Moving gratings and microsaccades

This paper reports an extended study of anomalous (enhanced) sensitivity to moving gratings in the range of 1-10 cycles per degree, at high temporal frequencies (greater than 20 Hz), i.e., in the high-frequency corner of the spatiotemporal threshold surface. The effect is very robust. All subjects (n = 5) show the effect with moving or flickering gratings and with or without stabilization of the retinal image. After eliminating various types of potential artifacts, the phenomenon was finally attributed to a form of transient destabilization associated with microsaccadic eye movements. In the unstabilized condition, microsaccades and voluntary saccades both interact with the grating motion to produce visible flashes. With image stabilization, the (1-msec) delay of the Purkinje-image eyetracker interacts with these saccades in a way that increases the visibility of the associated flashes. The form of the threshold data suggests that the size of the saccades may vary with the spatial period of the moving grating.