Eye Link - tracking both eyes

mc7055's Avatar


09 Nov, 2018 08:21 PM

Hi Chris,

To some extend this is a follow up on an older situation that I didn't get fully addressed. EyeLink has the possibility of tracking both eyes simultaneously. In MWorks I have a calibrator that works for each eye (for monocular situations). I would like to have the possibility of recoding the positions of both eyes, while primarily tracking one of them only. Do you see some impediment to this of have some suggestion of how to address it?

Thank you!

  1. Support Staff 1 Posted by Christopher Sta... on 09 Nov, 2018 08:43 PM

    Christopher Stawarz's Avatar

    Hi Mariana,

    No, I don't anticipate any issues with this. You could also track both eyes, if you wanted. You just need to have separate calibrators, filters, and fixation points for each eye you want to track.


  2. 2 Posted by mc7055 on 09 Nov, 2018 10:26 PM

    mc7055's Avatar

    Hi Chris,

    Thank you for the reply.

    I have 2 calibrators, 2 filters, but I am not sure what should be specified
    in the fixation points to specify the eye it should be associated with.
    Would this be set by having different 'trigger_flag'? I've changed it to
    include 2 different 'trigger_flag's (I might only get to test it Monday.)


  3. 3 Posted by mc7055 on 10 Nov, 2018 12:12 AM

    mc7055's Avatar

    Hi Chris,

    I'm sure I'm doing something silly. Not yet working...

    This is how I have the calibrators and filters:

     <calibrators tag="Calibrators">

            <calibrator tag="eyeCalibrator_Right" type="linear_eye_calibrator"
    eyeh_raw="eye_rh_raw" eyev_raw="eye_rv_raw" eyeh_calibrated=
    "eye_h_calibrated" eyev_calibrated="eye_v_calibrated"></calibrator>

            <calibrator tag="eyeCalibrator_Left" type="linear_eye_calibrator"
    eyeh_raw="eye_lh_raw" eyev_raw="eye_lv_raw" eyeh_calibrated=
    "eye_h_calibrated" eyev_calibrated="eye_v_calibrated"></calibrator>


        <filters tag="Filters">

            <filter type="boxcar_filter_1D" in1="eye_v_calibrated" out1="eye_v"
    width_samples="5" tag="eye_v_filter"></filter>

            <filter type="boxcar_filter_1D" in1="eye_h_calibrated" out1="eye_h"
    width_samples="5" tag="eye_h_filter"></filter>

            <filter type="basic_eye_monitor" eyeh_calibrated="eye_h"
    eyev_calibrated="eye_v" eye_state="saccade" width_samples="5"
    saccade_entry_speed="100" saccade_exit_speed="65" tag="saccade detector"


    Thank you,

  4. Support Staff 4 Posted by Christopher Sta... on 13 Nov, 2018 03:03 PM

    Christopher Stawarz's Avatar

    Hi Mariana,

    You're probably running in to trouble here:

    eyeh_calibrated="eye_h_calibrated" eyev_calibrated="eye_v_calibrated"

    Both calibrators write their output to the same two variables (eye_h_calibrated and eye_v_calibrated), so the positions for both eyes are ending up in the same place. That said, this might work if the EyeLink is tracking only one eye at a time (i.e. you've manually selected either the left or right eye, both not both, on the EyeLink PC). Is that what you're doing?

    What I meant by "separate calibrators, filters, and fixation points for each eye" is a full, independent set of variables and components for each eye, e.g.

    linear_eye_calibrator right_eye_calibrator (
        eyeh_raw = right_eye_h_raw
        eyev_raw = right_eye_v_raw
        eyeh_calibrated = right_eye_h_calibrated
        eyev_calibrated = right_eye_v_calibrated
    boxcar_filter_1d (
        in1 = right_eye_h_calibrated
        out1 = right_eye_h
        width_samples = 5
    boxcar_filter_1d (
        in1 = right_eye_v_calibrated
        out1 = right_eye_v
        width_samples = 5
    circular_fixation_point right_eye_fixation_point (
        trigger_width = fixation_width
        trigger_watch_x = right_eye_h
        trigger_watch_y = right_eye_v
        trigger_flag = right_eye_in_window
        color = 1,0,0
        x_size = fixation_point_size
        x_position = fixation_pos_x
        y_position = fixation_pos_y
    basic_eye_monitor (
        eyeh_calibrated = right_eye_h
        eyev_calibrated = right_eye_v
        eye_state = right_eye_saccade
        width_samples = 5
        saccade_entry_speed = 60
        saccade_exit_speed = 20

    and then equivalents for the left eye. This is what you would need to track both eye simultaneously, but maybe that isn't your intent.


  5. 5 Posted by mc7055 on 13 Nov, 2018 03:26 PM

    mc7055's Avatar

    Hi Chris,

    Thank you very much! I'll do that!


  6. 6 Posted by mc7055 on 14 Nov, 2018 06:05 PM

    mc7055's Avatar

    Thank you very much, Chris. I had not separated it well enough at all the
    right/left eye signals. It is working now, thank you!

  7. Support Staff 7 Posted by Christopher Sta... on 14 Nov, 2018 06:36 PM

    Christopher Stawarz's Avatar

    Great! Thanks for letting me know.


  8. Christopher Stawarz closed this discussion on 14 Nov, 2018 06:36 PM.

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