Beyond motion extrapolation: vestibular contribution to head-rotation-induced flash-lag effects

The perceived position of a flash aligned with a moving object usually lags behind that object. This illusion is well known as the flash-lag effect. Interestingly, head rotation alone can also induce a flash-lag effect. To date, the underlying mechanism for the head-rotation-induced flash-lag effect remains unclear. Using a virtual reality approach, we examined the contribution of vestibular signal processing in producing the effect. We found that vestibular, rather than kinesthetic, signal processing is critical for this type of flash-lag effect to occur. When head rotation induced a stationary reference stimulus in space to move on the retina, we observed a flash-lead effect relative to the reference (or a flash-lag effect relative to the head). Moreover, after a short-term adaptation training on a novel association between head rotation and retinal motion, the direction of the flash-lag effect was consistent with the newly trained association. These findings disagree with a previous account extended from the influential motion extrapolation hypothesis. Rather, they support a cross-modal bias hypothesis that the visual-vestibular associations developed from multisensory experiences may generate biasing visual signals in the associated direction with the vestibular signals, which help produce the head-rotation-induced flash-lag effects. Our findings may provide new insight into other multisensory integration phenomena.