Matching optical flow to motor speed in virtual reality while running on a treadmill

Multisensory cues for walking in virtual reality: humans combine conflicting visual and self-motion information to reproduce distances

When humans walk, it is important for them to have some measure of the distance they have traveled. Typically, many cues from different modalities are available, as humans perceive both the environment around them (for example, through vision and haptics) and their own walking. Here, we investigate the contribution of visual cues and nonvisual self-motion cues to distance reproduction when walking on a treadmill through a virtual environment by separately manipulating the speed of a treadmill belt and of the virtual environment. Using mobile eye tracking, we also investigate how our participants sampled the visual information through gaze. We show that, as predicted, both modalities affected how participants (N = 28) reproduced a distance. Participants weighed nonvisual self-motion cues more strongly than visual cues, corresponding also to their respective reliabilities, but with some interindividual variability. Those who looked more toward those parts of the visual scene that contained cues to speed and distance tended also to weigh visual information more strongly, although this correlation was nonsignificant, and participants generally directed their gaze toward visually informative areas of the scene less than expected. As measured by motion capture, participants adjusted their gait patterns to the treadmill speed but not to walked distance. In sum, we show in a naturalistic virtual environment how humans use different sensory modalities when reproducing distances and how the use of these cues differs between participants and depends on information sampling.NEW & NOTEWORTHY Combining virtual reality with treadmill walking, we measured the relative importance of visual cues and nonvisual self-motion cues for distance reproduction. Participants used both cues but put more weight on self-motion; weight on visual cues had a trend to correlate with looking at visually informative areas. Participants overshot distances, especially when self-motion was slow; they adjusted steps to self-motion cues but not to visual cues. Our work thus quantifies the multimodal contributions to distance reproduction.

Walking humans and running mice: perception and neural encoding of optic flow during self-motion

Locomotion produces full-field optic flow that often dominates the visual motion inputs to an observer. The perception of optic flow is in turn important for animals to guide their heading and interact with moving objects. Understanding how locomotion influences optic flow processing and perception is therefore essential to understand how animals successfully interact with their environment. Here, we review research investigating how perception and neural encoding of optic flow are altered during self-motion, focusing on locomotion. Self-motion has been found to influence estimation and sensitivity for optic flow speed and direction. Nonvisual self-motion signals also increase compensation for self-driven optic flow when parsing the visual motion of moving objects. The integration of visual and nonvisual self-motion signals largely follows principles of Bayesian inference and can improve the precision and accuracy of self-motion perception. The calibration of visual and nonvisual self-motion signals is dynamic, reflecting the changing visuomotor contingencies across different environmental contexts. Throughout this review, we consider experimental research using humans, non-human primates and mice. We highlight experimental challenges and opportunities afforded by each of these species and draw parallels between experimental findings. These findings reveal a profound influence of locomotion on optic flow processing and perception across species. This article is part of a discussion meeting issue 'New approaches to 3D vision'.

The study of virtual reality influence on the process of professional training of miners

Virtual reality technologies are actively applied for the organization of professional training in various industries, as well as in distance learning. However, numerous studies show the presence of a large number of negative factors that limit the effectiveness of using these technologies (united by the concept of "cybersickness"). The study, identification and reduction in the influence of these negative factors will increase the immersiveness and quality of the professional training process. Within the framework of this study, several hypotheses have been put forward regarding the negative and positive impact of VR technologies on the process of professional training, the coal and mining industry has been chosen as the subject area. Thus, the problem of effective training of miners for activities in regular and emergency situations is considered, in the latter case, VR technologies would allow forming the necessary set of skills and knowledge about actions in emergency situations. To confirm the declared hypotheses, an experimental group of 30 people was formed, corresponding to the trained miners by age characteristics. Based on the analysis, a list of quantitative and qualitative metrics for evaluating interaction with virtual reality was formed, the software of virtual scenes for two tasks (moving simple objects and a set of exercises in a virtual mine) was developed. The experimental group repeatedly performed these exercises, which allowed us to analyze the dynamics of changes in the average values of quantitative and qualitative metrics. The data obtained were processed by statistical tests (Shapiro-Wilk, Kruskal-Wallis, Mann-Whitney), which allowed us to assess the impact of the selected configurations (with and without VR) and the number of attempts on the selected metrics. The obtained results partially or completely confirmed the declared hypotheses and allowed us to form a list of recommendations for the organization of high-quality professional training using virtual reality technologies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10055-022-00687-7.

Perceptual Awareness of Optic Flows Paced Optimally and Non-optimally to Walking Speed

Previous research suggests that visual processing depends strongly on locomotor activity and is tuned to optic flows consistent with self-motion speed. Here, we used a binocular rivalry paradigm to investigate whether perceptual access to optic flows depends on their optimality in relation to walking velocity. Participants walked at two different speeds on a treadmill while viewing discrepant visualizations of a virtual tunnel in each eye. We hypothesized that visualizations paced appropriately to the walking speeds will be perceived longer than non optimal (too fast/slow) ones. The presented optic flow speeds were predetermined individually in a task based on matching visual speed to both walking velocities. In addition, perceptual preference for optimal optic flows was expected to increase with proprioceptive ability to detect threshold-level changes in walking speed. Whereas faster (more familiar) optic flows showed enhanced access to awareness during faster compared with slower walking conditions, for slower visual flows, only a nonsignificant tendency for the analogous effect was observed. These effects were not dependent on individual proprioceptive sensitivity. Our findings concur with the emerging view that the velocity of one's locomotion is used to calibrate visual perception of self-motion and extend the scope of reported action effects on visual awareness.

Treadmill and Running Speed Effects on Acceleration Impacts: Curved Non-Motorized Treadmill vs. Conventional Motorized Treadmill

An increase in the popularity of running can be seen over the last decades, with a large number of injuries on it. Most of the running injuries are related to impact accelerations and are due to overuse. In order to reduce the risk of injury or to improve performance and health new treadmill designs have been created, as it can be the curved non-motorized treadmill. The aim of this study was to analyse impact accelerations, spatio-temporal parameters and perceptual differences while running on curved non-motorized treadmill (cNMT) compared to motorized treadmill (MT) at different speeds. Therefore, 27 recreational runners completed two tests consisting of 10 min warm-up and three bouts of 8 min running at 2.77 m/s, 3.33 m/s and self-selected speed on cNMT and MT, previously randomised. Although the surface did not influence spatio-temporal parameters, a reduction in impact accelerations, head acceleration rate (mean effect size [ES] = 0.86), tibia peak (mean ES = 0.45) and tibia magnitude (mean ES = 0.55), was observed while running on cNMT in comparison with running on MT. Moreover, higher heart rate (HR) (mean ES = 0.51) and rating of perceived effort (RPE) (mean ES = 0.34) were found while running on cNMT. These findings demonstrated that higher intensity training and lower impact accelerations are experimented on cNMT, what can be used by trainers and athletes while planning training sessions.

Forward optic flow is prioritised in visual awareness independently of walking direction

When two different images are presented separately to each eye, one experiences smooth transitions between them-a phenomenon called binocular rivalry. Previous studies have shown that exposure to signals from other senses can enhance the access of stimulation-congruent images to conscious perception. However, despite our ability to infer perceptual consequences from bodily movements, evidence that action can have an analogous influence on visual awareness is scarce and mainly limited to hand movements. Here, we investigated whether one's direction of locomotion affects perceptual access to optic flow patterns during binocular rivalry. Participants walked forwards and backwards on a treadmill while viewing highly-realistic visualisations of self-motion in a virtual environment. We hypothesised that visualisations congruent with walking direction would predominate in visual awareness over incongruent ones, and that this effect would increase with the precision of one's active proprioception. These predictions were not confirmed: optic flow consistent with forward locomotion was prioritised in visual awareness independently of walking direction and proprioceptive abilities. Our findings suggest the limited role of kinaesthetic-proprioceptive information in disambiguating visually perceived direction of self-motion and indicate that vision might be tuned to the (expanding) optic flow patterns prevalent in everyday life.

Is Motorized Treadmill Running Biomechanically Comparable to Overground Running? A Systematic Review and Meta-Analysis of Cross-Over Studies

BACKGROUND

Treadmills are often used in research, clinical practice, and training. Biomechanical investigations comparing treadmill and overground running report inconsistent findings.

OBJECTIVE

This study aimed at comparing biomechanical outcomes between motorized treadmill and overground running.

METHODS

Four databases were searched until June 2019. Crossover design studies comparing lower limb biomechanics during non-inclined, non-cushioned, quasi-constant-velocity motorized treadmill running with overground running in healthy humans (18-65 years) and written in English were included. Meta-analyses and meta-regressions were performed where possible.

RESULTS

33 studies (n = 494 participants) were included. Most outcomes did not differ between running conditions. However, during treadmill running, sagittal foot-ground angle at footstrike (mean difference (MD) - 9.8° [95% confidence interval: - 13.1 to - 6.6]; low GRADE evidence), knee flexion range of motion from footstrike to peak during stance (MD 6.3° [4.5 to 8.2]; low), vertical displacement center of mass/pelvis (MD - 1.5 cm [- 2.7 to - 0.8]; low), and peak propulsive force (MD - 0.04 body weights [- 0.06 to - 0.02]; very low) were lower, while contact time (MD 5.0 ms [0.5 to 9.5]; low), knee flexion at footstrike (MD - 2.3° [- 3.6 to - 1.1]; low), and ankle sagittal plane internal joint moment (MD - 0.4 Nm/kg [- 0.7 to - 0.2]; low) were longer/higher, when pooled across overground surfaces. Conflicting findings were reported for amplitude of muscle activity.

CONCLUSIONS

Spatiotemporal, kinematic, kinetic, muscle activity, and muscle-tendon outcome measures are largely comparable between motorized treadmill and overground running. Considerations should, however, particularly be given to sagittal plane kinematic differences at footstrike when extrapolating treadmill running biomechanics to overground running. Protocol registration CRD42018083906 (PROSPERO International Prospective Register of Systematic Reviews).

Setting, Age, and Intensity Influence Responses to Exercise in Young Endurance Runners

We investigated the effects of exercise setting (indoor treadmill vs. outdoor trail), age (17 middle school, 18 high school, and 13 college participants), and level of exertion (Borg Ratings of Perceived Exertion of 10, 12, and 16 on a 22-point scale) on young male endurance runners’ heart rate (HR), running speed, attentive focus, and affect. Three-way analyses of variance revealed that on the outdoor trail (vs. indoor treadmill), HR and speed were higher ( p < .001) and attentive focus was more dissociative ( p = .047). There were significant Age × Setting interactions for HR ( p = .047), speed ( p = .023), and attentive focus ( p = .002), with older participants exhibiting a greater increase in speed and HR and a greater shift toward dissociative focus on the outdoor trail. Three-way analyses of variance also yielded significant Age × Time interactions on components of the Physical Activity Affect Scale in that younger participants exhibited larger declines in positive affect ( p = .003) and tranquility ( p < .001) and larger increases in fatigue ( p < .001) as a result of the running session. Our data suggest that either runners develop more positive responses to exercise as they mature or those young runners who experience running more negatively tend to drop out of running so that the remaining older participants continuing to run are those who experience exercise positively.

A Biologically-Inspired Model to Predict Perceived Visual Speed as a Function of the Stimulated Portion of the Visual Field

Spatial orientation relies on a representation of the position and orientation of the body relative to the surrounding environment. When navigating in the environment, this representation must be constantly updated taking into account the direction, speed, and amplitude of body motion. Visual information plays an important role in this updating process, notably via optical flow. Here, we systematically investigated how the size and the simulated portion of the field of view (FoV) affect perceived visual speed of human observers. We propose a computational model to account for the patterns of human data. This model is composed of hierarchical cells' layers that model the neural processing stages of the dorsal visual pathway. Specifically, we consider that the activity of the MT area is processed by populations of modeled MST cells that are sensitive to the differential components of the optical flow, thus producing selectivity for specific patterns of optical flow. Our results indicate that the proposed computational model is able to describe the experimental evidence and it could be used to predict expected biases of speed perception for conditions in which only some portions of the visual field are visible.

No Evidence That Frontal Optical Flow Affects Perceived Locomotor Speed and Locomotor Biomechanics When Running on a Treadmill

We investigated how the presentation and the manipulation of an optical flow while running on a treadmill affect perceived locomotor speed (Experiment 1) and gait parameters (Experiment 2). In Experiment 1, 12 healthy participants were instructed to run at an imposed speed and to focus on their sensorimotor sensations to be able to reproduce this running speed later. After a pause, they had to retrieve the reference locomotor speed by manipulating the treadmill speed while being presented with different optical flow conditions, namely no optical flow or a matching/slower/faster optical flow. In Experiment 2, 20 healthy participants ran at a previously self-selected constant speed while being presented with different optical flow conditions (see Experiment 1). The results did not show any effect of the presence and manipulation of the optical flow either on perceived locomotor speed or on the biomechanics of treadmill running. Specifically, the ability to retrieve the reference locomotor speed was similar for all optical flow conditions. Manipulating the speed of the optical flow did not affect the spatiotemporal gait parameters and also failed to affect the treadmill running accommodation process. Nevertheless, the virtual reality conditions affected the heart rate of the participants but without affecting perceived effort.

Influence of the Size of the Field of View on Visual Perception While Running in a Treadmill-Mediated Virtual Environment

We investigated how the size of the horizontal field of view (FoV) affects visual speed perception with individuals running on a treadmill. Twelve moderately trained to trained participants ran on a treadmill at two different speeds (8 and 12 km/h) in front of a moving virtual scene. Different masks were used to manipulate the visible visual field, masking either the central or the peripheral area of the virtual scene or showing the full visual field. We asked participants to match the visual speed of the scene to their actual running speed. For each trial, participants indicated whether the scene was moving faster or slower than they were running. Visual speed was adjusted according to the responses using a staircase method until the Point of Subjective Equality was reached, that is until visual and running speed were perceived as matching. For both speeds and all FoV conditions, participants underestimated visual speed relative to the actual running speed. However, this underestimation was significant only when the peripheral FoV was masked. These results confirm that the size of the FoV should absolutely be taken into account for the design of treadmill-mediated virtual environments (VEs).

Regular physical activity modulates perceived visual speed when running in treadmill-mediated virtual environments

In virtual reality, visual speed is usually underestimated relative to locomotor speed. Here we investigated how physical activity and fitness affect perceived visual speed when running in a treadmill-mediated virtual environment. Thirty healthy participants (ten sedentary individuals, ten team sport players and ten expert runners) ran on a treadmill at two different speeds (8, 12km/h) in front of a moving virtual scene. Participants were asked to match the speed of the visual scene to their running speed (i.e. treadmill speed), indicating for each trial whether the scene was moving slower or faster than the treadmill. The speed of the visual scene was adjusted according to the participant’s response using a staircase until visual and running speeds were perceived as equivalent. More sedentary participants underestimated visual speed relative to their actual running speed. Specifically, visual speed had to exceed running speed to be perceived as equivalent. The underestimation of visual speed was speed-dependent, and it was significantly larger for sedentary participants than for team sports players and expert runners. The volume of physical activity per week was found to be the best predictor of visual speed perception for both running speeds, while the perceived effort constituted a good predictor only at 8km/h. Physical fitness, on the other hand turned out to be a poor predictor of visual speed perception. Therefore, in order to enhance users’ engagement and their adherence to physical activity programs, the development of “personalized” treadmill-mediated virtual environments should take into account users’ personal characteristics to provide the most natural and engaging feedback possible.