Calibration

- Overview and credits

- How to install the toolbox

- Stereoscopic Calibration

- Code explanation

- Device Evaluation

- Experimental Suite

Monocular vs Binocular Calibration

When a subject is binocularly fixating, the dominant eye is pointing towards the intended target more accurately and precisely than the non-dominant one, which ends up contributing more to fixation disparity. To further complicate matters, eye dominance depends on gaze angle, so which eye will be more accurate changes as a function of where an observer is looking. In order to take these considerations into account, we implemented two separate calibration routines:
a standard calibration procedure and a stereoscopic calibration procedure.

Standard Calibration Procedure
This procedure is executed on a set of terget defined by the user. The targets are presented simultaneously to both eyes.

Stereoscopic Calibration Procedure
As for the standard procedure, this procedure is executed on a set of terget defined by the user. Differently, it is composed by two separate monocular procedures one for the left and one right eye. This allows avoiding the fixation bias due to various factors, like fixation disparity, binocular fusion, etc... Moreover, the last release of the Toobox (3.1), exploiting the capabilities for stereo vision of the Psychotoolbox, provides the explicit functions that allows quick and easy execution of the stereoscopic calibration. With the novel CalibrationStereoProcedure(), the visual targets are presented first to one eye and then to the other.

The accompaing paper clearly shows the different results obtained by the two calibrations, clearly evidencing how if the performance of the two eyes has to be evaluated separately, it is mandatory to perform a stereoscopic calibration. Besideds, if the gaze data are considered together, e.g. to track the gaze direction on a screen, the standard calibration is more suited to the task

The Tobii EyeX Engine provides a nine point calibration procedure in which the calibration points are positioned in the center of the screen, in the four corners, and at the four arms of a cross. The proposed calibration procedure relies on a set of 13 points. With respect to the native Tobii nine point calibration procedure, four targets have been added in order to provide a finer coverage of the screen, which also allows us to evaluate the residual calibration error with greater spatial resolution.