Flicker distorts visual space constancy

Effects of flicker on space perception were measured by displacing a flickering target during saccadic eye movements. A small target was flickered at 33, 66, 130 or 260 Hz. Using a 2-interval forced-choice design, sensitivity to the displacement was about twice as great when the target was moved in the direction opposite the eye movement as when it was moved in the same direction. This would be expected from a partial breakdown of space constancy--the world should seem to jump in the direction opposite an eye movement. Even if a suppression of displacement detection during saccades prevents this jump from being perceived; it should be easier to detect a target displacement in the direction opposite the eye movement than in the same direction: when movement is opposite, the imposed displacement adds to the illusory displacement, making detection easier. Displacements were more easily detected at lower flicker rates. Results imply that both masking and extraretinal signals are important in suppressing the detectability of target displacements during saccades, and that flicker on video display terminals may distort space perception.