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Synchronization markers for Eye tracking experiment

Hello everyone,

I am developing an eye-tracking experiment using Psychopy and a Gazepoint HD eye-tracker. I had a thorough look at the relevant book chapter, the iohub demos & documentation.

I am mainly using the Gazepoint API to send synchronization markers. My task consists of two main routines: in the first one (Search Routine), participants search for an object embedded in naturalistic images and in the second one, they receive feedback whether they found the object or not (Feedback Routine). Initially, I am sending a marker when the trial starts (in the Begin Routine tab of Search Routine), then continuously while participants are searching for the object (Each Frame Tab of Search Routine) and at last when the search has been terminated (End Routine Tab of Search Routine). Additionally, I am sending a continuous marker while feedback is being displayed (Each Frame Tab of Feedback Routine). Among other variables, gazepoint also outputs mouse events (e.g.,left button down, left button up etc.). I would like to have your opinion on the issues below:

  1. Since timing is critical in my experiment, I would like to know whether the sync marker in the Begin Routine Tab literally corresponds (with some acceptable latency) to the start of the trial and the same for the End Routine marker. On other threads in this forum I’ve seen that sometimes routines do not strictly correspond to when things happen, as psychopy “prepeares” stimuli before they are being displayed.
  2. The Search Routine is being terminated after participants perform a left mouse click. However, sometimes when I see the output, the “left_down” mouse event falls within the Search Routine marker (which is good), whereas left mouse up event falls within the Feedback Routine marker. Given that the mouse click terminates the Search Routine is this normal?The difference between left_down and left_up according to the eyetracker’s output can be 80-120 ms. Is this amount sufficient for Psychopy to terminate a routine and start the next one?
  3. Sometimes, the output does not show event markers at all. This happens only for the events in the Begin and End Routine Tabs, which are one-shot event markers and never for the Each Frame or Feedback Routines, which are continuous markers. Is this likely a Psychopy issue or sth on eye-tracker’s side ?

Thanks for your time.