The effect of structured background on smooth pursuit with real and simulated central scotoma

The purpose of the study was to better understand the role of the fovea in smooth pursuit eye movements in human subjects. The research entailed a systematical study of a previously unstudied condition where the foveal inputs of both the background and the pursuit target were eliminated through simulation but the anatomic fovea was intact; and a comprehensive study of smooth pursuit eye movements of human subjects with real central scotoma.;Ten normally sighted subjects (NS) and three central scotoma subjects (CS) were asked to visually pursuit a 0.87o yellow dot moving along either a horizontal or a vertical trajectory against a uniform grey or a binary random checkerboard structured background. The time-position waveform of the target was a sinewave with a 10° amplitude and a frequency of either 0.15 or 0.40 Hz. NS tracked the target with the fovea or a 6.3° diameter simulated central scotoma. A high-speed eye tracker was used to track eye movements during pursuit in all subjects and to provide instantaneous gaze position data for implementing a central scotoma in NS subjects. Composite and smooth pursuit gains were obtained from raw eye position data using standard procedures.;A structured background caused a significantly larger proportional reduction in smooth gain when pursued with a simulated scotoma than with full foveal visual input. This was true under all conditions except in the horizontal direction at 0.40 Hz. In CS, the overall smooth gains were lower when pursuing a target on a structured background than a uniform background. When pursuing a target on a structured background, CS had a significantly larger proportional smooth gain reduction than NS with the fovea or a simulated scotoma. This was true in all conditions except in the vertical direction with a 0.15 Hz target.;Our results demonstrate that an anatomically intact fovea is required to perform quality smooth pursuit on a structured background even if it receives no visual input. A central scotoma disrupts the oculomotor control of smooth pursuit more profoundly than simply cutting off foveal visual inputs.;Keywords: smooth pursuit, fovea, central scotoma, background...