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performlabrit 05-22-2016 04:40 PM

Post-hoc fixation detection from a noisy eye-tracker signal.
I'm looking for tips! I'm using an eye tracker, and brainstorming an algorithm for detecting if someone is fixating upon a target object. The most straight forward approach would be to cast a "gaze vector" from the camera center into the virtual world, and testing for an intersection of this vector with a target object. The issue is that the "gaze vector" may waver on/off the object between frames, or even be slightly and stably off the object by a few degrees.

Note that this data is going to be collected and analyzed OFF-LINE - so that I can filter the gaze signal and apply some corrections.

The ideal solution would take into account the view-dependent outline of the object projected upon the view plane, rather than relying upon a bounding box / circle. So, it makes sense that one would want to solve this problem after having already performed the perspective projection onto a viewing plane.

So, the solution I'm contemplating is this: for potential fixation targets, create a double. Place it at the same place, in the same orientation, but set alpha to 0 and scale up the size.

Fixations upon the target would be calculated by intersecting the gaze vector with the invisible target object.

Any thoughts / tips?

- gD

performlabrit 05-23-2016 08:13 AM

...another point.
...I should say that the scaling of the invisible target would reflect the threshold for fixation in angular degrees.

The downside to this is that one must set the threshold BEFORE running the simulation. In my experience, thresholds must often be specialized to the individual, and to the characteristics of post-calibration track quality.

I'm happy to chat with any Worldviz guys about this kind of thing! I hope that you guys are considering building this kind of functionality into Vizard itself. Not that many folks seem to be thinking about this yet, but the demand is surely going to increase over the next few years.

Jeff 05-24-2016 04:15 AM

I'll check with our developers for suggestions here.

Catota 11-15-2017 02:58 AM

Any news here?

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