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Andre Kaminiarz, Kerstin Königs, Frank Bremmer; The main sequence of human optokinetic nystagmus. Journal of Vision 2009;9(8):405. doi: 10.1167/9.8.405.
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Optokinetic nystagmus (OKN) is a reflexive eye movement stabilizing the retinal image e.g. during head movements. It consists of two alternating phases: a slow phase in direction of the stimulus motion and a fast phase in the opposite direction. Two kinds of OKN can be distinguished. A stare-nystagmus is observed when subjects view the stimulus passively. If subjects intentionally follow single stimulus elements they perform a look-nystagmus. The functional relationship between the two forms of fast phases (stare vs. look) and various forms of saccades is as of yet unclear. In this study we therefore compared the main sequences of fast phases elicited during stare- and look-nystagmus, as well as those of spontaneous and visually guided (reflexive and voluntary) saccades. Eye movements were recorded at 500 Hz with an infrared eye tracker. Optokinetic eye movements were elicited by a random dot pattern (RDP) moving horizontally at 10°/s. Subjects were either instructed to stare at the screen without following individual dots (stare-nystagmus condition) or to track individual dots (look-nystagmus condition). Spontaneous saccades were recorded while subjects looked at a homogeneous gray screen without any instructions concerning their eye movements. Finally we recorded visually guided (reflexive and voluntary) saccades. A moving RDP with identical properties as in the OKN experiment served as background in this condition. Across subjects, fast-phases during stare-nystagmus had longer durations and lower peak-velocities than fast-phases during look-nystagmus. Similarly, spontaneous saccades lasted longer and had lower peak-velocities than visually guided saccades. This indicates that fast eye movements towards visual targets are faster than those without a visual target. Direct comparison of the main-sequence of fast-phases during look-nystagmus with saccadic main-sequences revealed largest similarities to visually guided as compared to spontaneous saccades. Therefore our data support the notion of a close functional relationship between look-nystagmus and voluntary eye movements.
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