People are often surprised to learn that their eyes never stop moving, even when they fixate on something. It is even more surprising that if our eyes did stop moving, we would become blind to stationary objects due to a brain process called "neural adaptation". This gives rise to a central paradox in visual neuroscience: When we fix our gaze, we produce small eye movements several times each second, of which we are unaware, but without which we would miss much of what is right in front of our face. Further, since we fixate our gaze about 80% of the time, fixational eye movements are responsible for driving most of our visual experience. The physiology and perception of fixational eye movements are therefore critical to understanding the neural mechanisms that overcome neural adaptation and maintain visual awareness. Given that these movements are large enough that we should easily notice them, it is a mystery why the visual world remains perceptually stable during fixation. The process that removes such displacements from our perception is called "microsaccadic suppression". (A saccade is a large shift in eye position.) However, we don't currently know whether the microsaccades are present for the purposes of vision or for the needs of the motor system. With support from the National Science Foundation, Dr. Susana Martinez-Conde and colleagues at the Barrow Neurological Institute will address this gap in knowledge by recording the neural activity in visual brain areas, while subjects view various visual stimuli. To determine the role of motor system inputs in microsaccadic suppression, the project will compare the neural activity caused by microsaccades to the activity induced by stimulus motions that mimic microsaccades. The project will also examine the neural activity that occurs during a visual illusion in which microsaccadic suppression is foiled, called "visual jitter".
Because much of our visual experience occurs during fixation, defining the mechanisms responsible for producing stable perception from a moving eye is a basic issue that will affect our understanding of the entire visual process. The proposed research will identify the contributions of visual versus motor mechanisms in microsaccadic suppression and localize their effects along the visual hierarchy. The funding from this application will be used to support a new research group at the Barrow Neurological Institute which can provide training opportunities in neuroscience for undergraduate, graduate and post-doctoral researchers. It will broadly disseminate results through publications to scientific as well as lay audiences, thus enhancing scientific understanding by the public.
