Eccentricity dependence of the curveball illusion.

When the Gaussian envelope of a Gabor patch moves straight down while its sine wave component drifts to the left, the Gabor is seen to move down to the left when viewed with peripheral vision (exhibiting the so-called curveball illusion) but straight down when viewed foveally. We used a nulling procedure to quantify the strength of the curveball illusion at a range of stimulus sizes and eccentricities to determine if the illusion is size dependent and whether size scaling can equate the strength of the illusion across the visual field. We find that the illusion is size dependent (illusion strength decreases with increasing stimulus size) but that size scaling is not sufficient to elicit an illusion at fixation that matches the strength of the illusion at 10°. These results suggest that certain changes in motion processing across the visual field differ in more than just the local scale of the mechanisms involved.