# Fixation point stimulus trigger\_flag updating

**URL:** <https://mworks.discourse.group/t/fixation-point-stimulus-trigger-flag-updating/570>\
**Category:** Support\
**Created:** [July 28, 2014, 3:02pm UTC](https://mworks.discourse.group/t/fixation-point-stimulus-trigger-flag-updating/570 "2014-07-28T15:02:42Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 28, 2014, 3:02pm UTC](https://mworks.discourse.group/t/fixation-point-stimulus-trigger-flag-updating/570/1 "2014-07-28T15:02:42Z")

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Hi Chris,

I’m starting to play with the fixation point stimulus to make a simple saccade program. I’ve noticed that, as expected, the trigger\_flag variable of the stimulus will be updated when I put the trigger watch variables in the window or move them out of the window. However, when I move the fixation point stimulus to a new location, the trigger\_flag variable remains unchanged (so that, if it was 1 before changing locations, it will remain 1 even though I don’t change the watch variables). This seems like undesirable behavior, particularly if one wants to design a smooth pursuit experiment. How is the updating of the trigger\_flag handled?

I’ve attached a file of what I’m working with if that helps clarify the issue. Thanks,  
Seth

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<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 28, 2014, 3:02pm UTC](https://mworks.discourse.group/t/fixation-point-stimulus-trigger-flag-updating/570/2 "2014-07-28T15:02:42Z")

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Attachment: [ecal.xml](https://mworks.discourse.group/uploads/short-url/fzLnZl69O5JqR1IBqqDEKYynFHR.xml) (10.6 KB)

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<div class="post-metadata">

**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 28, 2014, 4:00pm UTC](https://mworks.discourse.group/t/fixation-point-stimulus-trigger-flag-updating/570/3 "2014-07-28T16:00:52Z")

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Hi Seth,

Updates to `trigger_flag` are driven solely by changes in the eye position variables (`eye_x` and `eye_y` in your experiment). This means that changes to the position of the fixation window won’t be taken into account until the next eye position update occurs. While you wouldn’t see this problem as much with real eye data (which is updated continuously), it’d still be possible for you to test `fixOn` before the next eye sample comes in.

I think the right solution here is for your experiment to have two fixation windows: one for the fixation stimulus and one for the target stimulus, each with a different variable for its `trigger_flag`. That way, you won’t have to worry about the timing issues surrounding moving the fixation window.

Also worth noting: I recently added a circular fixation point stimulus, which works identically to the existing fixation point, except that the visible stimulus is an ellipse, and the associated electronic window is a circle. So, in your experiment, you could eliminate `fix_win` and turn `fix` and `target` into circular fixation points, which would simplify things a bit.

Cheers,  
Chris

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**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 28, 2014, 4:31pm UTC](https://mworks.discourse.group/t/fixation-point-stimulus-trigger-flag-updating/570/4 "2014-07-28T16:31:08Z")

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Thanks Chris. I suspected the updates where contingent upon changes in eye position variables, just wanted to confirm. Good tips on simplifying the design.

Cheers,  
Seth

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**Author:** ![cstawarz](https://yyz1.discourse-cdn.com/flex031/user_avatar/mworks.discourse.group/cstawarz/32/3_2.png) [@cstawarz](https://mworks.discourse.group/u/cstawarz)\
**Post date:** [July 19, 2022, 10:58pm UTC](https://mworks.discourse.group/t/fixation-point-stimulus-trigger-flag-updating/570/5 "2022-07-19T22:58:25Z")

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Closed on July 19, 2022, 10:58pm UTC