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
Attachment: ecal.xml (10.6 KB)
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
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