Pygaze wait_for_saccade_end with timeout?

Comments

• sebastiaan

  November 2022

  Hi @kolfers ,

  I would adapt the the wait_for_event() function from PyGaze to break after a timeout.

  • https://github.com/smathot/PyGaze/blob/master/pygaze/_eyetracker/libeyelink.py#L684

  I blind-coded the example below (I don't have an eye tracker now to test) but it should convey the general idea of how wait for a saccade using the EyeLink's native event detection with a timeout. This script should simply go into an inline_script item.

  import pylink
  
  t0 = clock.get_time()
  saccade = False
  timeout = 2000
  for ms in clock.loop_for(timeout):
      d = pylink.getEYELINK().getNextData()
      if d == pylink.STARTSACC:
          float_data  = pylink.getEYELINK().getFloatData()
          tc = float_data.getTime() - eyetracker._get_eyelink_clock_async()
          if tc > t0:
              saccade = True
              break
  

  One workaround I am currently considering / testing, but seems quite crude is to run wait_for_saccade_end() in a new thread using the threading module, and adding a trace so the thread can be killed if needed

  Threading is generally not a good idea for things like this because the timing is quite unreliable, and it's also easy to create race conditions that unpredictably make your experiment crash!

  — Sebastiaan

  
  
  Check out SigmundAI.eu for our OpenSesame AI assistant!
  
• kolfers

  November 2022

  Hi Sebastiaan,

  Thank you, that approach did the trick. I couldn't get the clock.loop_for to work though. Perhaps because of the imported clock from pygaze.libtime? In case someone else finds it useful in the future:

      def wait_for_event_timeout(self, event, timeout):
  
          """See pygaze._eyetracker.baseeyetracker.BaseEyeTracker"""
  
          if not self.recording:
              raise Exception(
                  "Error in libeyelink.libeyelink.wait_for_event(): Recording "
                  "was not started before collecting eyelink data!")
              
          start_time = clock.get_time()
          check_time = False
          if isinstance(timeout,int) and timeout > 0:
              check_time = True 
              end_time = start_time + timeout
          else:
              raise Exception("timeout (in ms) should be an integer larger than 0")
  
          if self.eye_used == None:
              self.set_eye_used()
          if self.eventdetection == 'native':
              # since the link buffer was not have been polled, old data has
              # accumulated in the buffer -- so ignore events that are old:
              t0 = clock.get_time() # time of call
              while True:
                  if check_time and clock.get_time() >= end_time: return "timeout", clock.get_time
                  d = pylink.getEYELINK().getNextData()
                  if d == event:
                      float_data  = pylink.getEYELINK().getFloatData()
                      # corresponding clock_time
                      tc = float_data.getTime() - self._get_eyelink_clock_async()
                      if tc > t0:
                          return tc, float_data
  
      def wait_for_saccade_start_timeout(self,timeout=None):
  
              """See pygaze._eyetracker.baseeyetracker.BaseEyeTracker"""
              # # # # #
              # EyeLink method
  
              if self.eventdetection == 'native':
                  t,d = self.wait_for_event_timeout(pylink.STARTSACC, timeout)
                  if t == "timeout": return t, None
                  return t, d.getStartGaze()
  
      def wait_for_saccade_end_timeout(self,timeout=None):
  
          """See pygaze._eyetracker.baseeyetracker.BaseEyeTracker"""
  
          # # # # #
          # EyeLink method
  
          if self.eventdetection == 'native':
              t,d = self.wait_for_event_timeout(pylink.ENDSACC,timeout)
              if t == "timeout": return t, None,None
              return t, d.getStartGaze(), d.getEndGaze()