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Martin Rolfs, Ralf Engbert, Reinhold Kliegl; Perception and motor control: The link between fixational eye movements and postural sway. Journal of Vision 2004;4(8):655. doi: 10.1167/4.8.655.
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During the fixation of a stationary scene, eye position is unperceivably altered by small involuntary eye movements. Two important types of these “fixational” eye movements are drift and microsaccades. In a previous study (Engbert & Kliegl, Psychol. Sci., in press), we tracked eye movements during fixation and investigated statistical behaviour of miniature eye movements using a random-walk analysis. Scaling exponents obtained by this analysis indicated a separation of time scales in fixational eye movements. Here we investigate how microsaccades interact with postural sway in three different conditions: sitting with the head positioned on a chin rest (SIC), normal sitting (SIT), and upright standing (STA). Using the same analysis, we replicate the findings of our first study in the SIC condition: Microsaccades enhance fixation errors on a short time scale, a phenomenon known as persistence, and control fixation errors on a longer time scale (anti-persistence). On the short time scale, scaling exponents are very similar in SIC, SIT, and STA. On the long time scale, less fixation errors can be observed (more anti-persistence), although postural sway contributes to the noise-level in gaze position. The interaction of fixational eye movements with postural control indicate a global coupling of perceptual motor systems. Miniature eye movements constitute visual fixation, the platform on which almost all visual perception depends — understanding their properties has potential impact on fundamental mechanisms of perception.
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