A new methodology for determining point-of-gaze in head-mounted eye tracking systems

The ability to determine point-of-gaze with respect to an observed scene provides significant insight into human cognitive processes, since shifts in gaze position are generally guided by shifts in attentional focus. Using a head-mounted eye tracking system, a new methodology based on four or more point correspondences in two views was developed to reconstruct the subject´s point-of-gaze. For exact point correspondences, 95% of the reconstruction errors are less than 0.32° when the homography algorithm with distortion compensation is used to determine gaze position. In a typical visual scanning experiment, 95% of the reconstruction errors are less than 0.90°. Analysis of normalization techniques that reduce the sensitivity of the homography algorithm to input errors suggests that the point correspondences should be arranged in a radially symmetric distribution around the area to be scanned. The new methodology was used in a clinical study on visual selective attention and mood disorders; this study showed that depressed subjects spent significantly more time looking at images with dysphoric themes than normal control subjects.