Jörges, B. | Search bioRxiv

bioRxiv2026

Evidence for a Vestibular Contribution to Object Motion Prediction

Humans can predict an objects motion better if its movements are consistent with gravity. Here we investigate whether this may be due to an internalized strong Earth gravity prior or to vestibular cues reporting instantaneous information about gravity. These two directions can be separated using virtual reality by providing strong visual cues to the direction of up which may or may not be aligned with true gravity. Participants were presented with a ball travelling on a parabola path simulated with either downward acceleration created by simulated Earths gravity (1g) or inverted gravity (-1g) resulting in the ball curving upwards. In both types of trial, the ball disappeared at between 57.5% and 75% of its full trajectory - after it had started its descent in the case of 1g or ascent in the case of -1g. Participants pressed a mouse button when they judged the ball to have got back to the height at which it was launched. Participants were either standing or supine. There were no differences in the estimated time to reach the indicated level between the 1g and -1g simulations nor between lying and sitting.A control experiment showed that reaction times were also not significantly different while lying supine versus while upright. Fiinally, to isolate a vestibular component we compared performance during disruptive galvanic vestibular stimulation (dGVS) or during sham stimulation. As when lying supine, the perceived time for the ball to reach the target height was not significantly different between dGVS and sham stimulation. Overall, participants were - surprisingly - no better at anticipating 1g motion compared to -1g motion, and we also dont find a significantly influence of the vestibular system more generally.

neuroscience↗

bioRxiv2023

The Impact of Visually Simulated Self-Motion on Predicting Object Motion

To interact successfully with moving objects in our environment we need to be able to predict their behavior. Predicting the position of a moving object requires an estimate of its velocity. When flow parsing during self-motion is incomplete - that is, when some of the retinal motion created by self-motion is incorrectly attributed to object motion - object velocity estimates become biased. Further, the process of flow parsing should add noise and lead to object velocity judgements being more variable during selfmotion. Biases and lowered precision in velocity estimation should then translate to biases and lowered precision in motion extrapolation. We investigated this relationship between self-motion, velocity estimation and motion extrapolation with two tasks performed in a realistic virtual reality (VR) environment: first, participants were shown a ball moving laterally which disappeared after a certain time. They then indicated by button press when they thought the ball would have hit a target rectangle positioned in the environment. While the ball was visible, participants sometimes experienced simultaneous visual lateral self-motion in either the same or in the opposite direction of the ball. The second task was a two-interval forced choice task in which participants judged which of two motions was faster: in one interval they saw the same ball they observed in the first task while in the other they saw a ball cloud whose speed was controlled by a PEST staircase. While observing the single ball, they were again moved visually either in the same or opposite direction as the ball or they remained static. We found the expected biases in estimated time-to-contact, while for the speed estimation task, this was only the case when the ball and observer were moving in opposite directions. Our hypotheses regarding precision were largely unsupported by the data. Overall, we draw several conclusions from this experiment: first, incomplete flow parsing can affect motion prediction. Further, it suggests that time-to-contact estimation and speed judgements are determined by partially different mechanisms. Finally, and perhaps most strikingly, there appear to be certain compensatory mechanisms at play that allow for much higher-than-expected precision when observers are experiencing self-motion - even when self-motion is simulated only visually.

neuroscience↗