Gaze Trajectory Index (GTI): A novel metric to quantify saccade trajectory deviation using eye tracking

Abstract Background Many different indexes have been proposed to quantify saccade curvature based on geometric properties of the saccade trajectory projected on the 2D plane. We introduce the Gaze Trajectory Index (GTI), a novel metric to quantify saccade trajectory deviation based on calculation of the rotational eye movements performed in 3D space while following a 2D saccade trajectory recorded with eye tracking (ET). Methods We provided a description of GTI calculation. In 13 subjects with normal binocular vision we assessed GTI in single-target tests, then we evaluated GTI against previously proposed metrics (Maximum Deviation,MD; Area Curvature,AC; Quadratic Curvature,QC; Initial Direction,ID) using a distractor paradigm that elicited two types of saccade deviations, i.e.“inner-curved” and “outer-curved” saccades. Results In single-target tests GTI showed that saccade curvature was significantly higher for oblique than for vertical saccades (0.86°±0.32 vs 0.55°±0.60,p  Conclusion The novel GTI seems to have adjunctive potential, particularly for outer-curved trajectories, in the estimation of the absolute amount of saccade trajectory deviation.