Monocular vision and increased distance reducing the effects of visual manipulation on body sway

Eye Position Shifts Body Sway Under Foot Dominance Bias in the Absence of Visual Feedback

Purpose

The purpose of this study was to investigate whether information on extraocular muscle proprioception without visual information affects postural control.

Methods

Thirty-five healthy young volunteers participated in the study. Postural control outcomes included the center of pressure (CoP) for static standing, the total length of the sway of the CoP (LNG), and the sway area (SA), as well as the mean CoP in the mediolateral and anteroposterior directions. The following five eye-fixing positions were used: eye-up (E-Up), eye-down (E-Down), eye-right (E-Right), eye-left (E-Left), and eye-center (Center eye position). One-way ANOVA and Bonferroni correction was performed for statistical processing. Electrooculograms were recorded to detect eye orientation errors, measured with the eyes closed.

Results

The results of this study showed no significant difference between the LNG and SA results when comparing respective eye positions (E-up, E-down, E-right, E-left) relative to E-Center (control). However, the average CoP was shifted to the right at E-Up, E-Down, and E-Left.

Conclusion

These findings indicate that postural control may be affected by eye-body coordination depending on the position of the eyes, even without visual information.

Vision-based speedometer regulates human walking

Can we recover self-motion from vision? This basic issue remains unsolved since, while the human visual system is known to estimate the direction of self-motion from optic flow, it remains unclear whether it also estimates the speed. Importantly, the latter requires disentangling self-motion speed and depths of objects in the scene as retinal velocity depends on both. Here we show that our automatic regulator of walking speed based on vision, which estimates and maintains the speed to its preferred range by adjusting stride length, is robust to changes in the depths. The robustness was not explained by temporal-frequency-based speed coding previously suggested to underlie depth-invariant object-motion perception. Meanwhile, it broke down, not only when the interocular distance was virtually manipulated but also when monocular depth cues were deceptive. These observations suggest that our visuomotor system embeds a speedometer that calculates self-motion speed from vision by integrating monocular/binocular depth and motion cues.

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Changes in optic flow speed triggers implicit adjustments of walking speed

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The response is invariant with respect to the depths of objects in the scene

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The invariance is not explained by temporal-frequency-based speed coding

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Both binocular and monocular depth cues contribute to the invariance

Application of Real-Time Visual Feedback System in Balance Training of the Center of Pressure with Smart Wearable Devices

Balance control with an upright posture is affected by many factors. This study was undertaken to investigate the effects of real-time visual feedback training, provided by smart wearable devices for COP changes for healthy females, on static stance. Thirty healthy female college students were randomly divided into three groups (visual feedback balance training group, non-visual feedback balance training group, and control group). Enhanced visual feedback on the screen appeared in different directions, in the form of fluctuations; the visual feedback balance training group received real-time visual feedback from the Podoon APP for training, while the non-visual feedback balance training group only performed an open-eye balance, without receiving real-time visual feedback. The control group did not do any balance training. The balance training lasted 4 weeks, three times a week for 30 min each time with 1-2 day intervals. After four weeks of balance training, the results showed that the stability of human posture control improved for the one leg static stance for the visual feedback balance training group with smart wearable devices. The parameters of COP max displacement, COP velocity, COP radius, and COP area in the visual feedback balance training group were significantly decreased in the one leg stance (p < 0.05). The results showed that the COP real-time visual feedback training provided by smart wearable devices can better reduce postural sway and improve body balance ability than general training, when standing quietly.

Larger Head Displacement to Optic Flow Presented in the Lower Visual Field

Optic flow that simulates self-motion often produces postural adjustment. Although literature has suggested that human postural control depends largely on visual inputs from the lower field in the environment, effects of the vertical location of optic flow on postural responses are not well investigated. Here, we examined whether optic flow presented in the lower visual field produces stronger responses than optic flow in the upper visual field. Either expanding or contracting optic flow was presented in upper, lower, or full visual fields through an Oculus Rift head-mounted display. Head displacement and vection strength were measured. Results showed larger head displacement under the optic flow presentation in the full visual field and the lower visual field than the upper visual field, during early period of presentation of the contracting optic flow. Vection was strongest in the full visual field and weakest in the upper visual field. Our findings of lower field superiority in head displacement and vection support the notion that ecologically relevant information has a particularly important role in human postural control and self-motion perception.

Effects of Age-Related Macular Degeneration on Postural Sway

Purpose: To compare the impact of unilateral vs. bilateral age-related macular degeneration (AMD) on postural sway, and the influence of different visual conditions. The hypothesis of our study was that the impact of AMD will be different between unilateral and bilateral AMD subjects compared to age-matched healthy elderly.

Methods: Postural stability was measured with a platform (TechnoConcept®) in 10 elderly unilateral AMD subjects (mean age: 71.1 ± 4.6 years), 10 elderly bilateral AMD subjects (mean age: 70.8 ± 6.1 years), and 10 healthy age-matched control subjects (mean age: 69.8 ± 6.3 years). Four visual conditions were tested: both eyes viewing condition (BEV), dominant eye viewing (DEV), non-dominant eye viewing (NDEV), and eyes closed (EC). We analyzed the surface area, the length, the mean speed, the anteroposterior (AP), and mediolateral (ML) displacement of the center of pressure (CoP).

Results: Bilateral AMD subjects had a surface area (p < 0.05) and AP displacement of the CoP (p < 0.01) higher than healthy elderly. Unilateral AMD subjects had more AP displacement of the CoP (p < 0.05) than healthy elderly.

Conclusions: We suggest that ADM subjects could have poor postural adaptive mechanisms leading to increase their postural instability. Further studies will aim to improve knowledge on such issue and to develop reeducation techniques in these patients.

Quality of Visual Cue Affects Visual Reweighting in Quiet Standing

Sensory reweighting is a characteristic of postural control functioning adopted to accommodate environmental changes. The use of mono or binocular cues induces visual reduction/increment of moving room influences on postural sway, suggesting a visual reweighting due to the quality of available sensory cues. Because in our previous study visual conditions were set before each trial, participants could adjust the weight of the different sensory systems in an anticipatory manner based upon the reduction in quality of the visual information. Nevertheless, in daily situations this adjustment is a dynamical process and occurs during ongoing movement. The purpose of this study was to examine the effect of visual transitions in the coupling between visual information and body sway in two different distances from the front wall of a moving room. Eleven young adults stood upright inside of a moving room in two distances (75 and 150 cm) wearing a liquid crystal lenses goggles, which allow individual lenses transition from opaque to transparent and vice-versa. Participants stood still during five minutes for each trial and the lenses status changed every one minute (no vision to binocular vision, no vision to monocular vision, binocular vision to monocular vision, and vice-versa). Results showed that farther distance and monocular vision reduced the effect of visual manipulation on postural sway. The effect of visual transition was condition dependent, with a stronger effect when transitions involved binocular vision than monocular vision. Based upon these results, we conclude that the increased distance from the front wall of the room reduced the effect of visual manipulation on postural sway and that sensory reweighting is stimulus quality dependent, with binocular vision producing a much stronger down/up-weighting than monocular vision.

Dyslexic children suffer from less informative visual cues to control posture

The goal of this study was to investigate the effects of manipulation of the characteristics of visual stimulus on postural control in dyslexic children. A total of 18 dyslexic and 18 non-dyslexic children stood upright inside a moving room, as still as possible, and looked at a target at different conditions of distance between the participant and a moving room frontal wall (25-150 cm) and vision (full and central). The first trial was performed without vision (baseline). Then four trials were performed in which the room remained stationary and eight trials with the room moving, lasting 60s each. Mean sway amplitude, coherence, relative phase, and angular deviation were calculated. The results revealed that dyslexic children swayed with larger magnitude in both stationary and moving conditions. When the room remained stationary, all children showed larger body sway magnitude at 150 cm distance. Dyslexic children showed larger body sway magnitude in central compared to full vision condition. In the moving condition, body sway magnitude was similar between dyslexic and non-dyslexic children but the coupling between visual information and body sway was weaker in dyslexic children. Moreover, in the absence of peripheral visual cues, induced body sway in dyslexic children was temporally delayed regarding visual stimulus. Taken together, these results indicate that poor postural control performance in dyslexic children is related to how sensory information is acquired from the environment and used to produce postural responses. In conditions in which sensory cues are less informative, dyslexic children take longer to process sensory stimuli in order to obtain precise information, which leads to performance deterioration.

Influence of gaze distance and downward gazing on postural sway in hemiplegic stroke patients

Gaze distance and head flexion suppress postural sway in healthy subjects. However, the effects of these factors on stroke patients have not been fully elucidated. In this study, we aimed to evaluate the effects of gaze distance and downward gazing on postural sway in stroke patients. We examined 15 stroke patients and 14 elderly controls. Postural sway was measured in the subjects under the following 5 conditions: eyes fixed forward on a marker located 600 cm ahead (600-cm condition); eyes fixed forward on a marker located 150 cm ahead (150-cm condition); eyes fixed downward (downward condition); the subject facing straight ahead but with eyes closed (closed-forward condition); and the subject facing downward but with eyes closed (closed-downward condition). The root mean squares of the anteroposterior (A-P RMS) and the mediolateral (M-L RMS) directions were determined. The results showed that the short gaze distance decreased the M-L RMS in both the stroke patients and controls (p < 0.001, r = 0.66; p = 0.024, r = 0.43, respectively). In the control group, the downward condition increased the M-L RMS when compared with the 600-cm condition (p = 0.011, r = 0.48). The downward condition decreased the A-P and M-L RMS in the stroke patients when compared with the 600-cm condition (A-P RMS: p < 0.001; r = 0.66, M-L RMS: p = 0.001; r = 0.59). Our results showed that the short gaze distance decreased postural sway in both groups, and downward gazing decreased it only in the stroke group.