Visual jitter inhibits roll vection for an upright observer

It is widely known that visual jitter convoluted with an expanding optical flow can robustly enhance an observer's illusory perception of forward self-motion (eg Palmisano et al 2000 Perception 29 57-67). In the present investigation I examine the effects of visual jitter on visually induced self-rotation (roll vection). The results showed that the strength of roll vection was decreased under conditions where the visual jitter was convoluted into the rotating visual stimulus. Although the extent of the decrement differed according to the amplitude and direction of the jitter, visual jitters in any direction with any amplitude can significantly reduce vection strength, at least under the conditions examined in the present experiment. The perceptual process underlying jitter effects on vection is discussed in the context of visuo-vestibular conflict in perception of self-motion.