Our work demonstrates a tight link between microsaccades and sensitivity to image motion
As part of our research, we investigate the sensory-motor processes that take place around the time of tiny microsaccades. We designed the experimental paradigm demonstrated in the movie below. In this paradigm, a subject maintained steady gaze fixation on a small white spot in the middle of the display. In the background of the display, a vertical sine wave grating was also present. Whenever the computer detected, in real-time, a tiny microsaccadic eye movement by the subject, the computer triggered a horizontal motion of the sine wave grating (with different time delays). We then observed and analyzed the resulting ocular following eye movements that the subject generated to track the motion of the sine wave grating.
In the first part of the movie below, you will see a copy of the stimulus we used. Later, the camera pans to our experimental GUI showing a real-time representation of the subject’s eye movements. The top part of the GUI (white graph) shows the subject’s eye position as a red cross. As you can see, the subject initially is looking at the center of the display. However, when the stimulus moves, the subject’s eye moves as well (to the right or left) to track the image motion. In the bottom part of the same GUI (the black graphs), the subject’s eye position (top) and eye velocity (bottom) are shown as a function of time. Spikes in eye velocity are saccades and microsaccades. As you can see, the image motion (and hence the ocular following response) is started at different times after microsaccades during steady fixation. We analyzed the speed of the eye as a function of time from microsaccades, and we found a dramatic enhancement soon after these tiny fixational flicks. This suggests that sensitivity to full-field image motion is greatly enhanced after tiny microsaccades. More details about this set of experiments can be found in (Chen & Hafed, 2013).