A key role of orientation in the coding of visual motion direction

Despite the fundamental importance of visual motion processing, our understanding of how the brain represents basic aspects of motion is incomplete. While it is generally believed that direction is the main representational feature of motion, motion processing is also influenced by non-directional orientation signals that are present in most motion stimuli. Here, we aimed to test whether this non-directional motion axis determines motion perception even when orientation is completely absent from the stimulus. Using stimuli with and without orientation signals, we found that serial dependence in a simple motion direction estimation task was predominantly determined by the orientation of the previous motion stimulus. Moreover, the observed attraction profiles closely matched the characteristic pattern of serial attraction found in orientation perception. Evidently, the sequential integration of motion signals depends solely on the orientation of motion, indicating a fundamental role of non-directional orientation in the coding of visual motion direction.