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Do I need an inline script to log fixation coordinates?

Hello everyone,

I've created an experiment with OpenSesame where people have to react to an "X", which appears in different locations, by pressing different keys. Now, I'd like to add an Eyetracker (SMI RED 250) to this experiment to track the coordinates of the fixations.

With OpenSesame's "logger" I can drag and drop all the variables I need like reaction times or errors. But how do I do this with the "pygaze_log" function? Do I have to add a python inline_script to track the fixation coordinates or do I write the variables I need inside the "log message"-window of the pygaze_logger? I tried the "automatically log all variables" option, but it seems that I don't get the coordinates this way.

Thanks in advance for every help.

Greetings

Christian

Comments

  • Hi Christian,


    There's a few things I'd like to clarify to answer your question:

    1) Logging of gaze position to a text file happens automatically between a "start_recording" and a "stop_recording" item. Please use this in your trial sequence to log data during the parts of your experiment that you need data from.

    2) The "pygaze_log" item logs a specific message to your gaze data file. In eye tracking, you would use this to log events in your design. For example, you should log the onset of screen events (e.g. the appearance of an X). If you do not do this, you won't be able to know what stretch of data corresponds to what events during your experiment. (By the way, I would recommend you don't use the "automatically log all variables", but instead log a short and informative message at the start of each trial, containing the trial number and relevant parameters. But that's a personal preference to keep the log files cleaner; it comes at the cost of potentially forgetting to log something important.)

    3) Eye trackers record estimated gaze position and sometimes pupil size. They do not record fixations. There are online algorithms that can detect fixations as they happen, but these are usually focused on speedy over precise performance. I would recommend you only parse your gaze data into "fixations", "saccades", "blinks", and all other categories you might be interested in.

    I'd recommend reading up on eye tracking a bit before starting an experiment. There's a great book called "Eye Tracking : A Comprehensive Guide to Methods and Measures" by Holmqvist, Nystrom, et al. that will guide you through the basics: http://lup.lub.lu.se/record/1852359


    Cheers,

    Edwin

  • Hi Edwin,

    at first, please excuse my late answer. I had a lot of work to do the last few days.

    Thank you for your answer!

    1) I already use the start_recording and stop_recording items in the trial sequences, but the gaze positions are not written to a text file. So I thought that I needed the pygaze_log item to log the positions.

    2) So the gaze positions should be recorded with the start&stop_recording items and I need the pygaze_log item to log messages, which help me to see which positions belong to the logged data?

    3) Thanks for the recommendation of this book. I will take a look at it to get a better understanding of Eyetracking.


    Greetings

    Christian

  • Could you clarfiy whether a text file is generated and does not contain any gaze data, or whether a text file is not generated at all?

  • Hi Edwin,

    Yes, a text file is generated, but it doesn't contain any gaze data. I tried another example experiment, which logged the gaze data, so I think there is a problem with my experiment rather than the eyetracker.

    But on Friday I have the chance to run the experiment with the eyetracker again. Then, I will tell you what data the text file contains and which variables are logged.

    Greetings

    Christian

  • I had to wait until yesterday to work with the eyetracker again.

    So, there are three files which are created after the experiment is finished. At first the file which contais the variables and data obtained through OpenSesame. Then the log file of the eyetracker. The third file is a file without an extension. I found out that you have to add the ".idf"-extension yourself. I did that and then I could open it with "BeGaze" and export all data that the eyetracker had collected.

    So, the problem was that the file didn't have an extension. So I wasn't able to use it or see that it contains the data from the eyetracker.

    Now I'm able to see and analyze the gaze positions within the trial via "BeGaze".

    After the experiment there is also a folder named "subject-(subject-id)_images" which is empty. Is it possible to automatically save pictures of the different stimuli of the test inside this folder? That would be very helpful for the analysis of the gaze positions with "BeGaze".


    Greetings

    Christian

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