# Processed data ## Metadata * `session_info.csv`: table with session number, tDCS polarity, date, day of the week and time of each session. * `subject_info.csv`: table with session order, gender, age, and eye dominance of each participant. _See the main `sacc-tDCS` R notebook for more information on each column in these tables_ ## Questionnaire data * `PANAS.csv`: tabular data from the Positive and Negative Affect Scale (Watson et al., 1988). The actual questionnaire is not included, but the instructions, items and scoring we used are reported [here][PANAS]. For Dutch participants, we used a [Dutch-language version][dutch-PANAS] (Engelen et al., 2006). The questionnaire was administered twice in each session, at the beginning and at the end. * `reflection.csv`: data from the questionnaire administered at the end of the second session, included in the `questionnaires` folder in the `doc` component. These are not the raw responses to the questions---those can be found in the scans of the pen-and-paper questionnaires (not available online). Instead, they are categorized versions of the responses. * _session.order_: same as in `subject_info.csv`. * _goal.correct_: response to question 1; whether participant was aware that the experiment was about influencing eye movements with tDCS. Either "yes" or "no". * _session.diff.sensations_: response to question 2; whether participant felt a difference in tDCS-induced sensations between the two sessions. Either "yes" or "no". * _performance.improvement.session.1_ & _performance.improvement.session.2_: response to question 3; whether participant thought their task performance changed in each session. Either "better", "worse", or "none". * _prior.tDCS.experience_: response to question 4; whether participant had been in a tDCS study before. Either "yes" or "no". * `tdcs_sensations.csv`: data from the tDCS side effects questionnaire administered at the end each session, included in the `questionnaires` folder in the `doc` component (see the questionnaire for explanations of each item). _See the `questionnaires` R notebook in the `Notebooks` component for analysis of data from the "PANAS" and "tDCS sensations" questionnaires_ [PANAS]: http://booksite.elsevier.com/9780123745170/Chapter%203/Chapter_3_Worksheet_3.1.pdf [dutch-PANAS]: http://www.ekgp.ugent.be/pages/nl/vragenlijsten/PANAS.pdf ### References Watson, D., Clark, L. A., & Tellegen, A. (1988). Development and validation of brief measures of positive and negative affect: the PANAS scales. Journal of personality and social psychology, 54(6), 1063. Engelen, U., De Peuter, S., Victoir, A., Van Diest, I., & Van den Bergh, O. (2006). Verdere validering van de Positive and Negative Affect Schedule (PANAS) en vergelijking van twee Nederlandstalige versies. gedrag en gezondheid, 34(2), 61-70. ## Frontal eye field data * `FEF_coords_native.csv`: X,Y, and Z coordinates of the frontal eye field for each participant, in native scan space. * `FEF_coords_MNI.csv`: X,Y, and Z coordinates of the frontal eye field for each participant, in MNI space. * `FEF_coords_MNI_excl.csv`: same as `FEF_coords_MNI.csv`, but contains only rows of participants that were included in the data analysis. * `FEF_coords.csv`: contains both native and MNI coordinates. * `FEF.node`: is output from `src/plot_coords.m` in the `Code` component and contains the MNI coordinates in a format such that they can be plotted with [Surf Ice software][surfice] [surfice]: https://www.nitrc.org/projects/surfice/ Only `FEF_coords.csv` has been made available, because the other three contain two additional columns with the folder and scan names of the MRI data, which have the initials of some of the participants. The actual MRI data have also not been made available, because they were acquired prior to this study and thus belong to other researchers. _See the `frontal_eye_field` R notebook in the `Notebooks` component for analysis of the MRI data, and the `Neuronav` component for notes on how the coordinates were determined_ ## Eye tracking data * `sacc-tDCS_data.csv` is output from `analysis.m` in the `src` component and contains the processed eye data for all participants. * `sacc-tDCS_quantiles.csv` is output from `notebooks/RT_quantiles.Rmd` in the `src` component, and contains saccade latency decile data. _See the main `sacc-tDCS` R notebook for more information on each column in these tables_ # Task data The unprocessed eye tracking data is contained in separate (zipped) folders for each participant. ## Raw data Each participant has a `/raw` folder that contains the data as they came from the eye tracker, as well as data that came from the task in MATLAB/Psychtoolbox. There are two exceptions to this structure, because of errors made during the data collection: S18 and S27. Both of them have an extra folder inside `/raw` with the original, (erroneous!) data. There is also a `_notes.md` file in `/raw` that describes what went wrong, and how the corrected data files were generated. ### Eye tracker Each participant's `/raw` folder contains the data in Eyelink's proprietary `.edf` format. These can be converted to plain-text using their `edf2asc` binary program (for Windows or Macs), which can be obtained from SR Research directly (see the [Eyelink event data] section). There is one file per task block (~5 min), for 12 blocks per session, over 2 sessions, so 24 files in total. These are named as follows: `"sacc-tDCS"_[participant]_[tDCS]_[phase]_"block"[block_number]_[timestamp].edf`, where: * __[participant]__ is the subject ID, e.g. "S01", "S28" * __[tDCS]__ is the tDCS code that identifies which stimulation (anodal or cathodal) was used in this session. See the `analysis.m` script in the `Code` component or `tDCS_blinding.m` in the `Documents` component for all the possible codes and the key relating them to tDCS polarity). * __[phase]__ whether this block was before ("pre"), during ("tDCS"), or after "post" stimulation. * __[block_number]__ e.g. "4" * __[timestamp]__: yyy-mm-dd_HH-MM-SS timestamp when the data was written to disk. ### Task The `/raw` folder also contains several MATLAB `.mat` files. These were created each time the task was run, so there should be 4 of them: one for each practice and real run of the task, in both sessions. The name of each file has the structure `"sacc-tDCS"_[participant]_[tDCS]_[taskRun].mat` The task run is coded as either "main" or "practice". These files contains three MATLAB variables, each structures with multiple fields: * `xp`: the eXperimental Parameters, such as the screen resolution, the stimulus size, the number of breaks in the task, etc. * `timeStamps`: the required inter-stimulus intervals for each trial, as well as the measured Psychtoolbox timestamps. * `data`: online estimates of saccade latency and accuracy (used for giving feedback during the task) as well as a vector coding for target presentation side. _See the `sacctDCS_Main_ET.m`, `sacctDCS_getParams.m` task scripts in the `task` folder in the `Code` component for more details on all the information contained in these variables_ ## Eyelink event data For each `.edf` file, there is a plain-text `.asc` version with the same file name (see the [Raw data] section), appened with `_-ns` (no sample). The `.asc` files are considerably reduced in size, because they no longer contain the sample data (at 1000 Hz, i.e. for every ms), but only the events parsed online by the EyeLink: fixations, saccades, or blinks. These `.asc` files can be parsed by the `src/processASC.m` function in the `Code` componentto extract the saccade measures. This function is called in the `analysis.m` script in the `Code` component, which creates the `sacc-tDCS_data.csv` file in the `Data` component that is used in all analyses.