The effects of optic flow on postural stability: Influence of age and fall risk.

BACKGROUND: Optic flow provides dynamic information relating to body position and motion with respect to visual frames of reference. This study investigated the effects of optic flow stimuli presented in four directions on postural stability in young and older adults. METHODS: Twenty-five young (20-40 years) and 51 older (≥65 years) people participated in this study, with the older group classified into low fall risk (n = 27), and high fall risk (n = 24) sub-groups. While standing in a dark room, participants viewed static scattered white dots for 30 s, followed by 30 s periods of optic flow consisting of white dots "moving" in one of four flow directions, randomised: radial expansion and contraction, circular anti-clockwise and clockwise. Centre of pressure (CoP) position, postural sway in anteroposterior (AP) and mediolateral (ML) axes, and muscle activity of tibialis anterior (TA), gastrocnemius medialis (GM) and tensor fascia latae (TFL) were recorded. RESULTS: Across groups, the four optic flow stimuli induced increased AP sway and three of the four optic flow stimuli induced increased ML sway, with concomitant increases in muscle activity, indicating optic flow stimuli induced a generalised destabilising, rather than a direction-specific, effect. Only one optic flow condition (radial contraction) induced a change in average CoP position, and this may reflect the adoption of a protective stance position to avoid a backward fall. Optic flow destabilised postural control more in older people compared with younger people, and radial expansion stimuli destabilised ML postural control more in the older high fall risk group compared with the older low fall risk group. CONCLUSION: Optic flow stimuli have a generalised destabilising effect on postural control across groups as shown by non-directional specific increases in postural sway and muscular activity. Optic flow stimuli have a greater impact on postural stability in older compared with younger adults and this is more pronounced in the ML plane for older people at increased risk of falls.

Osteopathy students profile in Italy: A cross sectional census.

INTRODUCTION: The Osteopathy Students Analysis (OSA) aims to profile osteopathy students in Italy as a target population in terms of sociodemographic characteristics, geographical distribution, health status, and previous and ongoing education specifications. MATERIALS AND METHODS: The OSA used a cross-sectional design. A Web-based survey was distributed to the Italian Osteopathic Education Institutions (OEIs). The OSA survey was composed of items organised into four sections: 1. Sociodemographic characteristics (11 items); 2. Geographical distribution (5 items); 3. Health status (3 items); 4. Previous and ongoing education specifications (16 items). A descriptive sample population analysis was performed. Dichotomous and categorical variables were presented as frequencies and percentages, and continuous variables were displayed as means and standard deviations. Some variables were analysed using a pentenary distribution. RESULTS: 49 out of the 61 OEIs identified matched the inclusion criteria, and among these, 22 accepted to propose the enrolment of their students into the study. The survey was administered to 4,720 students from all the participant OEIs. A total of 3,762 students responded to the survey, accounting for an estimated response rate of 53.7%. The majority of respondents were men (54%), with an average age of 26.9 ± 6.5 years. Almost the totality of the sample was composed of the European ethnic group (99.1%). Respondents were predominantly born in Italy (97.2%). The majority of the sample reported being in good (49.5%) to excellent (38.6%) health. To date, osteopathy students are almost evenly distributed between the two types of curricula (T1 = 46.6%; T2 = 53.4%). CONCLUSIONS: The OSA is the first study that aims to profile Italian osteopathy students as a target population in terms of sociodemographic characteristics, geographical distribution, health status, and previous and ongoing education specifications. Future studies should focus on investigating the correlation between the sociodemographic characteristics of students and their academic performance.

Angle of gaze and optic flow direction modulate body sway.

Optic flow is a crucial signal in maintaining postural stability. We sought to investigate whether the activity of postural muscles and body sway was modulated by eye position during the view of radial optic flow stimuli. We manipulated the spatial distribution of dot speed and the fixation point position to simulate specific heading directions combined with different gaze positions. The experiments were performed using stabilometry and surface electromyography (EMG) on 24 right-handed young, healthy volunteers. Center of pressure (COP) signals were analyzed considering antero-posterior and medio-lateral oscillation, COP speed, COP area, and the prevalent direction of oscillation of body sway. We found a significant main effect of body side in all COP parameters, with the right body side showing greater oscillations. The different combinations of optic flow and eye position evoked a non-uniform direction of oscillations in females. The EMG analysis showed a significant main effect for muscle and body side. The results showed that the eye position modulated body sway without changing the activity of principal leg postural muscles, suggesting that the extraretinal input regarding the eye position is a crucial signal that needs to be integrated with perceptual optic flow processing in order to control body sway.

Effect of heading perception on microsaccade dynamics.

The present study shows the relationship between microsaccades and heading perception. Recent research demonstrates that microsaccades during fixation are necessary to overcome loss of vision due to continuous stimulation of the retinal receptors, even at the potential cost of a decrease in visual acuity. The goal of oculomotor fixational mechanisms might be not retinal stabilization, but controlled image motion adjusted to be optimal for visual processing. Thus, patterns of microsaccades may be exploited to help to understand the oculomotor system, aspects of visual perception, and the dynamics of visual attention. We presented an expansion optic flow in which the dot speed simulated a heading directed to the left or to the right of the subject, who had to signal the perceived heading by making a saccade toward the perceived direction. We recorded microsaccades during the optic flow stimulation to investigate their characteristics before and after the response. The time spent on heading perception was similar between right and left direction, and response latency was shorter during correct than incorrect responses. Furthermore, we observed that correct heading perception is associated with longer, larger and faster microsaccade characteristics. The time-course of microsaccade rate shows a modulation across the perception process similar to that seen for other local perception tasks, while the main direction is oriented toward the opposite side with respect to the perceived heading. Microsaccades enhance visual perception and, therefore, represent a fundamental motor process, with a specific effect for the build-up of global visual perception of space.

Wearable pendant device monitoring using new wavelet-based methods shows daily life and laboratory gaits are different.

Morbidity and falls are problematic for older people. Wearable devices are increasingly used to monitor daily activities. However, sensors often require rigid attachment to specific locations and shuffling or quiet standing may be confused with walking. Furthermore, it is unclear whether clinical gait assessments are correlated with how older people usually walk during daily life. Wavelet transformations of accelerometer and barometer data from a pendant device worn inside or outside clothing were used to identify walking (excluding shuffling or standing) by 51 older people (83 ± 4 years) during 25 min of 'free-living' activities. Accuracy was validated against annotated video. Training and testing were separated. Activities were only loosely structured including noisy data preceding pendant wearing. An electronic walkway was used for laboratory comparisons. Walking was classified (accuracy ≥97 %) with low false-positive errors (≤1.9%, κ ≥ 0.90). Median free-living cadence was lower than laboratory-assessed cadence (101 vs. 110 steps/min, p < 0.001) but correlated (r = 0.69). Free-living step time variability was significantly higher and uncorrelated with laboratory-assessed variability unless detrended. Remote gait impairment monitoring using wearable devices is feasible providing new ways to investigate morbidity and falls risk. Laboratory-assessed gait performances are correlated with free-living walks, but likely reflect the individual's 'best' performance.

Laterality of Stance during Optic Flow Stimulation in Male and Female Young Adults.

During self-motion, the spatial and temporal properties of the optic flow input directly influence the body sway. Men and women have anatomical and biomechanical differences that influence the postural control during visual stimulation. Given that recent findings suggest a peculiar role of each leg in the postural control of the two genders, we investigated whether the body sway during optic flow perturbances is lateralized and whether anteroposterior and mediolateral components of specific center of pressure (COP) parameters of the right and left legs differ, reexamining a previous experiment (Raffi et al. (2014)) performed with two, side-by-side, force plates. Experiments were performed on 24 right-handed and right-footed young subjects. We analyzed five measures related to the COP of each foot and global data: anteroposterior and mediolateral range of oscillation, anteroposterior and mediolateral COP velocity, and sway area. Results showed that men consistently had larger COP parameters than women. The values of the COP parameters were correlated between the two feet only in the mediolateral axis of women. These findings suggest that optic flow stimulation causes asymmetry in postural balance and different lateralization of postural controls in men and women.

New Methods to Monitor Stair Ascents Using a Wearable Pendant Device Reveal How Behavior, Fear, and Frailty Influence Falls in Octogenarians.

GOALS: To investigate if the stair negotiation by older people during activities of daily life (ADL) can be accurately identified using a freely worn pendant device. To investigate how usual stair-ascent performances during ADL relate to clinical assessments and prospective falls. METHODS: ADL were recorded for 30 min by 52 community-dwelling older people (83 ± 4 years) using a small pendant device. Classification accuracy was assessed using annotated video and four-fold cross validation. Correlations between sensor-derived stair-ascent features (comprising intensity, variability, and stability) and a battery of clinical tests (comprising physiological, psychological, health, and follow-up falls) were investigated. RESULTS: Accurate identification of stair events (99.8%, Kappa 0.92) was possible in both "frail" and "athletic" participants by scaling the barometer threshold to stair cadences. Cautious double-stepping strategy could be identified remotely. Stair-ascent performance was correlated with ascent strategy ( r = -0.67), age ( r = -0.44), concern about falling ( r = -0.43 ), fall-risk scores ( r = -0.41), processing speed ( r = -0.38), and contrast sensitivity ( r = 0.32). Follow-up falls were correlated with ascent stability ( r = -0.35). CONCLUSION: Remote analysis of stair ascents is feasible. In our healthy older people, outcomes appeared more related to mental rather than physiological factors. The ascent strategies we observed in some older people may have reflected an appropriate behavioral response to increased concerns about falling. SIGNIFICANCE: Given acceptance of wearable devices is increasing; reduced functional performance and altered strategies for undertaking ADL could soon be routinely tracked to augment health care.

Microsaccades and Prediction of a Motor Act Outcome in a Dynamic Sport Situation.

PURPOSE: Microsaccades could indicate the place where our mind is unconsciously focusing, although our gaze is directed elsewhere. Many studies report the importance of microsaccades in visual scene perception, but none of them has addressed their relationship with the perception of a dynamic action and the prediction of its outcome. METHODS: Expert and novice table tennis players were asked to fixate their gaze on a precise spot while viewing the launch of a ball whose final landing had to be predicted. Four separate epochs of the action were considered for their information content. The correctness of the prediction and microsaccade statistics were measured in order to estimate the relationship between covert attention and predictions. RESULTS: Microsaccades rate showed a time course modulated by the different epochs, with a significant enhancement during the post-bounce. In this epoch, novices showed a significantly higher rate than experts when the responses were correct. Duration and amplitude were highest in the pre- and post-bounce periods and lowest in the other two. Mean microsaccades direction was toward the stimuli that most probably attracted the visual attention (ball or racket), whereas there was no relationship with the predicted side of the final bounce. CONCLUSIONS: Distribution of microsaccades can be influenced by attentional cues in a task-specific situation, revealing links between visuomotor performance and covert attention shifts in fast visuomotor perception. Microsaccade orientation is conditioned by objects that attract visual attention and not by the direction in which action is expected to be performed.

Peripheral heart action (PHA) training as a valid substitute to high intensity interval training to improve resting cardiovascular changes and autonomic adaptation.

PURPOSE: The present study evaluated the effects of peripheral heart action training compared with high intensity interval training on changes in autonomic regulation and physical fitness. METHODS: Eighteen young adults (9 women, 9 men) (age 24 ± 3 years, BMI of 22.67 kg/m(2), V'O2max 32.89 ml/kg/min) were randomly assigned to either a high intensity interval training group (n = 8) or a peripheral heart action training (PHA) group (n = 10). Before and after training, maximal whole-body muscular strength, time series of beat-to-beat intervals for heart rate variability, and baroreflex sensitivity were recorded. Arterial baroreflex sensitivity and heart rate variability were estimated on both time and frequency domains. Physical fitness level was evaluated with maximum oxygen consumption test. RESULTS: The effects of PHA whole-body resistance training increased muscular strength and maximum oxygen consumption, with an effect on vagal-cardiac control and cardiovagal baroreflex sensitivity. CONCLUSIONS: After 30 training sessions performed in 3 months, PHA resistance exercise promoted cardiovascular adaptations, with a decrease in the power spectral component of vascular sympathetic activity and an increase in the vagal modulation. Low-frequency oscillation estimated from systolic blood pressure variability seems to be a suitable index of the sympathetic modulation of vasomotor activity. This investigation also want to emphasize the beneficial effects of this particular resistance exercise training, considering also that the increase in muscular strength is inversely associated with all-cause mortality and the prevalence of metabolic syndrome, independent of cardiorespiratory fitness levels.

Optic flow neurons in area PEc integrate eye and head position signals.

Neurons in area PEc, a visual area located in the superior parietal lobule, are activated by optic flow stimuli. An important issue is whether PEc neurons are able to integrate multimodal signals, such as those related to optic flow selectivity with those about eye and head position. The aim of this study was to assess if angle of gaze and/or head rotation modify the spatial representation of the focus of expansion (FOE), varying FOE, fixation point and head position in space. We found that the rotation of head modulated the firing activity of PEc optic flow neurons. The head position also changed the angle of gaze effect on the PEc neuronal activity. All recorded neurons showed a main interaction effect between head and eye position upon the selectivity for optic flow stimuli. These results seem to suggest that PEc optic flow neurons use different reference frames depending on the position of the eye and/or the head in space emphasizing a possible contribution of this area in guiding locomotion by integrating multiple extraretinal inputs.

Importance of optic flow for postural stability of male and female young adults.

PURPOSE: A feedback control process based on self-motion perception contributes to postural stability; however, little is known about the visual modulation of postural muscles. The aim of this study was to investigate the effect of optic flow stimuli, presented full field, in the peripheral and foveal visual field, on muscular activation. Then, we assessed the correlation between optic flow, muscle activity and body sway in male and female subjects. METHODS: We used surface electromyography (EMG) and stabilometry on 24 right-handed young adults. We recorded the bilateral activation of tibialis anterior, gastrocnemius medialis, biceps femoris and vastus medialis. EMG and center of pressure (COP) signals were acquired simultaneously. EMG signal amplitude was computed as root mean square normalized by baseline. RESULTS: We found a significant effect for muscles, gender and an interaction effect of muscle by gender (ANOVA, p < 0.001). Results showed different postural alignments in males and females. The COP spatial variability during peripheral stimuli was generally reduced. The prevalent direction of oscillation evoked by peripheral stimuli was clustered, while foveal and random stimuli induced distributed and randomized directions. Also for muscle activity, we found gender differences in the prevalent oscillation distributions evoked by optic flow. CONCLUSION: Visual stimuli always evoke an excitatory input on postural muscles, but the stimulus structure produces different postural effects. Peripheral optic flow stimuli stabilize postural sway, while random and foveal optic flow provoke larger sway variability similar to those evoked in the absence of visual stimulation.