Microsaccades are triggered by low retinal image slip.
Even during visual fixation of a stationary target, our eyes perform rather erratic miniature movements, which represent a random walk. These "fixational" eye movements counteract perceptual fading, a consequence of fast adaptation of the retinal receptor systems to constant input. The most important contribution to fixational eye movements is produced by microsaccades; however, a specific function of microsaccades only recently has been found. Here we show that the occurrence of microsaccades is correlated with low retinal image slip approximately 200 ms before microsaccade onset. This result suggests that microsaccades are triggered dynamically, in contrast to the current view that microsaccades are randomly distributed in time characterized by their rate-of-occurrence of 1 to 2 per second. As a result of the dynamic triggering mechanism, individual microsaccade rate can be predicted by the fractal dimension of trajectories. Finally, we propose a minimal computational model for the dynamic triggering of microsaccades.
Engbert
Ralf
R
Department of Psychology and Helmholtz Center for Mind and Brain Dynamics, University of Potsdam, P.O. Box 60 15 53, 14415 Potsdam, Germany. engbert@uni-potsdam.de
Mergenthaler
Konstantin
K
D000465:Algorithms; D005403:Fixation, Ocular / Q000502:physiology*; D017709:Fractals; D006801:Humans; D008954:Models, Biological; D012160:Retina / Q000378:metabolism*; D012438:Saccades / Q000502:physiology*; D013997:Time Factors; D014796:Visual Perception / Q000502:physiology*