Small step tracking: implications for the oculomotor "dead zone".

Abstract The apparent contradiction between the sensitivity of the oculomotor system to small errors during maintained fixation of a stationary target and its insensitivity to much larger errors during small step tracking reported by Rashbass (1961) was resolved in this paper by using the contact lens optical lever technique to study the manner in which the oculomotor system responds to small step displacements of the fixation target. Subjects did, without prior practice, use saccades to correct step displacements of the fixation target just as they correct small position errors during maintained fixation: they consistently (>98 per cent) and accurately (to within 0.5′) tracked target steps ranging from 3.4 to 13.8′.