Interest Areas for Data Analysis

Jenna Duclos

October 25, 2016

Source: vignettes/InterestAreas2.Rmd

Applying Interest Areas in DataViewer

After *.ias files have been created they can be loaded into DataViewer with EyeLink data files (.edf) to help analyze data and generate interest area reports. For each trial in an .edf there should also be one *.ias. If you will be working with multiple trials in an .edf, it is recommended that when you are creating your interest area files in R you save them with a name that can be easily identified and related to corresponding trials in *.edf files in DataViewer. As seen in our examples above, the interest area template for trial 1 was saved as trial1.ias. A cohesive naming scheme across the .edf trial names and interest area templates will simplify the matching process. Also, if you have multiple subjects and will be viewing many .edf files in DataViewer at once, each .edf loaded in a single viewing session must have a different name even if the content of the .edf is different.

I. Interest Areas for Single .edf Files:

  1. Load the .edf in SRR EyeLink DataViewer:

    1. Load EyeLink DataViewer and click File > Import Data… > EyeLink Data File…

    2. Navigate to the directory containing the .edf, select the .edf, and click Load. The .edf will be loaded in DataViewer in the Inspector Data window.

  2. Import the corresponding interest area files for the trials:

    1. Click File > Import Data… > Interest Area Template…

    2. Navigate to directory containing *.ias files, choose all the *.ias files that correspond to the trials in the .edf and and press Load. The *.ias files will be loaded in the Inspector Data window in the Interest Area Templates subfolder.

  3. Match the correct *.ias to the trials:

    1. In the Inspector Data window view all of the trials by expanding the .edf file by pressing +. Then click on the first trial and look at the fields that become available below.

    2. The field labeled Interest Area Set should have a value of Empty Interest Area Set. Select this value and when the drop down menu appears you will see all the *.ias. Select the *.ias that corresponds to the trial you are editing.

    3. Repeat steps 1 & 2 until each trial in the .edf has an *.ias.

    The interest areas should now overlay the eyemovement data in the Trial View window.

    Note: If eye movement data is binocular, before creating Interest Area Reports, toggle between the left and right eye data by selecting Edit > Preferences > General > and checking/unchecking Use Right Eye if Binocular. This will help you are select the eye with the best data across all trials. You can use the EYE_USED variable on your interest area report to specify which eye is used for this subject’s data.

II. Interest Areas for Multiple .edf Files

  1. Load multiple .edfs in DataViewer:

    1. Load EyeLink DataViewer and click File > Import Data… > Multiple EyeLink Data Files…

    2. In Import EyeLink Data File window check the Include Sub-directories box and navigate to the directory containing all .edfs you want to import, then click open.

    3. When the .edfs load check the boxes for the files you want to import and select Import. All files will be loaded in the Inspector Data window and sorted by .edf name.

  2. Import the corresponding interest area files for the trials:

    1. Click File > Import Data… > Interest Area Template…

    2. Navigate to directory containing *.ias files, choose all the *.ias files that correspond to the trials in the .edf and and press Load. The *.ias files will be loaded in the Inspector Data window in the Interest Area Templates subfolder.

  3. Regroup the Inspector window by trial:

    1. Click Edit > Trial Grouping…

    2. In the Available Variables window select your trial label variable (ex. ‘Trial_number’) and press >> to move it to the Selected Variables window and then select Regroup. The Inspector Data window will now be grouped by the trials instead of .edf file names. This means like trials for each .edf will be filed together.

    Note: Regrouping the .edfs by trial is not mandatory, however if .edfs are not grouped by trial, every trial for every .edf loaded will have to have the .ias paired separately. With multiple .edfs and trials this can be very time consuming and tedious.

  4. Match the correct *.ias to the trials:

    1. In the Inspector Data window select a trial number and look at the fields that become available below.

    2. The field labeled Default Interest Area Set should have a value of Empty Interest Area Set. Select this value and when the drop down menu appears select the .ias that corresponds to the trial you are editing.

    3. Repeat steps 1 & 2 until each group of trials has an *.ias.

    Note: If the .edf has not been sorted by trial, refer to the instructions for matching the correct *.ias to the trials for a single .edf file.

Creating Interest Area Reports

Once the interest areas have been specified, DataViewer can be used to generate interest area reports to provide information on various gaze measures for each area. Interest area reports can provide information on fixation count, summed fixation duration, regressions into an interest area, etc. Many variables are available to generate the interest area reports and sets of variables can be exported and imported for easier selection. This is a helpful tool if you will be creating reports with the same variables for many different subjects across many different viewing sessions.

  1. Creating Interest Area Reports:

    1. Click Analysis > Reports > Interest Area Report…

    2. In the Available Variables window select the variables you would like in your report and press >>

      Note: Reference the SRR DataViewer Manual for a complete description of each Interest Area Report Variable.

    3. When all the variables you want are in the Selected Variables window click Next.

    4. Navigate to the folder you want to save your Interest Area Report, name the file, and click Save.

    5. When Save Viewing Session Changes window appears click OK to save the changes made (the Interest Area Report will not save if you do not select OK).

  2. Exporting Interest Area Report Variables:

    1. Click Analysis > Reports > Interest Area Report….

    2. In the Available Variables window select the variables you would like in your report and press >>.

    3. When all the variables you want are in the Selected Variables window click the Export Variable Selection icon below the Selected Variable window.

    4. Click Yes when asked Do you want to save the selection list?

    5. Navigate to a folder, name your report variables, and click Save.

  3. Importing Interest Area Report Variables:

    1. Click Analysis > Reports > Interest Area Report….

    2. Click the Import Variable Selection icon below the Selected Variable window.

    3. Navigate to the folder that contains the interest area report variables that were previously exported (see Exporting Interest Area Report Variables), select the file, click Open.

    4. Proceed with saving the Interest Area Report.

Interest Periods for Data Analysis

For some eye tracking experiments the recording sequences may include more eye movement data than you are actually want to include in the interest area report. Interest Periods can be created to modify the portion of data used in a report.

Example: An experiment requires a subject to read a story orally and then answer a comprehension question. The recording sequence includes the reading of the story and the question, but in Data Viewer we are only interested in viewing the oral reading portion. We can use message events to create Interest Periods that will include only eye movements that occurred during the oral reading portion of the trial (excluding those collected during the comprehension question).

  1. Identify Message Events for an Interest Period:

    1. Load the .edf into a new DataViewer session and expand the expanding the .edf file by pressing +.

    2. Select a trial and then click Toggle Message Event Visibility in the tool bar. In the Inspector window, Message items should be included with the Fixation items.

    3. Identify the message that corresponds to the start of the eye movement data you are interested in viewing.

    Example: For the experiment above we are looking for the message labeled DISPLAY_Story because this message indicates when the story was displayed and the subject began reading.

    1. Identify the message that corresponds to the end of the eye movement data you are interested in viewing.

    Example: For the experiment above we are looking for the message labeled KEYBOARD_End because this message indicates when the experimenter ended the display of the story because the subject finished reading.

  2. Creating the Interest Period:

    1. Click Full Trial Period > Edit > New Interest Period.

    2. In the Label field enter the name for your interest period (ex. Target Story, Target sentence, etc.) and change the End Event Type field from Button Event to Message Event.

    3. Click the Details tab and fill in the Value field with the message that starts your interest period (ex. DISPLAY_Story).

    4. Fill in the End Time Message Text field with the message that ends your interest period (ex. KEYBOARD_End). Press OK and your new Interest Period will appear in the Interest Period Manager window.

    5. Select your new interest period and press OK. All fixations that occurred outside the message events entered will be removed.

    Note: You can switch back to viewing all the eye movement by switching back to the Full Trial Period in the drop down menu. Interest Periods, much like Interest Area report variables, can be exported for future use. This will be helpful if you will be using the same interest periods for many subjects.