FAQ: How can I implement an automatic drift-check?

[Sam]

During a standard Drift Check procedure, the Host PC software requires manual input to confirm that the drift is acceptable and the trial can proceed. A manual decision is required because any automatic procedure has a high probability of accepting a false positive (e.g. when any 'drift' is actually the result of the participant failing to accurately fixate the target). This would decrease the spatial accuracy of the recorded data. 

If your task involves many short trials, one solution is to skip the Drift Check procedure entirely and replace it with a 'Pseudo Drift Check' within the RECORDING sequence. The attached example illustrates one approach to implementing this in Experiment Builder.

  Simple_PseudoDriftCheck.ebz (Size: 190.82 KB / Downloads: 82)

---

How the "Pseudo Drift Check" Works
This method replaces the manual Drift Check with an automated process inside the RECORDING sequence. Here is a step-by-step breakdown of how the attached example project is configured:

1. Inside the RECORDING seqeunce:
   
      
   
   
   
   1. Present the Target and Define a Fixation Area: At the start of the recording sequence, a DISPLAY_SCREEN ACTION is used to presents a target for the participant to fixate on. An Interest Area is also placed around this target to define the boundaries of a gaze-contingent trigger.
      
   2. Wait for Fixation within the Defined Boundary: An Invisible Boundary Trigger is set to fire only if the participant's gaze remains inside the Interest Area for 500 ms. If this trigger fires, the trial proceeds as normal.
      
   3. Handle Failure to Fixate Within a Time Limit: A Timer Trigger runs in parallel and is set to fire after 4000 ms.
      • If the participant fails to fixate the target within that time, this Timer Trigger will fire.
        
      • This sets a variable named 'Should_Recalibrate' to TRUE.
        
      • It also triggers a Recycle Dataline node, which flags the current trial to be repeated.
        
2. Inside the TRIAL sequence:
   
      
   
   
   1. Check for Recalibration: The experiment flow returns to the main TRIAL sequence.
      • A conditional trigger checks the 'Should_Recalibrate' variable.
        
      • If the variable is TRUE, the experiment jumps to a DRIFT_CORRECT node. At this point, the researcher can press ESC to enter the Camera Setup screen and recalibrate.
        
   2. Reset and Continue: After the drift correction is complete, an Update Attribute node resets the 'Should_Recalibrate' variable back to FALSE. The experiment then continues, starting with the recycled trial.