Automatic detection of camera translation in eye video recordings using multiple methods

Compensating for camera translation in video eye-movement recordings by tracking a representative landmark selected automatically by a genetic algorithm

It is common in oculomotor and vestibular research to use video or still cameras to acquire data on eye movements. Unfortunately, such data are often contaminated by unwanted motion of the face relative to the camera, especially during experiments in dynamic motion environments. We develop a method for estimating the motion of a camera relative to a highly deformable surface, specifically the movement of a camera relative to the face and eyes. A small rectangular region of interest (ROI) on the face is automatically selected and tracked throughout a set of video frames as a measure of vertical camera translation. The specific goal is to present a process based on a genetic algorithm that selects a suitable ROI for tracking: one whose translation within the camera image accurately matches the actual relative motion of the camera. We find that co-correlation, a statistic describing the time series of a large group of ROIs, predicts the accuracy of the ROIs, and can be used to select the best ROI from a group. After the genetic algorithm finds the best ROIs from a group, it uses recombination to form a new generation of ROIs that inherit properties of the ROIs from the previous generation. We show that the algorithm can select an ROI that will estimate camera translation and determine the direction that the eye is looking with an average accuracy of 0.75 degrees , even with camera translations of 2.5mm at a viewing distance of 120 mm, which would cause an error of 11 degrees without correction.

Compensating for camera translation in video eye movement recordings by tracking a landmark selected automatically by a genetic algorithm

We develop a method for accurately estimating the motion of a camera relative to a highly deformable surface, specifically the movement of a camera relative to the eye. A small rectangular landmark is selected and tracked throughout a set of video frames as a measure of vertical camera translation. The specific goal is to present a process based on a genetic algorithm that selects a suitable landmark. We find that co-correlation, a statistic relating the time series of a large population of landmarks, is a robust predictor of the accuracy of the landmarks. This statistic is used to iteratively select the best landmark from the population. At each iteration new landmarks are created that inherit properties of the previous population of landmarks. We show that the algorithm can select a landmark that will estimate camera translation with an accuracy of 1.8 pixels, which means that the direction the eye is looking can be determined with an accuracy of better than 0.6 degrees.