It has been suggested that the addition of oscillating motion components can facilitate visually induced self-motion perception (vection), even though they generate substantial conflicts between visual and vestibular information about self-motion. In the psychophysical experiments reported here, attributes of sinusoidal oscillation, such as consistency in phases or amplitudes, were varied in order to investigate the perceptual mechanism underlying the facilitative effects of additional oscillation. The results show that coherent oscillation in the orthogonal direction of the main visual motion can facilitate vection strength, whereas variation in the phases or nonuniform amplitude impairs it. Furthermore, the strength of self-motion perception and the perceived rigidity of the visual pattern covaried as a function of stimulus attributes. These results suggest that uniform oscillation first enhances the perceived rigidity of the visual pattern, and then the visual pattern that is perceived as being more rigid induces more compelling self-motion perception.