Children's postural sway in response to low- and high-frequency visual information for oscillation

From silos to synergy: Integrating approaches to investigate the role of prior knowledge and expectations on episodic memory

Significant progress in the investigation of how prior knowledge influences episodic memory has been made using three sometimes isolated (but not mutually exclusive) approaches: strictly adult behavioral investigations, computational models, and investigations into the development of the system. Here we point out that these approaches are complementary, each approach informs and is informed by the other. Thus, a natural next step for research is to combine all three approaches to further our understanding of the role of prior knowledge in episodic memory. Here we use studies of memory for expectation-congruent and incongruent information from each of these often disparate approaches to illustrate how combining approaches can be used to test and revise theories from the other. This domain is particularly advantageous because it highlights important features of more general memory processes, further differentiates models of memory, and can shed light on developmental change in the memory system. We then present a case study to illustrate the progress that can be made from integrating all three approaches and highlight the need for more endeavors in this vein. As a first step, we also propose a new computational model of memory that takes into account behavioral and developmental factors that can influence prior knowledge and episodic memory interactions. This integrated approach has great potential for offering novel insights into the relationship between prior knowledge and episodic memory, and cognition more broadly.

Dynamic Visual Stimulations Produced in a Controlled Virtual Reality Environment Reveals Long-Lasting Postural Deficits in Children With Mild Traumatic Brain Injury

Motor control deficits outlasting self-reported symptoms are often reported following mild traumatic brain injury (mTBI). The exact duration and nature of these deficits remains unknown. The current study aimed to compare postural responses to static or dynamic virtual visual inputs and during standard clinical tests of balance in 38 children between 9 and 18 years-of-age, at 2 weeks, 3 and 12 months post-concussion. Body sway amplitude (BSA) and postural instability (vRMS) were measured in a 3D virtual reality (VR) tunnel (i.e., optic flow) moving in the antero-posterior direction in different conditions. Measures derived from standard clinical balance evaluations (BOT-2, Timed tasks) and post-concussion symptoms (PCSS-R) were also assessed. Results were compared to those of 38 healthy non-injured children following a similar testing schedule and matched according to age, gender, and premorbid level of physical activity. Results highlighted greater postural response with BSA and vRMS measures at 3 months post-mTBI, but not at 12 months when compared to controls, whereas no differences were observed in post-concussion symptoms between mTBI and controls at 3 and 12 months. These deficits were specifically identified using measures of postural response in reaction to 3D dynamic visual inputs in the VR paradigm, while items from the BOT-2 and the 3 timed tasks did not reveal deficits at any of the test sessions. PCSS-R scores correlated between sessions and with the most challenging condition of the BOT-2 and as well as with the timed tasks, but not with BSA and vRMS. Scores obtained in the most challenging conditions of clinical balance tests also correlated weakly with BSA and vRMS measures in the dynamic conditions. These preliminary findings suggest that using 3D dynamic visual inputs such as optic flow in a controlled VR environment could help detect subtle postural impairments and inspire the development of clinical tools to guide rehabilitation and return to play recommendations.

Perceptual-motor styles

Even for a stereotyped task, sensorimotor behavior is generally variable due to noise, redundancy, adaptability, learning or plasticity. The sources and significance of different kinds of behavioral variability have attracted considerable attention in recent years. However, the idea that part of this variability depends on unique individual strategies has been explored to a lesser extent. In particular, the notion of style recurs infrequently in the literature on sensorimotor behavior. In general use, style refers to a distinctive manner or custom of behaving oneself or of doing something, especially one that is typical of a person, group of people, place, context, or period. The application of the term to the domain of perceptual and motor phenomenology opens new perspectives on the nature of behavioral variability, perspectives that are complementary to those typically considered in the studies of sensorimotor variability. In particular, the concept of style may help toward the development of personalised physiology and medicine by providing markers of individual behaviour and response to different stimuli or treatments. Here, we cover some potential applications of the concept of perceptual-motor style to different areas of neuroscience, both in the healthy and the diseased. We prefer to be as general as possible in the types of applications we consider, even at the expense of running the risk of encompassing loosely related studies, given the relative novelty of the introduction of the term perceptual-motor style in neurosciences.

Perceiving jittering self-motion in a field of lollipops from ages 4 to 95

An internal model of self-motion provides a fundamental basis for action in our daily lives, yet little is known about its development. The ability to control self-motion develops in youth and often deteriorates with advanced age. Self-motion generates relative motion between the viewer and the environment. Thus, the smoothness of the visual motion created will vary as control improves. Here, we study the influence of the smoothness of visually simulated self-motion on an observer's ability to judge how far they have travelled over a wide range of ages. Previous studies were typically highly controlled and concentrated on university students. But are such populations representative of the general public? And are there developmental and sex effects? Here, estimates of distance travelled (visual odometry) during visually induced self-motion were obtained from 466 participants drawn from visitors to a public science museum. Participants were presented with visual motion that simulated forward linear self-motion through a field of lollipops using a head-mounted virtual reality display. They judged the distance of their simulated motion by indicating when they had reached the position of a previously presented target. The simulated visual motion was presented with or without horizontal or vertical sinusoidal jitter. Participants' responses indicated that they felt they travelled further in the presence of vertical jitter. The effectiveness of the display increased with age over all jitter conditions. The estimated time for participants to feel that they had started to move also increased slightly with age. There were no differences between the sexes. These results suggest that age should be taken into account when generating motion in a virtual reality environment. Citizen science studies like this can provide a unique and valuable insight into perceptual processes in a truly representative sample of people.

Multisensory factors in postural control: Varieties of visual and haptic effects

Background Previous work on balance control in children and adults highlights the importance of multisensory information. Work in this vein has examined two principal input sources - the role of visual and haptic information on balance. Recent work has explored the impact of a different form of haptic input - object holding - on balance in young infants. Research question This experiment examined the impact of simultaneous visual input and haptic input on balance in children and adults, employing two novel forms of haptic input. Methods Static balance was measured in 3-5 year olds, 7-9 year olds, and young adults, in the presence of all possible combinations of manipulated visual input (eyes open, eyes closed) and haptic input (no touch, object hold, touch an unstable support, touch a stable support). Results Analysis of postural stability (mean velocity) indicated that stability was influenced by visual input, haptic input, and age group. For visual input stability increased in eyes open versus eyes closed conditions. For haptic input, stability systematically increased with increasing levels of fixed haptic input (e.g., no touch, object hold, unstable touch, stable touch). Stability also increased as a function of increasing age group. There were no interactions between the factors. Significance The finding that the two novel forms of haptic input - object hold and touch with an unstable support surface - increased stability relative to no touch input, but not as much as touch with a stable support, indicates that children use haptic information in a self-referential fashion for controlling posture. The failure to observe any interactions between visual and haptic inputs with age suggests that multisensory processing is generally additive across development, and has implications for the occurrence of sensory weighting across developmental epochs.

Changes in cerebral activation in individuals with and without visual vertigo during optic flow: A functional near-infrared spectroscopy study

Background and purpose

Individuals with visual vertigo (VV) describe symptoms of dizziness, disorientation, and/or impaired balance in environments with conflicting visual and vestibular information or complex visual stimuli. Physical therapists often prescribe habituation exercises using optic flow to treat these symptoms, but it is not known how individuals with VV process the visual stimuli. The primary purpose of this study was to use functional near-infrared spectroscopy (fNIRS) to determine if individuals with VV have different cerebral activation during optic flow compared with control subjects.

Methods

Fifteen individuals (5 males and 10 females in each group) with VV seeking care for dizziness and 15 healthy controls (CON) stood in a virtual reality environment and viewed anterior-posterior optic flow. The support surface was either fixed or sway-referenced. Changes in cerebral activation were recorded using fNIRS during periods of optic flow relative to a stationary visual environment. Postural sway of the head and center of mass was recorded using an electromagnetic tracker.

Results

Compared with CON, the VV group displayed decreased activation in the bilateral middle frontal regions when viewing optic flow while standing on a fixed platform. Despite both groups having significantly increased activation in most regions while viewing optic flow on a sway-referenced surface, the VV group did not have as much of an increase in the right middle frontal region when viewing unpredictable optic flow in comparison with the CON group.

Discussion and conclusions

Individuals with VV produced a pattern of reduced middle frontal cerebral activation when viewing optic flow compared with CON. Decreased activation in the middle frontal regions of the cerebral cortex may represent an alteration in control over the normal reciprocal inhibitory visual-vestibular interaction in visually dependent individuals. Although preliminary, these findings add to a growing body of literature using functional brain imaging to explore changes in cerebral activation in individuals with complaints of dizziness, disorientation, and unsteadiness. Future studies in larger samples should explore if this decreased activation is modified following a rehabilitation regimen consisting of visual habituation exercises.

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Visual vertigo and healthy controls process optic flow information differently.

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Visual vertigo had reduced bilateral middle frontal activation on a fixed platform.

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Visual vertigo had reduced right middle frontal activation on a moving platform.

Spatial and temporal postural analysis in children born prematurely

The aim of this study was to compare postural stability in a group of preterm-born children aged 4-6 years old and in a group of age-matched full-term control children by exploring both spatial and temporal analysis of the Center of Pressure (CoP). Twenty-nine children born prematurely (mean age: 5.38±0.17) and twenty-nine age-matched full-term control children participated in this study. Postural control was tested on both a stable and an unstable platform (from Framiral^®) in three different visual conditions: eyes open fixating a target, eyes closed, and with vision perturbed by optokinetic stimulation. We observed a significant increase of both surface area and mean velocity of the CoP in pre-term children compared to full-term control children, particularly in an unstable postural condition. The spectral power indices increased significantly in pre-term children with respect to full-term control children, while the cancelling time was not different between the two groups of children tested. We suggested that poor postural stability observed in preterm children could be due to immaturity of the cortical processes (the occipital parietal prefrontal cortex) involved in motor control. Preterm children could have an inappropriate compensation of sensory inputs when they are tested in difficult postural and/or visual conditions.

Development of adaptive sensorimotor control in infant sitting posture

A reliable and adaptive relationship between action and perception is necessary for postural control. Our understanding of how this adaptive sensorimotor control develops during infancy is very limited. This study examines the dynamic visual-postural relationship during early development. Twenty healthy infants were divided into 4 developmental groups (each n=5): sitting onset, standing alone, walking onset, and 1-year post-walking. During the experiment, the infant sat independently in a virtual moving-room in which anterior-posterior oscillations of visual motion were presented using a sum-of-sines technique with five input frequencies (from 0.12 to 1.24 Hz). Infants were tested in five conditions that varied in the amplitude of visual motion (from 0 to 8.64 cm). Gain and phase responses of infants' postural sway were analyzed. Our results showed that infants, from a few months post-sitting to 1 year post-walking, were able to control their sitting posture in response to various frequency and amplitude properties of the visual motion. Infants showed an adult-like inverted-U pattern for the frequency response to visual inputs with the highest gain at 0.52 and 0.76 Hz. As the visual motion amplitude increased, the gain response decreased. For the phase response, an adult-like frequency-dependent pattern was observed in all amplitude conditions for the experienced walkers. Newly sitting infants, however, showed variable postural behavior and did not systemically respond to the visual stimulus. Our results suggest that visual-postural entrainment and sensory re-weighting are fundamental processes that are present after a few months post sitting. Sensorimotor refinement during early postural development may result from the interactions of improved self-motion control and enhanced perceptual abilities.

The influence of kayaking and rowing sports experience on postural response to optic flow

This study investigated the postural response of kayakers and rowers to imposed optic flow. The athletes, with experience in unstable water environments, should have a specific postural response to optic flow. 12 male participants with kayaking and rowing experience and 12 with no specific sports experience were asked to stand still with and without room motion. This study varied the amplitude and frequency of room motion and evaluated the trajectory of the center of pressure. The kayaking and rowing group were less influenced by imposed optic flow, and body sway was more closely synchronized to the oscillating room compared to the Non-athlete group. These results suggest that postural adaptation occurs in association with experience in kayaking and rowing.

Adaptive visual re-weighting in children's postural control

This study investigated how children's postural control adapts to changes in the visual environment and whether they use previous experience to adjust postural responses to following expositions. Four-, eight-, and twelve-year-old children (10 in each group) and 10 young adults stood upright inside of a moving room during eight trials each lasting one-minute. In the first trial, the room was stationary. In the following seven trials, the room oscillated at 0.2 Hz, amplitude of 0.5 cm, with the exception of the fifth trial, in which the room oscillated with amplitude of 3.2 cm. Body sway responses of young adults and older children down-weighted more to the increased visual stimulus amplitude when compared to younger children. In addition, four- and eight-year-old children quickly up-weighted body responses to visual stimulus in the subsequent two trials after the high amplitude trial. Sway variability decreased with age and was greatest during the high-amplitude trial. These results indicate that four year olds have already developed the adaptive capability to quickly down-weight visual influences. However, the increased gain values and residual variability observed for the younger children suggest that they have not fully calibrated their adaptive response to that of the young adults tested. Moreover, younger children do not carry over their previous experience from the sensorial environment to adapt to future changes.

Perception-action and adaptation in postural control of children and adolescents with cerebral palsy

The aim of this study was to examine the coupling between visual information and body sway and the adaptation in this coupling of individuals with cerebral palsy (CP). Fifteen children with and 15 without CP, 6-15 years old, were required to stand upright inside of a moving room. All children first performed two trials with no movement of the room and eyes open or closed, then four trials in which the room oscillated at 0.2 or 0.5 Hz (peak velocity of 0.6 cm/s), one trial in which the room oscillated at 0.2 Hz (peak velocity of 3.5 cm/s), and finally two other trials in which the room oscillated again at 0.2 Hz (peak velocity of 0.6 cm/s). Participants with CP coupled body sway to visual information provided by the moving room, comparable to the coupling of participants without CP. However, participants with CP exhibited larger body sway in maintaining upright position and more variable sway when body sway was induced by visual manipulation. They showed adaptive sensory motor coupling, e.g. down-weighting visual influence when a larger stimulus was provided, but not with the same magnitude as typically developing participants. This indicates that participants with CP have less capability of adaptation.

Postural responses to a moving room in children with and without developmental coordination disorder

Children (10 or 11 years old) with and without developmental coordination disorder (DCD) were exposed to imposed optic flow in a moving room. We manipulated the amplitude and frequency of oscillatory room motion, and we evaluated the coupling of standing body sway with room oscillations. The results revealed that standing sway of both children with and without DCD was influenced by room motion. However, children with DCD responded differently than children without DCD to specific combinations of room motion amplitude and frequency. We conclude that DCD can influence a child's use of imposed optic flow for postural control and that these effects are situation-specific rather than being systemic.

Postural control and automaticity in dyslexic children: the relationship between visual information and body sway

Difficulty with literacy acquisition is only one of the symptoms of developmental dyslexia. Dyslexic children also show poor motor coordination and postural control. Those problems could be associated with automaticity, i.e., difficulty in performing a task without dispending a fair amount of conscious efforts. If this is the case, dyslexic children would show difficulties in using "unperceived" sensory cues to control body sway. Therefore, the aim of the study was to examine postural control performance and the coupling between visual information and body sway in dyslexic children. Ten dyslexic children and 10 non-dyslexic children stood upright inside a moving room that remained stationary or oscillated back and forward at frequencies of 0.2 or 0.5 Hz. Body sway magnitude and the relationship between the room's movement and body sway were examined. The results indicated that dyslexic children oscillated more than non-dyslexic children in both stationary and oscillating conditions. Visual manipulation induced body sway in all children but the coupling between visual information and body sway was weaker and more variable in dyslexic children. Based upon these results, we can suggest that dyslexic children use visual information to postural control with the same underlying processes as non-dyslexic children; however, dyslexic children show poorer performance and more variability while relating visual information and motor action even in a task that does not require an active cognitive and conscious motor involvement, which may be a further evidence of automaticity problem.

Age-related changes in postural control sensory reweighting

The aim of this study was to investigate the adaptive process in the coupling between visual information and body sway in children postural control. Twenty-seven children from 4-, 8- and 12-year-olds and ten adults stood upright inside of a moving room. In the first 2 min, the room was moved continuously at frequency of 0.2 Hz, velocity of 0.6 cm/s and amplitude of 0.5 cm. In the minute subsequent the room was moved with velocity of 3.5 and amplitude of 3.2 and in the last 2 min with velocity of 0.6 cm/s and amplitude of 0.5 cm. Gain, phase, SFSA and transient gain were used to examine the relationship between sensory information and body sway. The results showed that children and adults were capable to adapt to the changes of visual stimulus, downweighting the visual information influences when the room's amplitude/velocity increased. However, the young children did not show calibrated response to the 12-year-old children and adults level, being more influenced by the visual stimulus.

Development of multisensory reweighting for posture control in children

Reweighting to multisensory inputs adaptively contributes to stable and flexible upright stance control. However, few studies have examined how early a child develops multisensory reweighting ability, or how this ability develops through childhood. The purpose of the study was to characterize a developmental landscape of multisensory reweighting for upright postural control in children 4-10 years of age. Children were presented with simultaneous small-amplitude somatosensory and visual environmental movement at 0.28 and 0.2 Hz, respectively, within five conditions that independently varied the amplitude of the stimuli. The primary measure was body sway amplitude relative to each stimulus: touch gain and vision gain. We found that children can reweight to multisensory inputs from 4 years on. Specifically, intra-modal reweighting was exhibited by children as young as 4 years of age; however, inter-modal reweighting was only observed in the older children. The amount of reweighting increased with age indicating development of a better adaptive ability. Our results rigorously demonstrate the development of simultaneous reweighting to two sensory inputs for postural control in children. The present results provide further evidence that the development of multisensory reweighting contributes to more stable and flexible control of upright stance, which ultimately serves as the foundation for functional behaviors such as locomotion and reaching.

The influence of dynamic visual cues for postural control in children aged 7-12 years

Young children rely heavily on vision for postural control during the transition to walking. Although by 10 years of age, children have automatic postural responses similar to adults, it is not clear when the integration of sensory inputs becomes fully developed. The purpose of this study was to examine this transition in the sensory integration process in children aged 7-12 years. Healthy children and adults stood on a fixed or sway-referenced support surface while viewing full-field optic flow scenes that moved sinusoidally (0.1 and 0.25 Hz) in an anterior-posterior direction. Center of pressure was recorded, and measures of sway amplitude and phase were calculated at each stimulus frequency. Children and adults had significant postural responses during approximately two-thirds of the trials. In adults, there was a 90% decrease in sway on the fixed surface compared with the sway-referenced surface, but only a 50% decrease in children. The phase between the optic flow stimulus and postural response in children led that of adults by 52 degrees at 0.1 Hz and by 15 degrees at 0.25 Hz. Adults and children aged 7-12 years have similar ability to use dynamic visual cues for postural control. However, 7-12-year-old children do not utilize somatosensory cues to stabilize posture to the same extent as adults when visual and somatosensory cues are conflicting.

Postural control in children. Coupling to dynamic somatosensory information

The purpose of this investigation was to determine whether the coupling between dynamic somatosensory information and body sway is similar in children and adults. Thirty children (4-, 6-, and 8-year-olds) and 10 adults stood upright, with feet parallel, and lightly contacting the fingertip to a rigid metal plate that moved rhythmically at 0.2, 0.5, and 0.8 Hz. Light touch to the moving contact surface induced postural sway in all participants. The somatosensory stimulus produced a broadband frequency response in children, while the adult response was primarily at the driving frequency. Gain, as a function of frequency, was qualitatively the same in children and adults. Phase decreased less in 4-year-olds than other age groups, suggesting a weaker coupling to position information in the sensory stimulus. Postural sway variability was larger in children than adults. These findings suggest that, even as young as age 6, children show well-developed coupling to the sensory stimulus. However, unlike adults, this coupling is not well focused at the frequency specified by the somatosensory signal. Children may be unable to uncouple from sensory information that is less relevant to the task, resulting in a broadband response in their frequency spectrum. Moreover, higher sway variability may not result from the sensory feedback process, but rather from the children's underdeveloped ability to estimate an internal model of body orientation.

Brief report: postural reactivity to fast visual motion differentiates autistic from children with Asperger syndrome

The aim of the present study was to search for a sensorimotor marker (i.e., visuopostural tuning) that could be correlated with the severity of motor impairments in children with autistic spectrum disorders. Given that autistic children were previously reported to be posturally hyporeactive to visually perceived environmental motion in comparison with normal control children (Gepner et al., 1995), we sought to determine whether children with Asperger syndrome (AS) would share the same postural hyporeactivity to visual motion. Three autistic children with mild to severe motor impairments, three AS children with soft motor signs, and nine normal control children were tested for overall postural instability and postural reactivity to environmental motion. Results indicate, first, that overall postural instability is significantly reduced in autistic children compared with both AS and normal children. Second, although postural oscillations in the fore-aft axis become more attuned to the oscillation frequency of an immersive dynamic visual display as visual speed is increased, in both control and AS subjects, this is not the case in autistic children. Despite the small number of subjects tested in this study, our data confirm the existence of a visuopostural detuning in autistic children. Third, they argue for a correlation between visuopostural tuning and severity of motor signs in children with autistic spectrum disorders. Finally, they suggest a differentiation between children with autism and children with AS with regard to postural reactivity to fast visual motion. Neurophysiological implications of these results are discussed. In particular, a visuocerebellar pathway deficit hypothesis in autism is proposed.

The flip side of perception-action coupling: locomotor experience and the ontogeny of visual-postural coupling

The possible role of motor development on psychological function is once again a topic of great theoretical and practical importance. The revival of this issue has stemmed from a different approach to the topic, away from Gesell's interest in the long-term prediction of psychological functions from early motoric assessments, toward an attempt to understand how the acquisition of motor skills orchestrates psychological changes. This paper describes how the acquisition of one motor skill, prone locomotion, has been linked to developmental changes in an infant's ability to regulate posture based on information available in patterns of optic flow. It is argued that the onset of prone locomotion presses the infant to differentiate spatially delimited regions of optic flow to effectively and efficiently control the important subtasks nested within the larger task of locomotion, namely, steering, attending to the surface of support, and maintaining postural control. Following this argument, a research program is described that aims to determine if locomotor experience is causally linked to improvements in the ability to functionalize peripheral optic flow for postural control or whether locomotor experience is merely a maturational forecaster of such improvements. Finally, a hypothesis is put forward that links the emergence of wariness of heights to infants' ability to regulate posture on the basis of peripheral optic flow. The paper's overarching theoretical point is the principle of probabilistic epigenesis, which states that one developmental acquisition produces experiences that bring about a host of new developmental changes in the same and different domains.