Unconscious perception of a flash can trigger line motion illusion.

When a flash of light precedes a static line segment, an illusory motion sensation is observed with the line propagating away from the flash's location towards the opposite side (Hikosaka et al. in Vision Res 33:1219-1240, 1993). Here we report that a similar illusory motion percept can be triggered by a non-consciously perceived flash. Observers reported illusory line motion (ILM) arising from the flash's location when a stationary line was presented and the flash was not detected. The results imply that the line motion illusion does not depend on conscious awareness of the flash and suggest that processing of unconscious information can modulate the responses of the neural mechanisms involved in motion perception.