Temporonasal motion projected on the nasal retina underlies expansion–contraction asymmetry in vection

Contracting visual stimuli have been found to induce stronger vection than expanding stimuli. We sought to determine which component of motion underlies the advantage of contraction over expansion in inducing vection. Either the right or left hemi-visual field of an optic flow was presented to either the right or left eye. Our results revealed that without temporonasal motion projected on the nasal retina, vection was weak even with contracting stimuli. Conversely, vection was strong even with expanding stimuli if this type of motion was present. The advantage of contracting stimuli in inducing vection may be caused by anisotropy in processing motion on the nasal retina.