# delicate  Y  position with Eyelink2

**URL:** <https://psychtoolbox.discourse.group/t/delicate-y-position-with-eyelink2/740>\
**Category:** Uncategorized\
**Created:** [August 17, 2004, 5:24pm UTC](https://psychtoolbox.discourse.group/t/delicate-y-position-with-eyelink2/740 "2004-08-17T17:24:21Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Allen\_Ingling](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Allen\_Ingling](https://psychtoolbox.discourse.group/u/Allen_Ingling)\
**Post date:** [August 17, 2004, 5:24pm UTC](https://psychtoolbox.discourse.group/t/delicate-y-position-with-eyelink2/740/1 "2004-08-17T17:24:21Z")

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Hello my name is hagen.  
I work at the bauhaus university in weimar germany. we do some  
research with the Eyelink2 gazetracker. We run our EM-tests with  
matlab(Eyelink&Psychtoolbox) on a win2000 Pc-system and now we have  
some problems with our ouput data. here a little discription. Maybe  
anyone out there knows the problem and can help with a little hint.  
Thanks a lot in advance hagen.  
  
we calibrate our subjects, then present some stimuli at certain  
positions. although during test, the eye positions seem to fit quite  
well with the picture (on the secondmonitor), in our data files, the  
y-values are wrong. they are usually(depends on calibration quality)  
about 60 to 200 pixels too high, (only to high never to low).  
for example: we have a good calibration. we then present a central  
fixation cross (at 640, 512 for our resolution of 1280 \* 1024) which  
allows the next stimulus to appear only if the eyes fixate for a  
certain time on the cross. the next stimulus appears (indicating that the  
cross has been fixated), and the data report as coordinates for the  
central fixation something like 636, 290. i.e., x is o.k., y is too  
small. the phenomenon is the same for all resolutions of the display  
monitor. where are the 200 pixels gone?   
  
I am happy about every little hint. :-)

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<div class="post-metadata">

**Author:** ![Allen\_Ingling](https://avatars.discourse-cdn.com/v4/letter/a/a183cd/32.png) [@Allen\_Ingling](https://psychtoolbox.discourse.group/u/Allen_Ingling)\
**Post date:** [June 7, 2007, 9:13pm UTC](https://psychtoolbox.discourse.group/t/delicate-y-position-with-eyelink2/740/2 "2007-06-07T21:13:30Z")

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Also make sure that you have a similar luminance for the calibration  
and the actual stimuli. Pupil size differences between calibration and  
experiment might result in inacurate measurements.   
Another issue is "Looking down" ! When subjects look down at a  
display, the eyelid covers part of the pupil and results in  
displacement of measured center of the ellips downward. Try to put  
your monitor a little higher, so subjects have to look up a little  
bit, and check if their eyelid actually covers their pupil when they  
look at the lower edge of the display.  
Best,  
Arash  
  
  
--- In [psychtoolbox@yahoogroups.com](mailto:psychtoolbox@yahoogroups.com), "franswcornelissen"  
\<f.w.cornelissen@...\> wrote:  

> \>  
> \> Are you supplying the right coordinates to the operator PC about

your screen?  

> \>   
> \> This normally happens within initeyelinkdefaults routine, but

perhaps you change   

> \> resolution afterwards?  
> \>   
> \> Gr.  
> \> Frans  
> \>   
> \>   
> \> --- In [psychtoolbox@yahoogroups.com](mailto:psychtoolbox@yahoogroups.com), "sojoner\_84" \<sojoner@g...\> wrote:  
> \> \> Hello my name is hagen.  
> \> \> I work at the bauhaus university in weimar germany. we do some  
> \> \> research with the Eyelink2 gazetracker. We run our EM-tests with  
> \> \> matlab(Eyelink&Psychtoolbox) on a win2000 Pc-system and now we have  
> \> \> some problems with our ouput data. here a little discription. Maybe  
> \> \> anyone out there knows the problem and can help with a little hint.  
> \> \> Thanks a lot in advance hagen.  
> \> \>   
> \> \> we calibrate our subjects, then present some stimuli at certain  
> \> \> positions. although during test, the eye positions seem to fit quite  
> \> \> well with the picture (on the secondmonitor), in our data files, the  
> \> \> y-values are wrong. they are usually(depends on calibration quality)  
> \> \> about 60 to 200 pixels too high, (only to high never to low).  
> \> \> for example: we have a good calibration. we then present a central  
> \> \> fixation cross (at 640, 512 for our resolution of 1280 \* 1024) which  
> \> \> allows the next stimulus to appear only if the eyes fixate for a  
> \> \> certain time on the cross. the next stimulus appears (indicating

that the  

> \> \> cross has been fixated), and the data report as coordinates for the  
> \> \> central fixation something like 636, 290. i.e., x is o.k., y is too  
> \> \> small. the phenomenon is the same for all resolutions of the display  
> \> \> monitor. where are the 200 pixels gone?   
> \> \>   
> \> \> I am happy about every little hint. :-)  
> \>