Par-Files

Paradigm files, or "par-files" are tab-delimited plain-text files that specify to Freesurfer's FS-FAST program when different experimental conditions occurred within each functional run. They have a very straightforward structure, with one line per event or block. The files have between two and four columns according to various sources, though this documentation has changed with different releases of Freesurfer. What seems to work for our release is the following column structure:

Cumulative_Onset     Condition_Number_Code     Duration     Weight

The cumulative onset is specified in seconds and assumes that the first volume onset is at t=0 seconds. If initial volumes have been truncated from the 4D time series, adjust the onsets accordingly, depending on your TR. For example, if your TR is 2 seconds, and you drop the first 4 volumes of a 100-volume series, your resulting data will contain only 96 volumes, and the first event will appear 4*2=8 seconds earlier in the series.

The following is a snippet from a par file for an experiment with a fixed schedule (i.e., all participants had the same experimental timings, rather than a self-paced experiment):

12.000     6     2     1
16.813     3     2     1
21.626     3     2     1
26.038     3     2     1
30.048     3     2     1
34.059     3     2     1
38.470     6     2     1
42.481     4     2     1
46.492     4     2     1
51.305     1     2     1

Here, the experiment starts with the first event happening 12 seconds into the run. It is event condition 6, and the duration of this trial (and all others) is 2 seconds. All trials are given a weight of 1 in the analysis (weights of 0 might be assigned if, for example, you want to discount activity associated with error trials).

An important thing to note: all .par files associated with a particular analysis must have the same filename. This is possible because each .par file is stored in the same directory as the fMRI data that it corresponds to, and the fMRI data for each run is kept in its own directory. For example, you might have the following directory structure:

• FS_T1_501
  • bold
    • 001
      • f.nii
      • booth.par
    • 002
      • f.nii
      • booth.par

When analyzing a fixed-schedule experiment, you should be able to simply copy the appropriate pre-existing par-file for that run from a source directory. For example, the par-files associated with the Booth data can be found in the par_files directory, in subdirectories corresponding with their Reading_Experiment_IDs.

When analyzing data from a self-paced experiment, each participant will have a unique par-file that will have to be generated from his/her MATLAB experimental data file.

Generating Par Files for Self-Paced Experiments

A MATLAB function, FSTSExtractor, has been written to extract the schedule of events from the .mat files generated by our PsychToolBox experiment scripts. Note that the structure of these .mat files is particular to our scripts, and that you shouldn't expect this procedure to work on experiment data files generated by any other means. However, the MATLAB code for this script is provided below and can be modified to accommodate other input data.

FSTSExtractor.m

function stamps=FSTSExtractor(varargin)
%% function stamps=TSExtractor()
% Extract all the timestamps associated with each condition stored in a .mat file.
% These values are saved, but also returned as a vector called stamps (which can be ignored).
% It is assumed that the .mat files are named
% PREFIX_Sub_SUBJECTNUMBER_Run_RUNNUMBER_DD_MMM_YYYY.mat
%
% Mandatory arguments:
%  subject: a string or cell array of strings
%      run: an integer or array of integers
%     date: a serial date number representing a particular date as an
%           integer. This can be created calling the datenum() function. E.g.
%           datenum('19-Nov-2015')
%
% Optional arguments:
%     prefix: a string, such as 'LDT_' that begins your .mat files (default:
%             empty string)
%  directory: a string, such as '/home/experimenter/fmri/data' that contains 
%             your .mat files (default: current working directory) 
%
% Sample usage:
% >> d=datenum('19-Nov-2015');
% >> FSTSExtractor('prefix', 'LDT_', 'subject', 1000, 'run', 1, 'date', d)
% >> FSTSExtractor('prefix', 'LDT_', 'subject', 1001, 'run', 1, 'date', d, ...
%    'directory', '/data/subjects/1001/')
%%
 
% define defaults at the beginning of the code so that you do not need to
% scroll way down in case you want to change something or if the help is
% incomplete
options = struct('prefix',,'subject',, 'run', 0, 'date', datenum(date()), 'directory', pwd() );
 
% read the acceptable names
optionNames = fieldnames(options);

% count arguments
nArgs = length(varargin);
if round(nArgs/2)~=nArgs/2
   error('TSExtractor needs propertyName/propertyValue pairs')
end
 
for pair = reshape(varargin,2,[]) % pair is {propName;propValue}
   inpName = lower(pair{1}); % make case insensitive
   
   if any(strcmp(inpName,optionNames))
       % overwrite options. If you want you can test for the right class here
       % Also, if you find out that there is an option you keep getting wrong,
       % you can use "if strcmp(inpName,'problemOption'),testMore,end"-statements
       options.(inpName) = pair{2};
   else
       error('%s is not a recognized parameter name',inpName)
   end
end

filename = ([options.prefix 'Sub_' num2str(options.subject) '_Run_' num2str(options.run) '_' ... 
datestr(options.date) '.mat']);
s = load([options.directory filesep filename]);
 
writefile=sprintf('Run_%d.par', options.run);
tempts=[s.expinfo.data.timestamp];
tempcn=[s.expinfo.data.conditon];
tempdn=[s.expinfo.data.rt];
tempwt=ones(1,length(tempcn));
%Make sure the condition numbers start at 1.
%If a condition is labeled 0, this is a problem.
%I think 0 is the implicit baseline or something
if(min(tempcn)<1)
 tempcn=tempcn+1;
end
parmatrix=[tempts' double(tempcn') tempdn' tempwt']
dlmwrite(writefile, parmatrix, '\t')
end

Using FSTSExtractor

This function is supposed to be dead-easy to use to create .par files for FreeSurfer. Just follow these three steps:

1. Copy your .mat files from the laptop
2. Run FSTSExtractor in MATLAB
3. Rename your .par files and copy them to the appropriate run directories

Copy Experiment .mat Files

If you have not already done so, copy the relevant .mat experiment files from the experiment laptop. They should be in the /home/experimenter/Documents/MATLAB/Experiments/experimentname/ folder, and follow the naming format convention PREFIX_Sub_SUBJECTNUMBER_Run_RUNNUMBER_DD_MMM_YYYY.mat (e.g., LDT_Sub_1001_Run_1_09_MAY_2016.mat). Place these files in a directory called 'Onsets' within the subject's bold folder, so that the directory tree for that participant looks something like this:

• $SUBJECTS_DIR/
  • SUBJECT_ID/
    • bold/
      • 001/
      • 002/
      • ...
      • 006/
      • Onsets/
        • TestExperiment_Sub_SUBJECT_ID_Run_1_09_MAY_2016.mat
        • TestExperiment_Sub_SUBJECT_ID_Run_2_09_MAY_2016.mat
        • ...
        • TestExperiment_Sub_SUBJECT_ID_Run_6_09_MAY_2016.mat

There should be one .mat file for each run directory (i.e., if your runs are numbered 011 to 016, then there are 6 run directories, and therefore you should have 6 .mat files). If these numbers don't match up, something is very wrong, so stop what you're doing and solve that problem first.

Run FSTSExtractor.m in MATLAB

This function is a MATLAB utility, and so it will need to be in your MATLAB path, and you will have to run it in MATLAB. Navigate to the Onsets/ directory you created and launch MATLAB from your terminal window:

matlab &

The rest of the instructions in this section are carried out in the MATLAB console.

Check to ensure that FSTSExtractor is in your path:

help FSTSExtractor

You should see a bunch of explanatory help text that includes sample usage. If you get an error message saying FSTSExtractor not found, then this function is not in your path. Fix that problem.

Assuming the call for help displayed the program help for FSTSExtractor, use the sample usage as a model for applying it to your new .mat files. When you have run it, you should find you have created a series of Run_??.par files.

Rename and Copy .par files

When you run your GLM, you will specify a single name for the .par file to be used. Thus, all your .par files will have to be assigned the same name. For each of the newly created Run_??.par files, move the file to the corresponding bold/0??/ run directory (e.g., Run_11.par should be copied to the bold/011/ directory). As each file is moved over, rename the file to your chosen name. If other .par files have been created for other participants, you should use whatever name was chosen for those data.

IMPORTANT: The examples above use 'booth.par' as a sample file name. Do not just blindly name everything 'booth.par'! The name of the par-file should be meaningfully related to the experiment they are for!