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  • Title: A method for detecting optokinetic nystagmus based on the optic flow of the limbus.
    Author: Turuwhenua J, Yu TY, Mazharullah Z, Thompson B.
    Journal: Vision Res; 2014 Oct; 103():75-82. PubMed ID: 25151522.
    Abstract:
    Optokinetic nystagmus (OKN) is the sawtooth movement of the eye elicited when an observer views a repeated moving pattern. We present a method for identifying the presence and direction of OKN in recordings of the eye made using a standard off-the-shelf video-camera or webcam. Our approach uses vertical edge detection to determine the limbus/iris boundary, and we estimate the velocity of the edge using Lucas-Kanade optical flow. Heuristic rules are applied to identify saccadic velocity peaks from the resulting velocity signal. The normalized average of the resulting peaks is used to estimate the presence/direction of OKN. Our preliminary testing with six participants observing global motion stimuli with full or partial coherence yields an accuracy of 93% which compares favorably to the performance of an experienced human observer (98% accuracy). Additional tests using high contrast, square-wave gratings show that performance of the technique is consistent at stimulus speeds of 5 and 10deg/s and that OKN is not reported by the algorithm when participants view stationary stimuli.
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