[open] drift check

martijnvk

Hi all,

Is there an easy way to show your own drift check screen instead of just 1 fixation point?

Thanks,

Martijn

sebastiaan

Hi Martijn,

pylink, and therefore also libeyelink which is built on top of it, uses a pretty complicated callback system for drawing things during drift correction, calibration, camera setup, etc. So an easy way? No not really I'm afraid.

What you could do is modify the draw_cal_target() function in libeyelink.eyelink_graphics. This should be doable, but of course it means that you have to create different versions of libeyelink for each type of calibration target. This is a bit messy, but possible.

• https://github.com/smathot/opensesame_eyelink_plugins/blob/master/eyelink_calibrate/libeyelink.py#L1383

Cheers!
Sebastiaan

martijnvk

Thanks for your reply also to my other question, which I used to solve this problem. It turns out that it is relatively easy.

I found the following information in the api user guide:
doDriftCorrect(x, y, draw, allow_setup)

Performs a drift correction before a trial.
Parameters: <x, y>: Position (in pixels) of drift correction target. : If 1, the drift correction will clear the screen to the target background color, draw the target, and clear the screen again when the drift correction is done. If 0, the fixation target must be drawn by the user. : if 1, accesses Setup menu before returning, else aborts drift correction.
Return value 0 if successful, 27 if ‘Esc’ key was pressed to enter Setup menu or abort

My "hack":
I draw my own custom drift check screen (multiple items on the screen), with a duration of 0ms.

Next, I have an inline script with the following information:

import pylink
pylink.getEYELINK().doDriftCorrect(X,Y,0,1)

The important things is that X&Y are in Eyelink coordinates (0,0) is the top left of the screen and not the center. So, if you want to do a drift check at the center, and your resolution is 1024 * 768, you should say:

pylink.getEYELINK().doDriftCorrect(512,384,0,1)

sebastiaan

Ah right, yes. I figured that calling doDriftCorrect() would automatically result in a call to draw_cal_target(). But indeed it doesn't, which makes things a lot easier.

As a small tip, note that doDriftCorrect() can fail, so ideally you would implement this in a loop of the following type:

c.show() # c should be a canvas with the drift target
while not exp.eyelink.drift_correction( (x, y) ):
    exp.eyelink.calibrate()
    c.show()

martijnvk

Thanks for your help!

I have the following problem at the moment: the experiments stops when I press escape during the 'custom' drift check using pylink. Is there a way to temporarily disable the escape key from exiting the experiment, but still to exit the drift check.

Or, alternatively, can I assign another key to escape the experiment, let's say 'e' instead of 'escape', so I can keep using 'escape' for the drift check without exiting the experiment.

Thanks,

Martijn

sebastiaan

Hi Martijn,

You could catch the exception thrown by pylink.getEYELINK().doDriftCorrect() through a try ... except ... statement. However, the script I posted above already does this (thanks to @Wouter actually). so I would just use this libeyelink functionality.

Cheers!
Sebastiaan

martijnvk

Hi Sebastiaan,

Thanks again for your help. Unfortunately I didn't completely understand your suggestion. So, I'm afraid I need a bit more help here. I tried the following, but this didn't work:

import pylink

c.show() # c should be a canvas with the drift target
while not pylink.getEYELINK().doDriftCorrect(512,384,0,1)
    exp.eyelink.calibrate()
    c.show()

Pressing escape (both on the opensesame and eyelink keyboard) still results in exiting the program. Should I try to change the while statement into this?

while not pylink.getEYELINK().doDriftCorrect(512,384,0,1)==27

(api user guide: Return value 0 if successful, 27 if ‘Esc’ key was pressed to enter Setup menu or abort)

martijnvk

Hi Sebastiaan,

Just in general: can one disable escape to quit the experiment?

Thanks,

Martijn

sebastiaan

Well, this is a bit of a spot-the-differences situation! You are using PyLink's doDriftCorrect(), whereas my example uses libeyelink's drift_correction(). This last function captures the Escape press.

Just in general: can one disable escape to quit the experiment?

No, that's hard-wired for the moment, although it is a question that occasionally comes up and is open for revision.