A Comparison of Centroid Tracking and Image Phase for Improved Optokinetic Nystagmus Detection

Optokinetic nystagmus (OKN) is an involuntary sawtooth eye movement that occurs in the presence of a drifting stimulus. Our experience is that low-amplitude/short-duration OKN can challenge the limits of our commercially available Pupil Neon eye-tracker, leading to false negative OKN detection results. We sought to investigate whether such instances could be remediated. We compared automated OKN detection using: (1) the gaze signal from the Pupil Neon (OKN-G), (2) centroid tracking (OKN-C), and (3) an image-phase-based "motion microscopy" technique (OKN-MMIC). The OKN-C and OKN-MMIC methods were also tested as a remediated step after a negative OKN-G result (OKN-C-STEP, OKN-MMIC-STEP). To validate the approaches adults (n = 22) with normal visual acuity was measured whilst viewing trials of an OKN induction stimulus shown at four levels of visibility. Confusion matrices and performance measures were determined for a "main" dataset that included all methods, and a "retest" set, which contained instances where centroid tracking failed. For the main set, all tested methods improved upon OKN-G by Matthew's correlation coefficient (0.80-0.85 vs. 0.76), sensitivity (0.89-0.95 vs. 0.85), and accuracy (0.91-0.93 vs. 0.88); but only OKN-C yielded better specificity (0.90-0.96 vs. 0.95). For the retest set, MMIC and MMIC-STEP methods consistently improved upon the performance of OKN-G across all measures.