The most common approach to identify brain areas that are active during a specific task is by creating regressors used in a multiple linear regression model (General Linear Model; GLM). BrainVoyager QX uses a text-based file format that, after applying a convolution to the stimulus-based stick- or block functions, stores a set of columns, each representing one of the experimental conditions (or parametric modulations of these) as well as any additional variables added to the model, such as motion parameters, filters, heart-rate or respiratory influences on the hemodynamic BOLD response in the brain.
The information contained in BrainVoyager QX text files is either given in the form:
NameOfField: Value
or, if a short list of values (e.g. an RGB color code triplet) is given, as
NameOfList: Value1 Value2 Value3
or yet, in case several values are to be coded, as an array of values (or strings) without any header
Row1Col1 Row1Col2 Row1Col3 Row2Col1 Row2Col2 Row2Col3 ...
Text-based tokens (constant values) are generally given without quotes, names are given with quotes (with exceptions noted where appropriate)! Linebreaks are added for increased readability. They do, however, not impact the actual reading of information from the file!
FileVersion: 1 NrOfPredictors: 3 NrOfDataPoints: 60 IncludesConstant: 1 FirstConfoundPredictor: 3 255 255 0 0 255 255 255 255 255 "hand" "foot" "Constant" 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.000000 0.000000 1.000000 0.003554 0.000000 1.000000 0.113691 0.000000 1.000000 0.460896 0.000000 1.000000 0.831251 0.000000 1.000000 1.050803 0.000000 1.000000 1.133200 0.000000 1.000000 1.138367 0.000000 1.000000 1.109856 0.000000 1.000000 1.073621 0.000000 1.000000 1.039519 0.000000 1.000000 0.908721 0.000000 1.000000 0.549604 0.003554 1.000000 0.173206 0.113691 1.000000 -0.049103 0.460896 1.000000 -0.132650 0.831251 1.000000 -0.138260 1.050803 1.000000 -0.109856 1.133200 1.000000 -0.073621 1.138367 1.000000 -0.043074 1.109856 1.000000 -0.022412 1.073621 1.000000 -0.010500 1.039519 1.000000 -0.004457 0.908721 1.000000 0.001855 0.549604 1.000000 0.113141 0.173206 1.000000 0.460789 -0.049103 1.000000 0.831251 -0.132650 1.000000 1.050803 -0.138260 1.000000 1.133200 -0.109856 1.000000 1.138367 -0.073621 1.000000 1.109856 -0.043074 1.000000 1.073621 -0.022412 1.000000 1.039519 -0.010500 1.000000 0.908721 -0.004457 1.000000 0.549604 0.001855 1.000000 0.173206 0.113141 1.000000 -0.049103 0.460789 1.000000 -0.132650 0.831251 1.000000 -0.138260 1.050803 1.000000 -0.109856 1.133200 1.000000 -0.073621 1.138367 1.000000 -0.043074 1.109856 1.000000 -0.022412 1.073621 1.000000 -0.010500 1.039519 1.000000 -0.004457 0.908721 1.000000 -0.001700 0.549604 1.000000 -0.000550 0.173206 1.000000 -0.000107 -0.049103 1.000000 0.000000 -0.132650 1.000000 0.000000 -0.138260 1.000000 0.000000 -0.109856 1.000000 0.000000 -0.073621 1.000000
As almost any text-based file format in BrainVoyager QX, a FileVersion field allows the program to add new features. Given that information, the following fields are currently supported by NeuroElf/xff:
| Field name | Type | Content | Meaning |
|---|---|---|---|
| FileVersion | single number | 1 | as the SDM file format has replaced the former RTC file format (which in its most recent form had file version 3), the enumeration restarted at 1 |
| NrOfPredictors | single number | e.g. 3 | specifies the number of columns to be read from the file (equivalent to the number of regressors/predictors used in the regression of one run/session/study |
| NrOfDataPoints | single number | e.g. 60 | specifies the number of rows to be read from the file (equivalent to the number of data/sample/time points that will enter the regression) |
| IncludesConstant | numeric flag | either 0 or 1 | if the regression table contains a column coding the constant (intercept) of the regression equation, this flag must be set to 1; in that case, the constant column should be the last column in the table |
| FirstConfoundPredictor | single number | e.g. 3 | as an enhancement of the SDM over the former RTC format, additional regressors that are of no real interest (such as error trials, motion parameters, etc.) can be added to the model; importantly these regressors can vary across subjects, whereas all non-counfound regressors must match; this number thus tells BrainVoyager just as NeuroElf which regressors should be discarded after performing the actual regression |
| PredictorColors | numeric array of RGB color code triplets | e.g. 255 0 0 0 255 0 | the example gives two RGB colors (red and green); the number of triplets must match the NrOfPredictors field, only integer values in the closed range of 0 through 255 can be used |
| PredictorNames | array of strings | e.g. “p1” “p2” “Constant” | list of strings, each encapsulated in double quotes, representing the names of each of the columns (incl. the confound columns!); number must match the NrOfPredictors field, names should be unique and the name of the last column, if it is the constant/intercept regressor, should be “Constant” |
| SDMMatrix | 2D array of numbers | e.g. see above | this is a tabular format of the regressors with the size NrOfDataPoints by NrOfPredictors; a value of 0 indicates that the condition in question does not have any pull over the regression equation for that data/sample/time point |
In addition to HRF-convolved design matrices, two further applications are given for the SDM format: