FAQ: How can I implement an automatic drift-check?
#1
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 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.

.ebz   Simple_PseudoDriftCheck.ebz (Size: 190.82 KB / Downloads: 49)

At the start of the recording, the DISPLAY_PSEUDO_DRIFTCHECK node presents a Drift Check target in the center of the screen. An Interest Area surrounds the target. This node is followed by an Invisible Boundary Trigger, set to fire if gaze remains within the Interest Area for 500 ms.  A Timer Trigger is wired in parallel, with its Duration property set to 4000 ms. If the Invisible Boundary Trigger fails to fire, the Timer Trigger will fire, and the value of  a "Should_Recalibrate" variable is set to TRUE, and a Recycle Dataline node flags the trial to be recycled.

   

At this point the experimental flow returns to the TRIAL sequence, where a conditional checks the value of the Should_Recalibrate variable, and, if TRUE, links to a DRIFT_CORRECT node. At this point the user can press ESC to get back to the Camera Setup screen and recalibrate if necessary. When done, an Update Attribute node resets the Should_Recalibrate variable to false, and the experiment will continue (with the recycled trial).