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BACKGROUND: Diabetic older people tend to present deteriorated performance in balance and locomotion activities, even those without peripheral neuropathy. There is evidence that saccadic eye movements are used to reduce body sway in young and older healthy adults, but it has not been shown that diabetic older people preserve this visuomotor adaptation capacity. RESEARCH QUESTION: Are diabetic older women without peripheral neuropathy capable of improving postural stability during a saccadic gaze task? METHODS: Seventeen type 2 diabetic older women (68.2 ± 10.7 years old) and seventeen healthy women, age-matched controls (66.0 ± 8.4 years old) voluntarily participated in the study. All participants were instructed to stand upright, barefoot, as stable as possible, for 30 s. Participants maintained their feet parallel to each other, at standard and narrow bases of support, while either fixating on a stationary target (fixation condition) or performing horizontal saccadic eye movements to follow a target (eccentricity of 11° of visual angle), which continuously disappeared and reappeared immediately on the opposite side (saccade 0.5 Hz and saccade 1.1 Hz conditions). RESULTS: Results indicated that the diabetic group clearly had deteriorated postural control, as shown by increased values of mean sway amplitude and mean sway velocity. However, diabetic and control groups were similarly capable of using saccadic eye movements to improve their postural stability, reducing their sway velocity compared to a gaze fixation condition. SIGNIFICANCE: Diabetes per se (without peripheral neuropathy) amplifies postural sway of older women as compared to their healthy age-matched controls. However, diabetic older women without peripheral neuropathy are capable of improving postural stability during a saccadic gaze task.

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This study examined changes in postural control and gaze performance of faller and non-faller older adults under conditions of visual tasks and optical flow manipulations. Fifteen older non-fallers (69.8 years, ± 3.2) and fifteen older fallers (71.1 years, ± 6.4) stood on a force platform inside a moving room wearing an eye tracker. Four tasks were performed: gaze fixation; predictable saccades; unpredictable saccades; and free-viewing. The stimuli appeared at a frequency of 1.1 Hz during conditions of predictable and unpredictable saccades. Sixteen trials were divided into two blocks. In the first block, the room remained stationary. In the second block, the room oscillated, without the participant's awareness, with a 0.6 cm amplitude and 0.2 Hz frequency. Results showed postural sway attenuation in older fallers during the saccadic tasks compared to gaze fixation and free-viewing tasks, in both stationary and moving room conditions. Both groups showed increased center of pressure (CoP) magnitude during the moving room condition and CoP displacements strongly coupled to the room's movement. The influence of the moving room on the postural sway was reduced during the saccadic tasks for both older groups. Older fallers exhibited higher variability compared to older non-fallers. Gaze behavior differences between groups were dependent on the goals of the visual tasks. Therefore, CoP displacements of older adults are reduced during saccadic tasks regardless of their falling history. However, postural and gaze performance of older fallers suggests increased deterioration of postural and oculomotor control which may be used as a predictor of fall risk.

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The aim of this study was to investigate the effects of ankle and hip muscle fatigue on motor adjustments (experiment 1) and symmetry (experiment 2) of postural control during a quiet standing task. Twenty-three young adults performed a bipedal postural task on separate force platforms, before and after a bilateral ankle and hip muscle fatigue protocol (randomized). Ankle and hip muscles were fatigued separately using a standing calf raise protocol (ankle fatigue) on a step and flexion and extension of the hip (hip fatigue) sitting on a chair, at a controlled movement frequency (0.5Hz), respectively. In both experiments, force, center of pressure, and electromyography parameters were measured. The symmetry index was used in experiment 2 to analyze the postural asymmetry in the parameters. Our main findings showed that muscle fatigue impaired postural stability, regardless of the fatigued muscle region (i.e., ankle or hip). In addition, young adults used an ankle motor strategy (experiment 1) before and after both the ankle and hip muscle fatigue protocols. Moreover, we found increased asymmetry between the lower limbs (experiment 2) during the quiet standing task after muscle fatigue. Thus, we can conclude that the postural motor strategy is not muscle fatigue joint-dependent and a fatigue task increases postural asymmetry, regardless of the fatigued region (hip or ankle). These findings could be applied in sports training and rehabilitation programs with the objective of reducing the fatigue effects on asymmetry and improving balance.

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The aim of this study was to investigate the effects of wearing virtual reality head-mounted goggles (VR) on body sway in young adults. We run two experiments, in which we compared the body sway while standing during the conditions of 1) wearing and non-wearing VR with eyes-opened (experiment #1), 2) wearing and no-wearing VR with eyes-closed (experiment #2), and 3) wearing VR with eyes-opened when the scene was turned on and off (experiment #2). Forty-four (experiment #1) and fifteen (experiment #2) young adults were instructed to remain as still as possible on a force plate for 60-s and performed three trials in each quiet standing condition. The center of pressure (CoP) displacement, mean velocity, root mean square (RMS), area and median frequency of sway were calculated in both experiments. In the experiment #1, wearing VR condition with eyes-opened largely increased the AP and ML CoP displacement, AP mean velocity, AP and ML RMS, and area (p < 0.05) compared to non-wearing VR with eyes-opened. In the experiment #2, no differences were found for any conditions (eyes-closed and eyes-opened with turned on and off VR scene). In conclusion, wearing VR head-mounted goggles increased body sway of young adults during standing postural task, when the individuals were with eyes-opened. However, the effects of wearing VR head-mounted goggles on body sway disappeared when the individuals were with eyes-closed or the google scene was turned off the scene compared to not wearing VR head-mounted goggles with eyes-closed or turned on scene, respectively.

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BACKGROUND: People with Parkinson's disease (PD) do not differ from neurologically healthy individuals in obstacle circumvention during walking, therefore they are able to use visual feedback adequately to control motor behavior in this task. However, individuals are often distracted by the secondary task when circumventing an obstacle. An increased cognitive load can require prolonged gaze fixation time on a location of interest to compensate for longer information processing duration. RESEARCH QUESTION: To investigate the effects of cognitive dual tasking (DT) on gaze behavior during waking with obstacle circumvention in people with PD and control group, and to determine the impact of gaze behavior on motor strategy. METHODS: Fifteen individuals with PD (PD-group) and 15 neurologically healthy individuals walked at a self-selected speed over a walkway and circumvented an obstacle centered in the walkway. The experimental conditions (5 trials each one) included obstacle circumvention without DT (OC) and obstacle circumvention with DT (OCDT). In the cognitive task, the participant mentally counted the number of times a target number appeared in an audio recording. We analyzed gaze behavior (i.e. number of gaze fixations and duration on the ground and obstacle), standard gait measures and DT cost. Two-way ANOVAs were completed for gait parameters and moment of fixation. RESULTS: There was no significant difference in DT cost between groups and no obstacle contacts. The participants performed a longer mean duration of fixations on the ground during OCDT compared to OC. Group x condition interactions indicated that the PD-group delayed the obstacle fixation relative to the NHI for OCDT (p < 0.001) and presented greater medial-lateral body clearance (p < 0.001) and longer double support time (p < 0.001) during OCDT compared to OC. SIGNIFICANCE: The results of this study suggest that deficits in locomotion during DT in PD-group may be caused, at least in part, by a reduced ability to fixate gaze at appropriate times during walking.

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BACKGROUND: Multiple Sclerosis (MS) is a neurodegenerative and inflammatory disease that impacts both visual and postural control. It is currently unknown how the integration between visual and postural control is affected in people with MS (PwMS). It has been shown in healthy individuals that saccadic eye movements can decrease body sway as result as the integration of eye and postural movements. OBJECTIVE: Investigate the effect of saccadic eye movement on postural control in PwMS and compare with neurologically healthy people. METHODS: Thirteen mildly affected PwMS (1.53 ± 1.03 on Expanded Disability Status Scale - EDSS) and 12 healthy neurologically people participated in this study. Postural control was assessed on a force platform under two eye movement conditions: fixation on a central target and saccadic eye movement. The dependent variables assessed were the displacement, velocity, root-mean-square (RMS) and area of postural center of pressure and the number, duration, variability, fixations errors and eye response time. A mobile eye tracker was used to record eye movement. Two-way ANOVA (group and eye movement) for postural variables was performed. For the eye variables, one-way ANOVA with factor to group was performed. The p-value was maintained at 0.05 for all statistical analysis and the effect sizes were based on Cohen's d. RESULTS: No group or interaction effects (group*eye movement) were found for postural and eye variables. However, the saccadic eye movement attenuated the postural displacement in anteroposterior (AP) direction (p < 0.001, Cohen's d = 4.677), RMS AP (p < 0.001, Cohen's d = 4.399) and area (p < 0.013, Cohen's d = 2.163) in comparison with the central fixation condition in both groups. The Cohen's d showed a large effect between groups for fixation errors (d = 0.741). CONCLUSION: Both groups presented similar postural control performance in both eye movement conditions. Moreover, PwMS could attenuate body sway similarly to the control group, showing that the central integration of dynamic eye movements and postural control is preserved in mildly affected PwMS.

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The color of an obstacle may enable a more detailed view of the environment to facilitate obstacle avoidance. However, people with Parkinson's disease (PD) present visual contrast and color detection dysfunction, which could affect obstacle avoidance according to obstacle color. Thus, the aim of this study was to investigate the influence of obstacle color on locomotor and gaze behavior during obstacle avoidance in people with PD and neurologically healthy older individuals. Thirteen people with PD and eleven matched-control group individuals, with normal visual acuity (20/20 on the Snellen chart), performed 20 trials (5 trials for each obstacle color condition) of the obstacle avoidance task with the following obstacle colors: white, black, red, and blue. Participants were positioned at the beginning of a walkway with their eyes closed and, after the start command, opened their eyes, started walking at their preferred velocity, and crossed the obstacle. Spatial-temporal parameters and fixations on the obstacle (gaze behavior) were measured using a three-dimensional camera system and mobile eye-tracker, respectively. Our main findings were the absence of significant color interaction on locomotor and gaze behaviors, the absence of significant main effect of color on gaze behavior, and an effect of obstacle color on locomotor behavior, specifically in the placement of the heel from the obstacle after crossing and toe-clearance for both trailing and leading limbs, which indicates that obstacle color can play a role in obstacle avoidance during walking. However, there was no consistent obstacle color that influenced the locomotor behavior. Therefore, the conclusion of this study is that obstacle color seems to affect locomotor behavior, but not gaze behavior, during walking with obstacle avoidance in people with PD and neurologically healthy individuals. However, no particular obstacle color causes a consistent effect on locomotor behavior.

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BACKGROUND: The mechanisms that contribute to gait asymmetry in people with Parkinson's disease (PD) are unclear, mainly during gait with greater environmental demand, such as when an obstacle is circumvented while walking. OBJECTIVE: The aim of this study was to investigate the effects of obstacle circumvention of the least and most affected side on motor and gaze behavior in people with PD under/without the effects of dopaminergic medication. METHODS: Fifteen people with PD and 15 matched-control individuals were instructed to walk along a pathway, at a self-selected velocity, and to circumvent an obstacle, avoiding contact with it. Each participant performed five trials for each side. Kinematic parameters, mediolateral and horizontal body clearance to the obstacle, strategy to circumvent the obstacle, and gaze behavior were calculated. Parameters were grouped according to the side that the obstacle was circumvented and compared by three-way ANOVAs. RESULTS: Both people with PD and the control group presented asymmetry to circumvent an obstacle during walking, however this was exacerbated in people with PD. Individuals with PD presented safe strategies (largest mediolateral and horizontal body clearance to the obstacle, "lead-out" strategy, and higher number and time of fixations on the obstacle) during obstacle circumvention for the least affected side compared to the most affected side. In addition, positive effects of dopaminergic medication on body clearance, spatial-temporal parameters, and gaze behavior were evidenced only when the obstacle was circumvented to the least affected side. CONCLUSIONS: The obstacle circumvention to the most affected side is risky for people with PD.

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Postural control is influenced by eye movements. Gaze fixation, which comprises a component of ocular vergence, is important in the acquisition of highly specific task information, but its relation to postural control is little investigated. The aim of the study was to investigate the effects of gaze fixation position (central and lateral fixations) on postural sway in young adults. Forty young adults with ages ranging from 20 to 35 years were invited to participate in the study. Postural sway was measured in quiet stance in bipedal support in three 60-s trials under the following conditions: gaze fixation on a target positioned in front of participant, gaze fixation on a target positioned on right side of participant, and gaze fixation on a target positioned on left side of participant. The following center of pressure parameters (COP) in the anteroposterior (AP) and mediolateral directions (ML) were analyzed for each of the trials: body sway displacement, mean velocity of sway, root mean square (RMS) of sway, and median frequency. In addition, detrended fluctuation analysis (DFA) exponent, in anteroposterior and medio-lateral directions, was calculated. The COP presented greater AP and ML displacement (p<0.03, effect size=1.37; and p<0.03, effect size=1.64, respectively) and RMS AP and ML (p<0.04, effect size=1.66; and p<0.02, effect size=2.50, respectively) for lateral gaze fixation compared to central gaze fixation. These results suggest that gaze fixation on a laterally positioned target increases body sway in anteroposterior and mediolateral directions.

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The aim of this study was to analyze the motor and visual strategies used when walking around (circumvention) an obstacle in patients with Parkinson's disease (PD), in addition to the effects of dopaminergic medication on these strategies. To answer the study question, people with PD (15) and neurologically healthy individuals (15 - CG) performed the task of obstacle circumvention during walking (5 trials of unobstructed walking and obstacle circumvention). The following parameters were analyzed: body clearance (longer mediolateral distance during obstacle circumvention of the center of mass -CoM- to the obstacle), horizontal distance (distance of the CoM at the beginning of obstacle circumvention to the obstacle), circumvention strategy ("lead-out" or "lead-in" strategy), spatial-temporal of each step, and number of fixations, the mean duration of the fixations and time of fixations according to areas of interest. In addition, the variability of each parameter was calculated. The results indicated that people with PD and the CG presented similar obstacle circumvention strategies (no differences between groups for body clearance, horizontal distance to obstacle, or obstacle circumvention strategy), but the groups used different adjustments to perform these strategies (people with PD performed adjustments during both the approach and circumvention steps and presented greater visual dependence on the obstacle; the CG adjusted only the final step before obstacle circumvention). Moreover, without dopaminergic medication, people with PD reduced body clearance and increased the use of a "lead-out" strategy, variability in spatial-temporal parameters, and dependency on obstacle information, increasing the risk of contact with the obstacle during circumvention.

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Saccadic eye movements reduce body sway, yet visually pursuing a moving dot seems to increase body sway. However, how these two types of eye movements affect postural control remains ambiguous, particularly for smooth pursuit eye movements. The aim of this study was to examine the effects of saccade and smooth pursuit eye movements on body sway magnitude during low and high frequencies. Ten young adults (19.5 ± 1.9 years) participants were required to stand upright, barefoot for 70s using a bipedal stance, with feet hip width apart, fixating or pursuing a target that was displayed on a monitor positioned 100 cm away from their eyes. Each participant performed three trials using both types of eye movements, in particular, slow and fast saccades, and slow and fast smooth pursuit movements. Body sway was obtained using reflective markers attached to a participant's head and trunk, which were recorded by two video cameras. The results indicated that body sway was reduced during both saccadic eye movements and smooth pursuit movements when compared to fixation, independent of visual frequencies. These results suggested similarities in the control of saccades and smooth pursuit on postural control.

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Several structures of the central nervous system share involvement in both ocular and postural control, but the visual mechanisms in postural control are still unclear. There are discrepant evidences on whether saccades would improve or deteriorate stabilization of posture. The purpose of this study was to determine the influence of saccadic eye movements on postural control while standing in different basis of support. Twelve young adults stood upright in wide and narrow stances while performing fixation and saccades of low and high frequencies. Body sway was attenuated during saccades. Trunk anterior-posterior sway and trunk total displacement decreased during saccades compared to fixation; higher sway mean frequency in anterior-posterior direction during saccades was observed. Body sway was reduced in wide compared to narrow stance during high frequency saccades. These results indicate that eye movement improves postural stabilization and this effect is stronger in combination of wide stance-high frequency gaze condition.

Várias estruturas do sistema nervoso central compartilham envolvimento nos controles ocular e postural, mas os mecanismos visuais no controle postural ainda não estão claros. Existem evidências discrepantes sobre a possibilidade de movimentos sacádicos melhorarem ou deteriorarem a estabilização postural. O objetivo desse estudo foi determinar a influência de movimentos sacádicos dos olhos sobre o controle postural em diferentes bases de apoio. Doze adultos jovens ficaram em pé, mantendo a postura sobre base ampla e restrita enquanto realizavam fixações e movimentos sacádicos de baixa e alta frequência. Oscilação corporal foi atenuada durante movimentos sacádicos. A oscilação do tronco na direção ântero-posterior e o deslocamento total do tronco diminuíram durante movimentos sacádicos comparados à fixação; maior frequência média de oscilação na direção ântero-posterior durante movimentos sacádicos também foi observada. Oscilação corporal foi reduzida em postura com base ampla comparada à restrita durante movimentos sacádicos de alta frequência. Estes resultados indicam que o movimento do olho melhora a estabilização postural e este efeito é mais forte na condição que combina base ampla e alta frequência do olhar.

Varias estructuras del sistema nervioso central comparten de participación en los controles ocular y de postura. Existen pruebas dispares sobre lo movimiento sacádico mejorar o deteriorar la estabilización postural. El objetivo de este estudio fue determinar la influencia de los movimientos oculares sacádicos sobre el control postural en diferentes bases de apoyo. Doce jóvenes quedaram de pie manteniendo la postura de base amplia y restringido mientras hacian fijaciones y movimientos sacádicos de baja y alta frecuencia. Lal oscilación del cuerpo fue atenuada durante los movimientos sacádicos. La oscilación del tronco en dirección antero-posterior y el desplazamiento total del tronco han disminuido durante los movimientos sacádicos comparados con fijación; también se ha observado mayor frecuencia media de oscilación en la dirección anteroposterior durante los movimientos sacádicos. La oscilación del cuerpo se redujo por la postura de base amplia en comparación con la restringida durante los movimientos sacádicos de alta frecuencia. Estos resultados indican que lo movimiento de ojo mejora la estabilización postural y este efecto es más fuerte para la condición de base amplia y alta frecuencia de la mirada.

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O objetivo deste estudo foi avaliar o processo de aprendizagem motora de uma habilidade complexa da Ginástica Artística a partir da observação de demonstrações de modelos de pontos de luz e vídeo. Dezesseis participantes divididas em grupos dos respectivos modelos executaram um pré-teste, seguido de 100 tentativas de uma parada de mãos, igualmente distribuídas em blocos de 10 tentativas em dois dias, alternando períodos de demonstração e prática, com um teste de retenção após um dia. Cinemática de braço, tronco e perna das participantes possibilitaram análise da semelhança entre a coordenação de cada participante e do modelo e do tempo de movimento; a performance das participantes também foi avaliada por duas especialistas em Ginástica Artística. Ambas as análises indicaram que os grupos não diferiram. Os resultados são discutidos em termos da hipótese de suficiência de informação nos modelos de movimento biológico particularmente aplicada ao processo de aprendizagem de habilidades motoras complexas.

The aim of this study was to evaluate the motor learning process of a complex Artistic Gymnastics skill following demonstrations of point-light and video models. Sixteen participants divided into the respective model groups performed a pre-test and 100 trials of a handstand, equally distributed in blocks of 10 trials in two days, alternating periods of demonstration and practice, with retention test a day later. Participants' kinematics of arm, trunk, and leg was used to analyze the coordination similarities between each participant and the model and movement time; participants' performance was also evaluated by two Artistic Gymnastics experts. Both analyses revealed that the groups did not differ. Results are discussed in terms of the hypothesis of information sufficiency in biological motion models particularly applied to the learning process of complex motor skills.

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O controle visual da freada foi estudado em ciclistas recreacionais através da manipulação da velocidade no início da freada (baixa, média e alta) e da trajetória de aproximação (retilínea e curvilínea) da bicicleta em relação a um obstáculo estacionário. A hipótese foi que o tipo de trajetória da bicicleta, de modo exclusivo ou em interação com a velocidade inicial, afetaria a informação visual de tempo para colisão ("tau" margem) e sua primeira derivada no tempo ("tau-dot"), respectivamente, no início e durante a freada. Os resultados revelaram que a velocidade afetou significativamente "tau" margem, enquanto "tau-dot" manteve-se inalterado independentemente da condição. O tipo de trajetória claramente não afetou o controle visual da freada em ciclistas.

Braking visual control was studied in recreational cyclists through the manipulation of bicycle's velocity at braking initiation (low, medium, and high) and approaching trajectory (straight and curved) with respect to a stationary obstacle. The hypothesis was that the type of trajectory, exclusively or interacting with initial velocity, would affect time to collision visual information (tau margin) and its first derivative in time (tau-dot), respectively, in the onset and during braking. The results revealed that velocity affected significantly tau margin while tau-dot remained unaltered independently of condition. The type of trajectory clearly did not affect the visual control of braking in cyclists.

El control visual de la frenada fue estudiado en ciclistas recreativos mediante la manipulación de la velocidad (baja, media y alta) al principio de la frenada y la trayectoria de aproximación de la bicicleta (rectilínea y curvilínea) en relación con un obstáculo fijo. La hipótesis era que el tipo de trayectoria de la bicicleta, de modo exclusivo o en interacción con la velocidad inicial, afectaría la información visual del momento de la colisión (margen "tau") y su primera derivada en el tiempo ("tau-dot"), respectivamente, al principio y durante la frenada. Los resultados revelaron que la velocidad afectó significativamente el margen "tau", mientras que el "tau-dot" permaneció inalterado independientemente de su condición. El tipo de trayectoria claramente no afectó el control visual de frenado en los ciclistas.

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