Iohub eye-tracking function

Coding
1

Hello,

I’ve successfully used the following eye-tracking code (iohub) to check coordinates, only in the past I called the ‘check_eyes’ code within each trial itself for each stimuli (greatly expanding my code). When I try to call it from a function outside of my main experiment loop, I get the error ‘global name ‘EventConstants’ is not defined’. I have set EventConstants as a global variable, but I cannot think of any other way to fix this. I have condensed the problem to the small bit of code below to illustrate what gives me this error.

from psychopy.iohub.client import launchHubServer

    window = visual.Window(fullscr=True,color=("black"), allowGUI=True, monitor='testMonitor', units='deg')

    gaze_ok_region = visual.Circle(window, radius=120, units='pix')

    runtime_settings = dict()
    runtime_settings['sampling_rate'] = 500
    runtime_settings['track_eyes'] = 'RIGHT'
    iohub_config = {'eyetracker.hw.sr_research.eyelink.EyeTracker':
                    {'name': 'tracker',
                     #'simulation_mode': True,
                     'model_name': 'EYELINK 1000 DESKTOP',
                     'runtime_settings': runtime_settings
                     },
                    }
                   
    io = launchHubServer(**iohub_config) 

    keyboard = io.devices.keyboard
    display = io.devices.display
    tracker = io.devices.tracker

    def check_eyes():                      #check eye positions & give feedback if wrong
        # get eye sample & check correct position
        global eyes3, EventConstants
        eye_samples = tracker.getEvents(EventConstants.MONOCULAR_EYE_SAMPLE)
        for es in eye_samples:
            if es.status == 0:
                gpos = es.gaze_x, es.gaze_y
            else:
                gpos=None
            if not isinstance(gpos, (tuple, list)):
                pass
            elif  gaze_ok_region.contains(gpos):
                pass
            else:
                eyes3 = "0"
                warning_beep.play()
                break
               
    def trial():
        global eyes3, EventConstants
        check_eyes()
       
    trial()

I have no eye-tracker here, but this should work regardless, and indeed it does work if I remove the ‘check_eyes’ code from the function and paste it right into my main experiment loop. If I could call it from a function each time I wanted it, I could shave a lot of code from my main loop.

Cheers,
Steve

2

In the code you included, I don’t see anywhere where EventConstants is actually declared/assigned: You’ve told your functions it’s a global variable, but it needs to be given a value either with an assignment (EventConstants = something), or, more likely in this case, you’re missing an import.

If I remember correctly, you need to add this line after your first import:

from psychopy.iohub.constants import EventConstants

And then after that, you won’t actually need to use the ‘global’ statement before EventConstants.

The whole ‘The global variable “whatevs” can not be found’ is a little misleading, in that you could take it to mean your variable should be global. What that error actually means in most cases is that the variable was never given a value or doesn’t exist, global or otherwise. Hopefully I’m making sense.

1 Like
3

Oh yes I see. You’re right, the global variable here was misleading. Thanks for your clear response, it helped a lot; it didn’t occur to me that I might have been missing an import. Strange how I don’t need to import ‘EventConstants’ if I’m running the code directly in the experiment routine on a frame by frame basis. The import did fix the issue though.

4

Glad that worked! As to whether it’s imported in the original script, maybe there’s some type of wildcard import like this?:

from psychopy.iohub.constants import *