How to extract eye tracking data by trial ID

Hi there,

I have lots of eye tracking data from a 2 alternate forced choice experiment. In total, 496 trials per participant.

The data are in .asc format, and include MSGs for every forced choice onset. For example:

I would like to extract the data for each 2AFC trial. Such that my ideal data set would include only saccades/fixations/blinks within the 2AFC period, per trial (Trial ID 1 2AFC : Trial ID 496 2AFC).

Whilst i've been able to extract saccade/fixation/etc information using a toolbox, I'm stuck on how to filter the data by trial.

Maybe this can't even be achieved! But would appreciate any insights.

Answer 1

[dpb]

Easiest would be to read the file line-by-line, looking for the magic value and then save data until the next, adding the trial as a variable...

You forgot to attach any usable data for anybody to actually demonstrate, but "air code" would look something like --

fid=fopen('YourFile.Dat');
ID=input('Enter the magic ID to look for, please; ','s')
ID=upper(ID);
pat="MSG"+wildcardPattern+digitsPattern(7)+wildcardPattern+"TRIALID"+wildcardPattern+digitsPattern(1,4)+wildcardPattern+upper(ID);
j=0;                    % the counter
d=[];                   % empty accumulator for data
l=fgetl(fid);
while ~feof(fid)
  if matches(l,pat)
    j=j+1;              % increment counter
    l=fgetl(fid);       % get first data line in section
  end
  try
    d=[d;[j str2double(l)]];  % convert line to data; add trial number and array
    l=fgetl(fid);         % record for next loop
  catch     % presume failure means next section
    % do nothing special, pass on to next test if in wanted section
    l=fgetl(fid);         % record for next loop
  end
end
fid=fclose(fid);

will (hopefully) leave you with the array of values with the trial # as first variable; save as a matrix or convert to a table as desired.

[jlouise2022]

Hi,

Thanks for your insight. Accepted as answer as this may help someone else.

I'm now working with .edf files as they are easier to convert into mat files.