Trackloss with Tobii

Comments

• eduard

  March 2019

  Hi Enzo,

  I haven't worked with the Tobii, but I suppose the validity variable is defined per sample. So at a sampling rate of 500Hz, you get every 2ms the information whether a sample was valid or not. During a trial you will have many samples, so you would need to define how many invalid samples would count as a blink or as looking away (There are probably recommendations online). Getting the sample is rather easy. In an `inline_script`, you can call `x,y = exp.pygaze_eyetracker.sample()`, but this will only give you a single sample. To monitor an entire trial, you would have to wrap everything into a (while) loop, including your stimulus presentation. Depending on how feasible that is in terms of your paradigm, it might make more sense to do this offline (during data analysis). So, basically parse the samples into events (saccades, fixations, blinks) and check per trial whether blinks occurred, or whether a fixation lies outside the allowed region.

  Hope this helps,

  
  

  Eudard

  
• nobiles

  April 2019

  Hi Eduard,

  yes, as you suggest, I'm aiming at obtaining validity for each sample.

  Apart from getting the x and y coordinates from tobii through x,y = exp.pygaze_eyetracker.sample(), is possible to import also the value for an extra variable that I think is part of the tobii output, whose name is "validity"? I think that for each sample, the tobii gives back a binary value 0 or 1.

  
  

  thanks,

  enzo
• eduard

  April 2019

  Hi Enzo,

  There might. You can check the github page of Pygaze to find the part in the tobii implementation that handles accessing Tobii information.

  However, if I remember correctly Tobii codes invalid samples as (-1, -1).

  So, it should be easy to define validity yourself, both online during your experiment as well as offline during analysis.

  E.g.

  if sample == (-1,-1): var.validity = 0
  else: var.validity =1
  

  
  

  hope this helps.

  
  

  Eduard