Component and intrinsic motion integrate in 'dancing bar' illusion

We introduce a new illusion that contradicts common assumptions in the field of visual motion perception. When an unoccluded bar moves at certain speeds and oscillates at certain frequencies, the perceived direction of the bar is not predicted by its intrinsic terminators but is biased to move in the direction orthogonal to its orientation. It appears that the veridical terminator motions are integrated with spurious component motion signals, generating an at times complex pattern of motion around an apparently closed loop path. In the absence of oscillation the effect does not occur. Several factors, including optimal angle, speed, and oscillating distance of the bar, are quantified and possible mechanisms are discussed. In a model, we suggest that the effect arises because of the failure to inhibit spurious component motion signals arising from contours that are nearly oriented along the direction of true motion.