The influence of moving auditory stimuli on standing balance in healthy young adults and the elderly

The maintenance of postural balance depends on effective and efficient feedback from various sensory inputs. The importance of auditory inputs in this respect is not, as yet, fully understood. The purpose of this study was to analyse how the moving auditory stimuli could affect the standing balance in healthy adults of different ages. The participants of the study were 12 healthy volunteers, who were divided into two age categories: the young group (mean = 21.9 years) and the elderly group (mean = 68.9 years). The instrument used for evaluation of standing balance was a force plate for measuring body sway parameters. The toe pressure was measured using the F-scan Tactile Sensor System. The moving auditory stimulus produced a white-noise sound and binaural cue using the Beachtron Affordable 3D Audio system. The moving auditory stimulus conditions were employed by having the sound come from the right to left or vice versa at the height of the participant's ears. Participants were asked to stand on the force plate in the Romberg position for 20 s with either eyes opened or eyes closed for analysing the effect of visual input. Simultaneously, all participants tried to remain in the standing position with and without auditory stimulation that the participants heard from the headphone. In addition, the variables of body sway were measured under four conditions for analysing the effect of decreased tactile sensation of toes and feet soles: standing on the normal surface (NS) or soft surface (SS) with and without auditory stimulation. The participants were asked to stand in a total of eight conditions. The results showed that the lateral body sway of the elderly group was more influenced than that of the young group by the lateral moving auditory stimulation. The analysis of toe pressure indicated that all participants used their left feet more than their right feet to maintain balance. Moreover, the elderly had the tendency to be stabilized mainly by use of their heels. The young group were mainly stabilized by the toes of their feet. The results suggest that the elderly may need a more appropriate stimulus of tactile and auditory sense as a feedback system than the young for maintaining and control of their standing postures.     

Postural stability effects of random vibration at the feet of construction workers in simulated elevation

The risk of falls from height on a construction site increases under conditions which degrade workers’ postural control. At elevation, workers depend heavily on sensory information from their feet to maintain balance. The study tested two hypotheses: “sensory enhancement” – sub-sensory (undetectable) random mechanical vibrations at the plantar surface of the feet can improve worker’s balance at elevation; and “sensory suppression” – supra-sensory (detectable) random mechanical vibrations can have a degrading effect on balance in the same experimental settings.Six young (age 20–35) and six aging (age 45–60) construction workers were tested while standing in standard and semi-tandem postures on instrumented gel insoles. The insoles applied sub- or supra-sensory levels of random mechanical vibrations to the feet. The tests were conducted in a surround-screen virtual reality system, which simulated a narrow plank at elevation on a construction site. Upper body kinematics was assessed with a motion-measurement system. Postural stability effects were evaluated by conventional and statistical mechanics sway measures, as well as trunk angular displacement parameters.Analysis of variance did not confirm the “sensory enhancement” hypothesis, but provided evidence for the “sensory suppression” hypothesis. The supra-sensory vibration had a destabilizing effect, which was considerably stronger in the semi-tandem posture and affected most of the sway variables.Sensory suppression associated with elevated vibration levels on a construction site may increase the danger of losing balance. Construction workers at elevation, e.g., on a beam or narrow plank might be at increased risk of fall if they can detect vibrations under their feet. To reduce the possibility of losing balance, mechanical vibration to supporting structures used as walking/working surfaces should be minimized when performing construction tasks at elevation.     

The effects of a lower body exoskeleton load carriage assistive device on limits of stability and postural sway

The study investigated the effects of using a lower body prototype exoskeleton (EXO) on static limits of stability and postural sway. Measurements were taken with participants, 10 US Army enlisted men, standing on a force platform. The men were tested with and without the EXO (15 kg) while carrying military loads of 20, 40 and 55 kg. Body lean to the left and right was significantly less and postural sway excursions and maximal range of movement were significantly reduced when the EXO was used. Hurst values indicated that body sway was less random over short-term time intervals and more random over long-term intervals with the EXO than without it. Feedback to the user's balance control mechanisms most likely was changed with the EXO. The reduced sway and relatively small changes in sway with increasing load weights suggest that the EXO structure may have functioned to provide a bracing effect on the body.     

The effects of a lower body exoskeleton load carriage assistive device on limits of stability and postural sway

The study investigated the effects of using a lower body prototype exoskeleton (EXO) on static limits of stability and postural sway. Measurements were taken with participants, 10 US Army enlisted men, standing on a force platform. The men were tested with and without the EXO (15 kg) while carrying military loads of 20, 40 and 55 kg. Body lean to the left and right was significantly less and postural sway excursions and maximal range of movement were significantly reduced when the EXO was used. Hurst values indicated that body sway was less random over short-term time intervals and more random over long-term intervals with the EXO than without it. Feedback to the user's balance control mechanisms most likely was changed with the EXO. The reduced sway and relatively small changes in sway with increasing load weights suggest that the EXO structure may have functioned to provide a bracing effect on the body.     

Is active sitting as active as we think?

The aim of this study was to compare the biomechanical characteristics of sitting on a stool without a backrest (so as to encourage active sitting), sitting on a conventional office chair and standing in healthy participants. Thirteen healthy participants performed a keyboard-writing task during four (stable and unstable) sitting conditions and standing. Body segment positions and posture, postural sway and muscle activity of neck and trunk muscles were assessed with a motion capture system, a force plate and surface electromyography. The results showed that body segment positions, postural sway and trunk muscle activity were relatively similar for the stools without backrests compared with standing. All sitting conditions showed lower vertical upper body alignment, less anterior pelvic tilt and larger hip angles, compared with standing (p = 0.000). Unexpectedly, the muscle activity levels and total postural sway, sway velocity and sway in M/L and A/P directions were lower (p = 0.000) for the conditions that encouraged active sitting and standing, compared with the conventional office chair conditions.

Practitioner Summary: Thirteen healthy participants performed a keyboard-writing task during different sitting conditions and standing and were analysed regarding posture, postural sway and trunk muscle activity. Surprisingly, less postural sway and less muscle activity were observed during the conditions that encourage active sitting, compared with sitting on a conventional office chair.     

Evaluation of circumferential pressure as an intervention to mitigate postural instability induced by localized muscle fatigue at the ankle

Pressure application via taping reportedly improves proprioception, and localized muscle fatigue (LMF) increases postural sway, which may be due to a loss of position sense acuity (PSA). This exploratory study investigated the effects of circumferential pressure (CP) and induced ankle LMF on sway. Fourteen young participants performed fatiguing sub-maximal isotonic plantarflexion exercises. Ankle PSA was determined, and used to categorize participants (i.e. high and low groups). Postural sway during quiet standing was assessed using a force platform, both pre- and post-LMF. CP was applied unilaterally to the dominant leg above the ankle joint. Both CP and LMF resulted in greater sway in the low PSA group. CP did not mitigate LMF effects on sway in the low PSA group, but reduced sway among the high PSA group. Reduced PSA may thus indicate less reliance on somatosensation for balance maintenance.

Relevance to industry

Potential benefits of circumferential pressure were indicated. Specifically, CP at the ankle led to improved postural control in certain individuals, which suggests that pressure application might thereby improve balance maintenance and help reduce occupational fall incidents. Results might help to design occupational interventions (specifically CP or taping) differently for individuals with low vs. high PSA.     

Biomechanical response of the human foot when standing in a natural position while exposed to vertical vibration from 10–200 Hz

Exposure to foot-transmitted vibration (FTV) can lead to pain and numbness in the toes and feet, increased cold sensitivity, blanching in the toes, and joint pain. Prolonged exposure can result in a clinical diagnosis of vibration-induced white foot (VIWFt). Data on the biomechanical response of the feet to FTV is limited; therefore, this study seeks to identify resonant frequencies for different anatomical locations on the human foot, while standing in a natural position. A laser Doppler vibrometer was used to measure vertical (z-axis) vibration on 21 participants at 24 anatomical locations on the right foot during exposure to a sine sweep from 10–200?Hz with a peak vertical velocity of 30?mm/s. The most notable differences in the average peak frequency occur between the toes (range: 99–147?Hz), midfoot (range: 51–84?Hz) and ankle (range: 16–39?Hz).

Practitioner Summary: The biomechanical response of the human foot exposed to foot-transmitted vibration, when standing in a natural position, was measured for 21 participants. The foot does not respond uniformly; the toes, midfoot, and ankle regions need to be considered independently in future development of isolation strategies and protective measures.     

Dynamic Studies On Human Body Sway By Using A Simple Model With Special Concerns On The Pelvic And Muscle Roles

The human pelvis is such a unique structure that enables our upper body to work so perfectly with the two legs so as to control the body's balance in the complicated postures. The aim of this study is to establish a new dynamic body sway control model in the upright standing body position in coronal plane, and to reveal the possible control mechanisms underlying the body sway with special concerns on the roles that the pelvis and its muscles are performing during the sway. The plant of control model, the dynamics of human body, includes five parts, i.e. two ankles, two hips and one lumbosacral joint, which makes up a multi‐link inverted pendulum system, and is driven by two pairs of muscles, the psoas major (PM) and glutaeus medius (GM). Body sway records from eight healthy young subjects showed that the angular sway scopes of the ankle on roll (lateral) plane are 0.94±0.36± (eye‐open) and 1.35±0.52± (eye‐closed) respectively, while in lumbosacral plane, the scopes are 0.99±0.41± (eye‐open) and 1.27±0.72± (eye‐closed). The ankle and lumbosacral sways were almost in the same degree, yet their phase difference was near ±n, which means that the body trunk maintains perpendicular to horizon during the upright stance. Surface electromyographic (sEMG) activity from GM also showed the same evidence: the activated GM was always in the same side as the deviated center‐of‐pressure (COP). By assuming the corrective torque of posture is regulated by PID (proportional, integral and derivative) control, the body sway can be simulated by applying human physical parameters. Our study results demonstrated that the simulated traces are consistent with the experimental recorded, suggesting that the pelvis is an important structure for the posture maintenance and control, and the mechanism of balance keeping control during upright stance can be approximately taken as a PID control. The result also suggests a novel means for postural stability assessment in individual in the future.     

Infrared thermography in the hands and feet of hand-arm vibration syndrome (HAVS) cases and controls

This study evaluated IR thermography during 15 min of re-warming after cold water immersion in accordance with ISO guidelines (12 °C for 5 min) in cases with the vascular component of HAVS and controls. The purposes of the study were: (1) To evaluate the performance of IR thermography as a diagnostic test for the vascular effects of HAVS in the fingers, (2) To determine if there were any temperature differences in the toes between cases and controls and, if so, to evaluate the IR thermography as a diagnostic test for toe vascular effects in HAVS. A total of 39 HAVS cases and 46 controls were included in the study. In the fingers, an ROC analysis indicated that the highest areas under the curve (AUC) were obtained at 7 min of re-warming for the fingertips, middle phalanges and proximal phalanges. However, at these locations and time period of re-warming the sensitivities and specificities were not sufficiently high. For example a sensitivity of 66.7% was associated with specificities of 60.9%–67.4%. In the toe analysis 33 (84.6%) cases but only 3 controls (6.5%) reported increased cold intolerance in the feet and this difference was statistically significant (p < 0.001). These 33 cases were then compared to the 46 controls. In the ROC analysis for the toes, the AUC's were lower than those for the fingers and the estimated sensitivities and specificities were worse for the toes than for the fingers. However some statistically significant colder temperatures were found in cases in comparison to controls towards the end of the re-warming period. IR thermography after the ISO recommended cold water stimulation conditions did not perform well as a diagnostic test in the hands or feet. The statistically significant colder temperatures in the toes towards the end of re-warming are relevant to our understanding of foot vascular effects associated with vibration. In industry there is recent interest in determining the effects of foot transmitted vibration (FTV). Many workers have mixed HAV and FTV and it is important to account for feet effects secondary to HAVS in the hands when evaluating the effects of FTV.     

Affective Communication through Air Jet Stimulation: Evidence from Event-Related Potentials

In this article, effectiveness of air jet stimulation in mediated emotional communication was investigated by assessing cross-modal influences of visual emotional expressions on tactile perception. Brain responses to combined visual faces and air jet stimuli were measured using event-related potentials; whereas, emotional responses were assessed using self-reported pleasantness of the tactile stimulation. ERP results reveal significant differences between the different facial expressions for the same tactile air-jet intensity in the somatosensory area. Moreover, participants’ pleasantness ratings suggest an effect of the visual stimulus on the difference tactile conditions that correspond to air jet stimulation intensities: low, medium, and high. These promising results provide evidence in the potential efficiency of this stimulation technique in activating skin receptors that play an important role in social and affective behaviors.     

视听触同步刺激的数字化盲文学习方法

盲文是视障人士获取信息,学习知识的重要媒介.然而,目前基于纸质书籍的盲文学习方法只能提供盲文点位的触觉刺激,存在不便携、不易用且内容陈旧等问题.为此,本文提出了一种视觉、听觉和触觉同步刺激的数字化盲文学习方法,能够提高视障人士的盲文学习效率.基于多感知盲文学习机,本文设计了一种多感知信息匹配算法,能够输出文字、声音和盲文点位相同内容的信息,为视障人士无障碍学习盲文提供条件.短期记忆的盲文学习效果实验表明:(1)在视觉、听觉和触觉的共同刺激下,盲文学习效率最高,即在盲文学习过程中,增加视觉刺激对于视力残余人士提升盲文学习效率有显著正向促进作用;(2)在听觉和触觉的共同刺激下,盲文学习效率并不高,即全盲人士学会盲文有一定难度,需要有较长的学习曲线;(3)仅在听觉刺激下,盲文学习效率很低,即开发语音学盲文的APP不具备实践意义.     

Evaluation of automobile navigation systems with multisensory information channels

Although automobile navigation systems have conventionally utilised visual and auditory modalities to deliver information, recent advancement in tactile technology has introduced the possibility of integrating tactile actuators into navigation systems. To empirically test the effect of tactile navigational cues, we conducted simulated driving experiments in which participants (N?=?96) were exposed to four sets of information modalities (visual, visual?+?auditory, visual?+?tactile, and visual?+?auditory?+?tactile). The results indicate that multisensory systems including tactile cues allow participants to respond faster to unexpected road events and impart greater satisfaction with the overall driving experience. The implications and limitations of these findings are discussed.     

Review of: “Handbook of Psychophysiology. Edited by Norman S. Greenfield and Richard A. Sternbach.” (New York: Holt,Rinehart and Winston, 1972.) [Pp. xii-f-1011.] £14-30.

The purpose of this study was to assess the effects of hip belt use and load placement in a backpack on perceived exertion and postural stability. Thirty participants were instructed to stand on a force plate and walk along a designated route under five conditions: unloaded, high-load placement, low-load placement, hip belt on and hip belt off. The average velocity and sway area from the force plate were measured. Participants also rated their perceived stability and exertion. Compared to the unloaded condition, all loaded conditions significantly increased average velocity, sway area, perceived stability and exertion. Hip belt use did not affect average velocity and sway area; however, participants reported higher levels of stability and lower levels of exertion with hip belt use. Load placement did not affect average velocity, sway area, perceived stability or exertion. This study showed that wearing a backpack loaded to 20% of body weight reduced postural stability, while manipulation of load placement in a backpack did not affect subjective and objective measures of postural stability. Also, hip belt use only improved subjective measures of postural stability.     

Maintaining and modifying pace through tactile and multimodal feedback

Older adults are recommended to remain physically active to reduce the risk of chronic diseases and to maintain psychological well-being. At the same time, research also suggests that levels of fitness can be raised among this group. This paper describes the development and evaluation of a mobile technology, which enables older adults to monitor and modify their walking habits, with the long-term aim of sustaining appropriate levels of physical activity. An empirical study was conducted with twenty older adults to determine the feasibility of the proposed solution, with results indicating that tactile signals could be perceived while in motion and could support participants in walking at a range of paces. However, the effects were difficult to discern due to limitations of the hardware. In response, a novel low-cost prototype was developed to amplify vibrations, and effectiveness of redundant auditory information was investigated with the goal of enhancing the perception of the cues. A second study was conducted to determine the impact of multimodal feedback on walking behavior. Findings revealed that participants were able to maintain a desired level of pace more consistently when redundant auditory information was presented alongside the tactile feedback. When the visual channel is not available, these results suggest that tactile cues presented via a mobile device should be augmented with auditory feedback. Our research also suggests that mobile devices could be made more effective for alternative applications if they are designed to allow for stronger tactile feedback.     

A wireless embedded tongue tactile biofeedback system for balance control

We describe the architecture of an original biofeedback system for balance improvement for fall prevention and present results of a feasibility study. The underlying principle of this biofeedback consists of providing supplementary information related to foot sole pressure distribution through a wireless embedded tongue-placed tactile output device.Twelve young healthy adults voluntarily participated in this experiment. They were asked to stand as immobile as possible with their eyes closed in two conditions of no-biofeedback and biofeedback. Centre of foot pressure (CoP) displacements were recorded using a force platform. Results showed reduced CoP displacements in the biofeedback relative to the no-biofeedback condition.On the whole, the present findings evidence the effectiveness of this system in improving postural control on young healthy adults. Further investigations are needed to strengthen the potential clinical value of this device.     

Control and perception of balance at elevated and sloped surfaces

Understanding roof-work-related risk of falls and developing low-cost, practical engineering controls for reducing this risk remain in high demand in the construction industry. This study investigated the effects of the roof work environment characteristics of surface slope, height, and visual reference on standing balance in construction workers. The 24 participants were tested in a laboratory setting at 4 slopes (0 degrees, 18 degrees, 26 degrees, and 34 degrees), 2 heights (0, 3 m), and 2 visual conditions (with and without visual references). Postural sway characteristics were calculated using center of pressure recordings from a force platform. Workers' perceptions of postural sway and instability were also evaluated. The results indicated that slope and height synergistically increased workers' standing postural instability. Workers recognized the individual destabilizing effects of slope and height but did not recognize the synergistic effect of the two. Visual references significantly reduced the destabilizing effects of height and slope. Actual and potential applications of this research include the use of temporary level work surfaces and proximal vertical reference structures as postural instability control measures during roofing work.     

Microclimate in ski boots – Temperature,relative humidity,and water absorption

Ski boot quality is determined by mechanical properties and comfort. Comfort is strongly affected by cold feet. The purpose of this study was to determine the microclimate in ski boots. Climate chamber tests with five male subjects and field tests with two male subjects were conducted. Temperature and relative humidity were measured using four sensors placed on the foot and one on the liner. Absorbed water in liners and socks was measured with a precision balance. The subjects gave subjective ratings for comfort. The toe sensor temperature dropped below 20 °C at an ambient temperature of 0 °C, −10 °C, and −20 °C. Relative humidity values at the foot were as high as 78% in the climate chamber and 93% in the field. Water absorption in socks and liners ranged from 4 to 10 g in the climate chamber and 19 to 45.5 g in the field. The results reveal the importance of keeping the feet and in particular the toes warm during skiing. One possible improvement may be to construct the liner so that sweat and melted snow are kept as far away as possible from the foot. Liner material with high water absorption capacity and hydrophobic socks were suggested to prevent wet feet.     

Physical load handling and listening comprehension effects on balance control

The purpose of this study was to determine the physical load handling and listening comprehension effects on balance control. A total of 16 young and 16 elderly participants were recruited in this study. The physical load handling task required holding a 5-kg load in each hand with arms at sides. The listening comprehension task involved attentive listening to a short conversation. Three short questions were asked regarding the conversation right after the testing trial to test the participants' attentiveness during the experiment. Balance control was assessed by centre of pressure-based measures, which were calculated from the force platform data when the participants were quietly standing upright on a force platform. Results from this study showed that both physical load handling and listening comprehension adversely affected balance control. Physical load handling had a more deleterious effect on balance control under the listening comprehension condition vs. no-listening comprehension condition. Based on the findings from this study, interventions for the improvement of balance could be focused on avoiding exposures to physically demanding tasks and cognitively demanding tasks simultaneously. STATEMENT OF RELEVANCE: Findings from this study can aid in better understanding how humans maintain balance, especially when physical and cognitive loads are applied. Such information is useful for developing interventions to prevent fall incidents and injuries in occupational settings and daily activities.     

Feet kinematics upon slipping discriminate between recoveries and three types of slip-induced falls

This study investigated the relationship between feet kinematics upon slipping while walking and the outcome of the slip. Seventy-one slips (induced by walking over an unexpectedly slippery surface) were analysed, which included 37 recoveries, 16 feet-split falls, 11 feet-forward falls and seven lateral falls. Feet kinematics differed between recoveries and three types of slip-induced falls, and a discriminant model including six measures of feet kinematics correctly predicted 87% of slip outcomes. Two potentially modifiable characteristics of the feet kinematics upon slipping that can improve the likelihood of successfully averting a fall were identified: (1) quickly arresting the motion of the slipping foot and (2) a recovery step that places the trailing toe approximately 0–10% body height anterior to the sacrum. These results may inform the development of task-specific balance training interventions that promote favourable recovery responses to slipping.

Practitioner Summary: This study investigated the relationship between feet movements upon slipping and outcomes of the slip. Potentially modifiable characteristics that can reduce the likelihood of falling were: (1) quickly arresting slipping foot motion and (2) a recovery step that places the trailing toe approximately 0–10% body height anterior to the sacrum.     

The habituation of human postural responses to platform perturbations

The purpose of this study was to examine habituation and task on adaptation of postural responses to simulated wave-induced ship motions. Twenty-four participants (12 male and 12 female) performed four different tasks while being exposed to five platform motion profiles during two testing periods. The four tasks performed were: standing feet parallel stance, standing with feet in an in-step stance, holding of a 10 kg load, sagittal lifting/lowering of a 10 kg load. Motion induced correction (MIC) occurrence, corresponding platform motion parameters, and total time spent performing MICs were compared between trials and tasks. It was found that the number of MIC events and total time spent performing MICs differed significantly between trials, with the first trial for participants having more MIC events and more time spent performing postural corrections. The number of MIC events was reduced and total postural correction times were significantly quicker on the second day of testing. Results revealed significant differences in pitch and roll velocities between in-step and parallel standing and significant differences in pitch and roll accelerations between both standing tasks and MMH tasks (p < 0.05). These results suggest that MIC initiation is significantly affected by previous exposure, habituation to comparable platform motions, and task. Differences between tasks suggest that perturbation characteristics of MIC occurrence are potentially affected by shape of the base of support and additional load. These results could help explain difficulties in previous attempts to predict MIC occurrences purely upon platform motion characteristics.Relevance to industryThe results of this research suggest that when working in moving environments adaptation to motions may occur much faster than expected. Further adaptation may also occur after leaving the moving environment. These factors must be considered when evaluating offshore occupations.