Obtaining a quantitative measure of eye movements in human infants: a method of calibrating the electrooculogram.

We have developed a calibration procedure that combines the measurement of the EOG voltage with the concurrent assessment of the actual direction of gaze as revealed by the corneal reflection of a target light. Using this method, we have been able to calibrate the eye-position signal recorded from 2- and 3-month-old infants. Our results show that in young infants (1) the EOG is linearly related to eye position to at least +/- 20 deg; (2) the slopes of the calibration lines measured early and late in the same test session were not significantly different at the 0.1 level; (3) at the most eccentric eye position, the calibration was accurate to within +/- 1 deg; and (4) an abbreviated calibration at 0 and +/- 15 deg, which took less than 2 min, produced essentially the same slope (t-test not significant at the 0.1 level) as a longer procedure that tested at every 5 deg between +20 and -20 deg.