Motion masking at saccadic speed is largely invariant to motion amplitude

The rapid retinal image shifts imposed by saccadic eye movements routinely escape conscious perception—a phenomenon called saccadic omission. A potential cause of saccadic omission is motion masking, a notable reduction in perceived motion amplitude resulting from brief stationary presentation (for a certain masking duration) of an image before and after its motion. While a prior study (Duyck, Wexler, Castet & Collins, 2018) explored the contribution of masking duration and image content, we investigated the impact of the kinematics of the motion itself. In our simulated saccade paradigm, observers fixated the center of a gray screen. A pink-noise background, with the same average luminance, swiftly appeared, rapidly shifted across the screen, and vanished, remaining stationary for the masking duration before and after the shift. Each noise image was repetitive, ensuring it was identical before and after its motion to remove any static cues to the movement’s amplitude. Masking duration varied from 0 to 320 ms. Observers adjusted an on-screen arrow to indicate perceived amplitude and direction of the image shift. We manipulated motion profile (constant vs. saccade-like), amplitude (6, 12, and 18 dva) and duration (39, 55, or 72 ms, corresponding to the expected durations of saccades of the tested amplitudes). Observers reported shorter amplitudes for saccade-like compared to constant motion profiles. Interestingly, reported motion amplitudes remained largely consistent across the wide range of motion amplitudes and durations tested, even when motion was unmasked. Although motion amplitudes were considerably underestimated at all masking durations, discrimination of motion direction remained intact. Despite unmasked motion leading to larger reported amplitudes, motion direction discrimination was poorest in this condition. This study compellingly demonstrates that motion masking systematically reduces the perceived amplitude of a movement, even for large amplitudes. Furthermore, saccadic velocity profiles enhance this effect possibly contributing to the phenomenon of saccadic omission.