Up, Down, Near, Far: An Online Vestibular Contribution to Distance Judgement

Induced electric fields in MRI settings and electric vestibular stimulations: same vestibular effects?

In Magnetic Resonance Imaging scanner environments, the continuous Lorentz Force is a potent vestibular stimulation. It is nowadays so well known that it is now identified as Magnetic vestibular stimulation (MVS). Alongside MVS, some authors argue that through induced electric fields, electromagnetic induction could also trigger the vestibular system. Indeed, for decades, vestibular-specific electric stimulations (EVS) have been known to precisely impact all vestibular pathways. Here, we go through the literature, looking at potential time varying magnetic field induced vestibular outcomes in MRI settings and comparing them with EVS-known outcomes. To date, although theoretically induction could trigger vestibular responses the behavioral evidence remains poor. Finally, more vestibular-specific work is needed.

A non-image-forming visual circuit mediates the innate fear of heights in male mice

The neural basis of fear of heights remains largely unknown. In this study, we investigated the fear response to heights in male mice and observed characteristic aversive behaviors resembling human height vertigo. We identified visual input as a critical factor in mouse reactions to heights, while peripheral vestibular input was found to be nonessential for fear of heights. Unexpectedly, we found that fear of heights in naïve mice does not rely on image-forming visual processing by the primary visual cortex. Instead, a subset of neurons in the ventral lateral geniculate nucleus (vLGN), which connects to the lateral/ventrolateral periaqueductal gray (l/vlPAG), drives the expression of fear associated with heights. Additionally, we observed that a subcortical visual pathway linking the superior colliculus to the lateral posterior thalamic nucleus inhibits the defensive response to height threats. These findings highlight a rapid fear response to height threats through a subcortical visual and defensive pathway from the vLGN to the l/vlPAG.

Optical and gravito-inertial contributions to the perception and control of height in a simulated Low-Altitude Flight context

Low-Altitude Flight (LAF) is a flight formation consisting of rapid close ground flight. Perception and control of self-motion, allowing for optimal information collection and rapid adaptation, are of fundamental importance during LAF, but remain largely unexplored. This study aimed to analyse the impact of visuo-vestibular stimuli on the monitoring of height in a motion-based simulated LAF context. Thirteen non-pilots were tested in different environmental conditions, in which optical and gravito-inertial (GI) information were manipulated. The visual environment, displayed with a VR headset, was a low-textured landscape with identical and equally spaced trees throughout the trials. The GI environment was designed thanks to a motion-based simulator. Results showed that participants had better performances in a visuo-vestibular environment than in a visual-only setting, indicating that multi-sensory information was picked-up faster than a mono-sensory structure. Additionally, we found differences in the contribution of vestibular inputs depending on the kind of task. Practitioner summary: Low-Altitude-Flight (LAF) manoeuvres require delicate aircraft control. Two experiments using a large flight simulator investigated how visual and vestibular stimulation contribute to LAF perception and control. Results suggest that both sources of stimulation need to be combined for accurate performance, with consequences for simulator-based training scenarios. Abbreviations: LAF: low altitude flight; GI: gravito-inertial; 1/2/3D: 1/2/3 dimensions; VR: virtual reality; Mvt: movement; GVE: good visual environment; DVE: degraded visual environment; SSQ: simulator motion sickness questionnary; RT: reaction time; DIMSS: dynamic interface modelling and simulation system metric; corrAcf: maximum correlation coefficient; corrLag: maximum correlation lag; DFT: deviation from target; StdJ: standard deviation of the joytick value; NCR: number of control reversal.

Horizontal and Vertical Distance Perception in Altered Gravity

The perception of the horizontal and vertical distances of a visual target to an observer was investigated in parabolic flight during alternating short periods of normal gravity (1 g). microgravity (0 g), and hypergravity (1.8 g). The methods used for obtaining absolute judgments of egocentric distance included verbal reports and visually directed motion toward a memorized visual target by pulling on a rope with the arms (blind pulling). The results showed that, for all gravity levels, the verbal reports of distance judgments were accurate for targets located between 0.6 and 6.0 m. During blind pulling, subjects underestimated horizontal distances as distances increased, and this underestimation decreased in 0 g. Vertical distances for up targets were overestimated and vertical distances for down targets were underestimated in both 1 g and 1.8 g. This vertical asymmetry was absent in 0 g. The results of the present study confirm that blind pulling and verbal reports are independently influenced by gravity. The changes in distance judgments during blind pulling in 0 g compared to 1 g support the view that, during an action-based task, subjects base their perception of distance on the estimated motor effort of navigating to the perceived object.

Getting ready for Mars: How the brain perceives new simulated gravitational environments

On Earth, we are continually exposed to gravity: sensory signals are constantly integrated to form an internal model of gravity. However, it is unclear whether this internal model is fixed to Earth's gravity or whether it can be applied to a new gravitational environment. Under terrestrial gravity, observers show a "gravitational bias" while judging the speed of falling versus rising objects, as they comply with the physical laws of gravity. We investigated whether this gravitational bias may be present when judging the speed of objects moving upwards or downwards in both virtual reality (VR)-simulated Earth gravity (9.81 m/s²) and Mars gravity (3.71 m/s²). Our results highlighted a gravitational bias in both Earth and Mars VR-simulated gravity: the speed of downwards movement was more precisely detected than the speed of upwards movement. Although the internal model of gravity has been built up under terrestrial gravity, it can quickly expand to novel non-terrestrial gravitational environments.

The aesthetics of verticality: A gravitational contribution to aesthetic preference

Verticality plays a fundamental role in the arts, portraying concepts such as power, grandeur, or even morality; however, it is unclear whether people have an aesthetic preference for vertical stimuli. The perception of verticality occurs by integrating vestibular-gravitational input with proprioceptive signals about body posture. Thus, these signals may influence the preference for verticality. Here, we show that people have a genuine aesthetic preference for stimuli aligned with the vertical, and this preference depends on the position of the body relative to the gravitational direction. Observers rated the attractiveness of lines that varied in inclination. Perfectly vertical lines were judged to be more attractive than those inclined clockwise or anticlockwise only when participants held an upright posture. Critically, this preference was not present when their body was tilted away from the gravitational vertical. Our results showed that gravitational signals make a contribution to the perception of attractiveness of environmental objects.