Thesis defense Nynke Niehof (Donders series 431)
14 April 2020
Visuovestibular cue combination in vertical perception
Orientation perception is a fundamental component of many of our interactions with the world. Walking upright would not be possible without a constantly updated sense of which direction is vertical, and of the orientation of our body relative to that vertical. Sensory input about the environment may be delayed, noisy or contradictory. For these reasons, an internal model of orientation becomes useful to provide a percept of orientation that is both immediate and as accurate as possible. It was found here that visuovestibular integration for perceiving vertical is dependent on the task to perform, and the signals available. A visual rotation signal biases the verticality signal generated by the balance system, and thus may be integrated at an early stage, whereas a static visual orientation cue had an independent effect on the perceived vertical. An artificial vestibular angular velocity signal is unaffected by visual rotation, and both of the sensory information sources affect the verticality percept independently when combined. This shows that information from multiple senses is combined in computationally different ways, depending on which constituent signals are present. Across head movement, an object orientation is remembered and updated relative to the perceived gravity direction as a reference. This shows that tracking objects is based neither on only visual information, nor on only vestibular information about head orientation, but on a visuovestibular estimate of world-vertical. The percept of vertical is crucial in many, if not most, of our interactions with the world. In order to make this percept as accurate as possible, information from multiple sensory systems is combined in a way that is optimal given the nature of the perceptual task at hand, and the nature and reliability of the available sensory signals.