Abstract
As a prominent illusion, the motion aftereffect (MAE) has traditionally been considered a visual phenomenon. Recent neuroimaging work has revealed increased activities in MT+ and decreased activities in vestibular regions during the MAE, supporting the notion of visual-vestibular interaction on the MAE. Since the head had to remain stationary in fMRI experiments, vestibular self-motion signals were absent in those studies. Accordingly, more direct evidence is still lacking in terms of whether and how vestibular signals modulate the MAE. By developing a virtual reality approach, the present study for the first time demonstrates that horizontal head rotation affects the perceived velocity of the MAE. We found that the MAE was predominantly perceived as moving faster when its direction was opposite to the direction of head rotation than when its direction was the same as head rotation. The magnitude of this effect was positively correlated with the velocity of head rotation. Similar result patterns were not observed for the real motion stimuli. Our findings support a 'cross-modal bias' hypothesis that after living in a multisensory environment long-term the brain develops a strong association between signals from the visual and vestibular pathways. Consequently, weak biasing visual signals in the associated direction can spontaneously emerge with the input of vestibular signals in the multisensory brain areas, substantially modulating the illusory visual motion represented in those areas as well. The hypothesis can also be used to explain other multisensory integration phenomena.
Highlights
The motion aftereffect (MAE) is a well-known visual aftereffect in which exposure to motion in one direction causes illusory motion of a static pattern in the opposite direction (Anstis et al, 1998)
Because faster head rotation corresponded to stronger vestibular input signal, and was found here to be correlated with stronger modulation of the perceived velocity of MAE, we propose that the MAE was modulated by the vestibular signal in a more special and efficient way as compared to the real motion
This explanation is in agreement with the notion that the MAE is strongly related to visual–vestibular interaction, and is different from real motion with respect to such interaction
Summary
The motion aftereffect (MAE) is a well-known visual aftereffect in which exposure to motion in one direction causes illusory motion of a static pattern in the opposite direction (Anstis et al, 1998). By using multivariate pattern classification, Hogendoorn and Verstraten further reported that in area MT+, the MAE is encoded differently from real motion in the same perceived direction (Hogendoorn and Verstraten, 2013) The activation of MT+ during the MAE potentially relates the MAE with visual–vestibular interaction (possibly in MSTd) Supporting this notion, recent fMRI work reports two important findings that during the MAE, MST (but not MT/V5) solely activates, and the vestibular core region OP2 (the human homologue of macaque’s PIVC) deactivates (Rühl et al, 2018). All these findings hint that visual–vestibular interactions are related to the MAE. Since the MAE to some extent resembles a certain slow real motion in appearance, we examined the influences of head rotation on the perceived velocity of real motion, and compared those results with the observations for the MAE
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