Perifoveal spatial compression - a new visual illusion
Space perception of stimuli presented in temporal vsusceptible to large mislocalization. We found a strong compression of space during ocular fixation, whiicinity of a suddenly changing event, such as motion or a saccade eye movement, is ch was induced by the onset of a visual reference presented in the near periphery. A visual reference object was presented followed by a brief whole-field mask. At various times around mask onset a probe dot was flashed. Subjects had to estimate the position of the probe dot in relation to a comparison bar. The probe dot location was perceived nearly veridically when presented long before or after mask onset. However, when the probe dot was presented simultaneously with the mask it appeared shifted toward the reference by as much as 50 percent of their separation. The reference had to appear briefly before mask onset to attract the probe dot. No compression occurred when the reference was presented long before or after the mask. When we presented the probe dot and reference with similar brief durations, the more peripheral stimulus always shifted toward the more foveal stimulus independently of their temporal order. We suggest that the attraction can be explained by the summation of the neural activity distributions of probe and reference. Underlying the observed effect might be a mechanism, which tries to establish spatial continuity of changing objects. The perception of two flashed objects might be attributed to motion, in which case apparent motion is seen, or - if the motion transient is masked - to a single stationary object, in which case attraction tries to reduce the apparent separation.
Demo: Please keep your gaze fixated on the black rectangle and observe the stimuli to the right. You should see a green disk getting surreounded by a red circle. If you fixate your gaze then on the green disk itself you will see that actually two disks are presented. However, the second disk, being shown together with the whole-field texture mask, is compressed to the position of the first disk.
Zimmermann E, Fink G, Cavanagh P. (2013) Perifoveal spatial compression. J Vis. 2013 Apr 22;13(5):21. doi: 10.1167/13.5.21.