492 research outputs found
Visual mental imagery during caloric vestibular stimulation.
We investigated high-resolution mental imagery and mental rotation, while the participants received caloric vestibular stimulation. High-resolution visual mental imagery tasks have been shown to activate early visual cortex, which is deactivated by vestibular input. Thus, wepredicted that vestibular stimulation would disrupt high-resolution mental imagery; this prediction was confirmed. In addition, mental rotationtasks have been shown to activate posterior parietal cortex, which is also engaged in the processing of vestibular stimulation. As predicted,we also found that mental rotation is impaired during vestibular stimulation. In contrast, such stimulation did not affect performance of alow-imagery control task. These data document previously unsuspected interactions between the vestibular system and the high-level visualsystem
Spatially Heterogeneous Effects of a Public Works Program
Most research on labor market effects of the Mahatma Gandhi National Rural Employment Guarantee Scheme focuses on outcomes at the district level. This paper shows that such a focus masks substantial spatial heterogeneity: treated villages located near untreated areas see smaller increases in casual wages than treated villages located farther from untreated areas. I argue that worker mobility, rather than spatial differences in implementation or program leakages, drives this spatial heterogeneity. I also present evidence that the effects of the program on private-sector employment display similar intra-district heterogeneity. Finally, by exploiting the difference in wage changes over space, I show that a large portion of consumption increases are driven by wage increases, not program employment. Overall, these results suggest that a district-level focus underestimates the true effect of the program on wages and also support the argument that increasing rural wages is an effective poverty-fighting tool in developing countries
Spatially Heterogeneous Effects of a Public Works Program
Most research on labor market effects of the Mahatma Gandhi National Rural Employment Guarantee Scheme focuses on outcomes at the district level. This paper shows that such a focus masks substantial spatial heterogeneity: treated villages located near untreated areas see smaller increases in casual wages than treated villages located farther from untreated areas. I argue that worker mobility, rather than spatial differences in implementation or program leakages, drives this spatial heterogeneity. I also present evidence that the effects of the program on private-sector employment display similar intra-district heterogeneity. Finally, by exploiting the difference in wage changes over space, I show that a large portion of consumption increases are driven by wage increases, not program employment. Overall, these results suggest that a district-level focus underestimates the true effect of the program on wages and also support the argument that increasing rural wages is an effective poverty-fighting tool in developing countries
The role of vestibular cues in postural sway
Controlling posture requires continuous sensory feedback about body motion and orientation, including from the vestibular organs. Little is known about the role of tilt vs. translation vs. rotation vestibular cues. We examined whether intersubject differences in vestibular function were correlated with intersubject differences in postural control. Vestibular function was assayed using vestibular direction-recognition perceptual thresholds, which determine the smallest motion that can be reliably perceived by a subject seated on a motorized platform in the dark. In study A, we measured thresholds for lateral translation, vertical translation, yaw rotation, and head-centered roll tilts. In study B, we measured thresholds for roll, pitch, and left anterior-right posterior and right anterior-left posterior tilts. Center-of-pressure (CoP) sway was measured in sensory organization tests (study A) and Romberg tests (study B). We found a strong positive relationship between CoP sway and lateral translation thresholds but not CoP sway and other thresholds. This finding suggests that the vestibular encoding of lateral translation may contribute substantially to balance control. Since thresholds assay sensory noise, our results support the hypothesis that vestibular noise contributes to spontaneous postural sway. Specifically, we found that lateral translation thresholds explained more of the variation in postural sway in postural test conditions with altered proprioceptive cues (vs. a solid surface), consistent with postural sway being more dependent on vestibular noise when the vestibular contribution to balance is higher. These results have potential implications for vestibular implants, balance prostheses, and physical therapy exercises.NEW & NOTEWORTHY Vestibular feedback is important for postural control, but little is known about the role of tilt cues vs. translation cues vs. rotation cues. We studied healthy human subjects with no known vestibular pathology or symptoms. Our findings showed that vestibular encoding of lateral translation correlated with medial-lateral postural sway, consistent with lateral translation cues contributing to balance control. This adds support to the hypothesis that vestibular noise contributes to spontaneous postural sway
Vestibular Perception following Acute Unilateral Vestibular Lesions.
Little is known about the vestibulo-perceptual (VP) system, particularly after a unilateral vestibular lesion. We investigated vestibulo-ocular (VO) and VP function in 25 patients with vestibular neuritis (VN) acutely (2 days after onset) and after compensation (recovery phase, 10 weeks). Since the effect of VN on reflex and perceptual function may differ at threshold and supra-threshold acceleration levels, we used two stimulus intensities, acceleration steps of 0.5°/s(2) and velocity steps of 90°/s (acceleration 180°/s(2)). We hypothesised that the vestibular lesion or the compensatory processes could dissociate VO and VP function, particularly if the acute vertiginous sensation interferes with the perceptual tasks. Both in acute and recovery phases, VO and VP thresholds increased, particularly during ipsilesional rotations. In signal detection theory this indicates that signals from the healthy and affected side are still fused, but result in asymmetric thresholds due to a lesion-induced bias. The normal pattern whereby VP thresholds are higher than VO thresholds was preserved, indicating that any 'perceptual noise' added by the vertigo does not disrupt the cognitive decision-making processes inherent to the perceptual task. Overall, the parallel findings in VO and VP thresholds imply little or no additional cortical processing and suggest that vestibular thresholds essentially reflect the sensitivity of the fused peripheral receptors. In contrast, a significant VO-VP dissociation for supra-threshold stimuli was found. Acutely, time constants and duration of the VO and VP responses were reduced - asymmetrically for VO, as expected, but surprisingly symmetrical for perception. At recovery, VP responses normalised but VO responses remained shortened and asymmetric. Thus, unlike threshold data, supra-threshold responses show considerable VO-VP dissociation indicative of additional, higher-order processing of vestibular signals. We provide evidence of perceptual processes (ultimately cortical) participating in vestibular compensation, suppressing asymmetry acutely in unilateral vestibular lesions
Improving Sensorimotor Function and Adaptation using Stochastic Vestibular Stimulation
Astronauts experience sensorimotor changes during adaption to G-transitions that occur when entering and exiting microgravity. Post space flight, these sensorimotor disturbances can include postural and gait instability, visual performance changes, manual control disruptions, spatial disorientation, and motion sickness, all of which can hinder the operational capabilities of the astronauts. Crewmember safety would be significantly increased if sensorimotor changes brought on by gravitational changes could be mitigated and adaptation could be facilitated. The goal of this research is to investigate and develop the use of electrical stochastic vestibular stimulation (SVS) as a countermeasure to augment sensorimotor function and facilitate adaptation. For this project, SVS will be applied via electrodes on the mastoid processes at imperceptible amplitude levels. We hypothesize that SVS will improve sensorimotor performance through the phenomena of stochastic resonance, which occurs when the response of a nonlinear system to a weak input signal is optimized by the application of a particular nonzero level of noise. In line with the theory of stochastic resonance, a specific optimal level of SVS will be found and tested for each subject [1]. Three experiments are planned to investigate the use of SVS in sensory-dependent tasks and performance. The first experiment will aim to demonstrate stochastic resonance in the vestibular system through perception based motion recognition thresholds obtained using a 6-degree of freedom Stewart platform in the Jenks Vestibular Laboratory at Massachusetts Eye and Ear Infirmary. A range of SVS amplitudes will be applied to each subject and the subjectspecific optimal SVS level will be identified as that which results in the lowest motion recognition threshold, through previously established, well developed methods [2,3,4]. The second experiment will investigate the use of optimal SVS in facilitating sensorimotor adaptation to system disturbances. Subjects will adapt to wearing minifying glasses, resulting in decreased vestibular ocular reflex (VOR) gain. The VOR gain will then be intermittently measured while the subject readapts to normal vision, with and without optimal SVS. We expect that optimal SVS will cause a steepening of the adaptation curve. The third experiment will test the use of optimal SVS in an operationally relevant aerospace task, using the tilt translation sled at NASA Johnson Space Center, a test platform capable of recreating the tilt-gain and tilt-translation illusions associated with landing of a spacecraft post-space flight. In this experiment, a perception based manual control measure will be used to compare performance with and without optimal SVS. We expect performance to improve in this task when optimal SVS is applied. The ultimate goal of this work is to systematically investigate and further understand the potential benefits of stochastic vestibular stimulation in the context of human space flight so that it may be used in the future as a component of a comprehensive countermeasure plan for adaptation to G-transitions
Exhibition of Stochastic Resonance in Vestibular Perception
Astronauts experience sensorimotor changes during spaceflight, particularly during G-transitions. Post flight sensorimotor changes include spatial disorientation, along with postural and gait instability that may degrade operational capabilities of the astronauts and endanger the crew. A sensorimotor countermeasure that mitigates these effects would improve crewmember safety and decrease risk. The goal of this research is to investigate the potential use of stochastic vestibular stimulation (SVS) as a technology to improve sensorimotor function. We hypothesize that low levels of SVS will improve sensorimotor perception through the phenomenon of stochastic resonance (SR), when the response of a nonlinear system to a weak input signal is enhanced by the application of a particular nonzero level of noise. This study aims to advance the development of SVS as a potential countermeasure by 1) demonstrating the exhibition of stochastic resonance in vestibular perception, a vital component of sensorimotor function, 2) investigating the repeatability of SR exhibition, and 3) determining the relative contribution of the semicircular canals (SCC) and otolith (OTO) organs to vestibular perceptual SR. A constant current stimulator was used to deliver bilateral bipolar SVS via electrodes placed on each of the mastoid processes, as previously done. Vestibular perceptual motion recognition thresholds were measured using a 6-degree of freedom MOOG platform and a 150 trial 3-down/1-up staircase procedure. In the first test session, we measured vestibular perceptual thresholds in upright roll-tilt at 0.2 Hz (SCC+OTO) with SVS ranging from 0-700 A. In a second test session a week later, we re-measured roll-tilt thresholds with 0, optimal (from test session 1), and 1500 A SVS levels. A subset of these subjects, plus naive subjects, participated in two additional test sessions in which we measured thresholds in supine roll-rotation at 0.2 Hz (SCC) and upright y-translation at 1 Hz (OTO) with SVS up to 700 A. A sinusoidal galvanic vestibular stimulation (GVS) perceptual threshold was also measured on each test day and used to normalize the SVS levels across subjects. In roll-tilt thresholds with SVS, the characteristic SR curve was qualitatively exhibited in 10 of 12 subjects, and the improvement in motion threshold was significant in 6 subjects, indicating that optimal SVS improved passive body motion perception in a way that is consistent with classical SR theory. A probabilistic comparison to numeric simulations further validated these experimental results. On the second test session, 4 out of the 10 SR exhibitors showed repeated improvement with SVS compared to the no SVS condition. Data collection is ongoing for the last two test sessions in which SCC and OTO only perceptual motion recognition thresholds are being measured with SVS. The final results of these test sessions will give insight into whether vestibular perceptual SR can occur when only one type of vestibular sensor is sensing motion or if it is more evident when sensory integration between the SCC and OTO is occurring during the motion. The overall purpose of this research is to further quantify the effects of SVS on various sensorimotor tasks and to gain a more fundamental understanding of how SVS causes SR in the vestibular system. In the context of human space flight, results from this research will help in understanding how SVS may be practically implemented in the future as a component of a comprehensive countermeasure plan for G-transition adaptation
Quality of Life Associated with Physical Activity but not Sedentary Time in Youth
Purpose: It has been reported that youth who engaged in more screen time had lower quality of life scores compared to those that were more physically active. Furthermore, increased sedentary behavior increases health risks particularly the risk for obesity. A cross-sectional analysis was completed to examine the relationship between healthrelated quality-of-life (HRQOL) and accelerometer-measured sedentary time (ST) and physical activity (PA) in 9-10-yearold youth who were recruited for the family-based, childhood obesity intervention, iCook 4-H. It was hypothesized that objectively measured ST would be negatively correlated and PA would be positively correlated with HRQOL.Methods: A subset of participants (n=118) wore Actigraph GT3X+ accelerometers for 7 days and completed the Pediatric Quality of Life survey (PedsQLTM, version 4.0) to assess HRQOL. Mean daily minutes of accelerometermeasured ST (547 ± 60) and PA including light-intensity (LPA=240 ± 49), moderate-intensity (MPA=35 ± 11), vigorous-intensity (VPA=17 ± 9), and moderate-to vigorousintensity (MVPA=52 ± 19) were evaluated during waking hours. Multiple linear regressions were used to assess relationship between ST and PA intensities with HRQOL. Statistical significance was set at p ≤ 0.05.Results: There were no significant associations between ST or LPA with HRQOL. MPA, VPA and MVPA were positively associated with multiple HRQOL domains.Conclusion: The lack of relationship between objectively measured ST and LPA with the total HRQOL score and subscales merits further investigation. The findings of the current study support the need for lifestyle interventions that engage families in behavior that increases MVPA
The iCook 4-H Study: Report on Physical Activity and Sedentary Time in Youth Participating in a Multicomponent Program Promoting Family Cooking, Eating, and Playing Together
Objective To report physical activity and sedentary time outcomes of youth in iCook 4-H. Study Design and Setting iCook 4-H was a 5-state, randomized, control–treatment, family-based childhood obesity prevention intervention promoting cooking, eating, and playing together. Participants and Intervention Youth aged 9–10 years and the main preparer of their meals participated in the 12-week program followed by monthly newsletters and biyearly booster sessions until 24 months. Main Outcome Measure(s) A total of 155 youth were fitted with an Actigraph GT3X+ accelerometer, which they wore for 7 days at baseline and 4, 12, and 24 months to measure mean daily minutes per hour of waking wear time for sedentary time (ST), light physical activity (PA) (LPA), moderate PA, vigorous PA, and moderate to vigorous PA. Self-reported PA was assessed using the Block Kids Physical Activity Screener and additional questions querying for the program goal of the frequency of family actively playing together. Linear mixed models were used to determine differences from baseline to 24 months. Significance was set at P ≤ .05. Results There was a significant (P \u3c .05) group × time interaction for LPA (adjusted interaction B estimate, 95% confidence interval; 0.18 [0.05, 0.30]) and ST (−0.15 [−0.26, −0.04]); ST increased and LPA decreased in the treatment group. There were no differences in other accelerometer-derived PA measures, self-report Block Kids Physical Activity Screener measures, or frequency of family actively playing together at any time point. Conclusions and Implications iCook 4-H was a multicomponent program observing youth aged 9–10 years for 24 months that focused on enhancing cooking skills, mealtime behavior and conversation, and PA through daily family activities. Greater emphasis on developing PA skills, changing environmental factors, and increasing PA both in and after school may be needed
The iCook 4-HStudy: Report on Physical Activity and Sedentary Time in Youth Participating in a Multicomponent Program Promoting Family Cooking, Eating, and Playing Together
Objective: To report physical activity and sedentary time outcomes of youth in iCook 4-H. Study Design and Setting: iCook 4-H was a 5-state, randomized, control−treatment, family-based childhood obesity prevention intervention promoting cooking, eating, and playing together. Participants and Intervention: Youth aged 9−10 years and the main preparer of their meals participated in the 12-week program followed by monthly newsletters and biyearly booster sessions until 24 months. Main Outcome Measure(s): A total of 155 youth were fitted with an Actigraph GT3X+ accelerometer, which they wore for 7 days at baseline and 4, 12, and 24 months to measure mean daily minutes per hour of waking wear time for sedentary time (ST), light physical activity (PA) (LPA), moderate PA, vigorous PA, and moderate to vigorous PA. Self-reported PA was assessed using the Block Kids Physical Activity Screener and additional questions querying for the program goal of the frequency of family actively playing together. Linear mixed models were used to determine differences from baseline to 24 months. Significance was set at P ≤ .05. Results: There was a significant (P \u3c .05) group £ time interaction for LPA (adjusted interaction B estimate, 95% confidence interval; 0.18 [0.05, 0.30]) and ST (-0.15 [-0.26, -0.04]); ST increased and LPA decreased in the treatment group. There were no differences in other accelerometer-derived PA measures, self-report Block Kids Physical Activity Screener measures, or frequency of family actively playing together at any time point. Conclusions and Implications: iCook 4-H was a multicomponent program observing youth aged 9−10 years for 24 months that focused on enhancing cooking skills, mealtime behavior and conversation, and PA through daily family activities. Greater emphasis on developing PA skills, changing environmental factors, and increasing PA both in and after school may be needed
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