temporal smoothing (TS) has been performed in the frequency domain (FTS) using a high-pass filter of "3" and a low-pass filter of "126". All 3D preprocessing steps add such descriptive substrings which makes it easy to get the information about the sequence of steps which has been performed to produce a particular VTC file. If you do not want to use the implicit naming scheme, you might want to use the method TemporalSmoothingFD3DEx which allows to specify the source VTC file and the target VTC file.
Note also that the resulting VTC file is linked automatically to objDocument which allows to run a cascade of preprocessing commands without having to link intermediate files.

Example

' VBScript
Set doc = BrainVoyager.
OpenDocument("subject.vmr")
doc.
LinkVTC "cg_objects_SC.vtc"
doc.
TemporalSmoothingFD3D 3, 200

// JScript
doc = BrainVoyager.
OpenDocument("subject.vmr");
doc.
LinkVTC("cg_objects_SC.vtc");
doc.
TemporalSmoothingFD3D(3, 200);

# PerlScript
$doc = $BrainVoyager->
OpenDocument("subject.vmr");
$doc->
LinkVTC("cg_objects_SC.vtc");
$doc->
TemporalSmoothingFD3D(3, 200);