CHAPTER I
THE NATURE AND SCOPE OF THE PROBLEM
Introduction
As far as human walking is concerned, it has been best described as the progression of the body’s center of mass along a pathway by moving the two legs alternatively. It is generally acknowledged that the development of walking skill in human beings is completed by the age of five (Sutherland, 1980). Locomotion is influenced by interactions between neuromuscular activity as well as musculoskeletal alignment (Perry & Burnfield, 2010). In addition, there are several other factors that can affect the coordination pattern of walking. These include sensory information from somatosensory, visual and vestibular systems and joint range of motion (also called ROM), and strength (Ricotti, 2011). Under normal conditions, vision is dominant in the control of gait, posture and goal-directed movements (Hallemans et al., 2009).
It has been approved that that visual deprivation has a significant effect on the gait pattern of developing children growing typically (Hallemans, 2009). These differences between eye-open and eye-closed indicate a more cautious walking strategy in the absence of vision (Hallemans, 2009). Moreover, visual perturbation including blurring and perturbed or occluding vision result in different adaptations in the gait pattern such as a decrease in walking speed, a decrease in step length and an increase in foot placement error, as well as deviations from a straight path (Hallemans, 2010).
In children, the developmental disabilities, autism, congenital anomalies, and degenerative changes can disturb the balance between interacting factors. These conditions can ultimately result in diminished gait efficiency (Perry & Burnfield, 2010). Autism is a neuro-developmental disorder that is apparent in a child before three years of age. According to the 2013 Diagnostic and Statistical Manual of Mental Disorders (DSM-5), all children with autism, Asperger’s syndrome, or other pervasive developmental disorders received one umbrella diagnosis of autism spectrum disorder (ASD).
Gross motor and gait abnormalities such as clumsiness have also been commonly reported in individuals with autism. In particular, these abnormalities are more noticeable in “high functioning,” that is, less cognitively impaired individuals due to cerebellum and basal ganglia affectation (Rinehart et al., 2006; Molloy, 2003). It was proposed that the gait problem in children with autism is not entirely social in nature and that a visual perceptual impairment might also contribute (Behrmann et al., 2006). Visual perceptual disorders such as visual spatial disorder and depth perception may affect utilization of visual sensory input for motor planning and control in children with autism (Glazebrook et al. 2009). For that reason, these children cannot locate things using their visual system. However, they mostly use their motor system to locate and get to the required thing/object.
Motivated by the dynamic systems theory approach (Haken et al., 1985; Kelso, 1995), three levels of behavioral control were outlined. These included the goal level (control of the entire movement trajectory), the timing level (control of relative timing between segment movements), and the load level (control against the external perturbation). On the other hand, studies that were conducted for examining walking primarily focused on the behavioral control at the goal and the load level for children developing typically (Hallemans, Ortibus, Meire, & Aerts, 2010; Hallemans et al., 2009). In contrast, children with autism were assessed considering the goal level (Kindregan, Gallagher, & Gormley, 2015). To put it more simply, this study attempted to examine children with autism in response to the visual perturbation at the load level during walking compared with the typically-developing children.
In order to understand the gait pattern deviation in autistic children, it is excessively significant to understand the influence of the visual perturbation on the gait pattern and gait pattern stability in these children. This study will give the physical therapists the opportunity to provide maximum early interventions. Consequently, it will also assist the concerned families in decreasing the cost of services required to treat the children with autism. Therefore, the purpose of this study is to examine the influence of the visual perturbation on gait among typically-developing children and children with autism.
STATEMENT OF THE PROBLEM
The purpose of the study is to examine the influence of visual perturbation on gait among typically-developing children and children with autism.
SUBPROBLEMS
The following subordinate problems will be inherent in the main problem of this study:
without visual perturbation (eyes open)
i) with visual perturbation (closed eyes), or
ii) virtual reality in children with autism compared with the typically-developing children aged 6-10 years
without visual perturbation (eyes open)
i) with visual perturbation (closed eyes), or
ii) virtual reality in children with autism compared with the typically-developing children aged 6-10 years
Dependent Variables / Independent Variables
The following specific and technical terms are defined for purposes of this study:
Visual perturbation: independent variable; refers to the disruption of the normal visual- motor interaction (Hansen et al., 2006). In this study, walking with visual perturbations is defined as walking with eyes closed, or walking while being exposed to virtual environment.
Gait Pattern: dependent variable; refers to changing the alignment between the body and supporting foot during stance and selective advancement of the limb segments in swing (describing the spatial and temporal pattern of gait) (Perry & Burnfield, 2010). In this study, gait pattern will be measured by the spatial and temporal parameters of the gait.
Gait pattern stability: dependent variable; refers to consistency of the gait pattern (Magill, 2010). In this study, gait pattern stability will be measured by standard deviation of overall walking duration, speed of walking, and spatial characteristics of walking.
Self-selected speed: refers to the speed at which an individual chooses to walk voluntarily (Perry & Burnfield, 2010). In this study, self-selected speed was determined by asking the subjects to walk at their most comfortable speed.
Research Hypotheses
Significant difference will be found between gait patterns in children with autism compared to the typically-developing children. Furthermore, this difference will be increased when walking with visual perturbation; closed more than VR than walking without visual perturbation.
Gait pattern stability will decrease when children with autism walk with visual perturbation, closed eye more than VR, as compared to walking without visual perturbation. Furthermore, gait pattern will be less stable in children with autism compared with typically-developing children.
Rationale for Hypothesis I
The first hypothesis states that significant difference will be found between gait patterns in children with autism compared by the typically-developing children. Furthermore, this difference will be increased when walking with visual perturbation, closed more than VR, than walking without visual perturbation. As the dynamic systems theory suggests, coordinated movement is determined by the interaction of the movement segment with several constraints, such as visual perturbation in this study. On the basis of this theory, the individual adjusts the movement’s timing (temporal pattern) or the movement’s amplitude (spatial pattern) to maintain the coordinated pattern of walking when a perturbation is applied to the body (Magil & Anderson, 2014).
According to the feedback control theory, adjustments to the movement trajectory are made based on visual and pro-prioceptive information that are later compared to an internal representation of the movement (Davidson and Wolpert, 2005). In the natural environment, both visual and pro-prioceptive information are available to individuals for the motor control of their aiming movements. Children with autism rely mainly on visual input for balance (Molloy et al., 2003). Thus, if there is disruption in the visual inputs or processing by the central nervous system (CNS), the feedback control will be disturbed consequently influencing the movement pattern. Based on the two previous concepts, we expect that the children with autism will have significant differences in their gait patterns as compared to the typically-developing children. In addition, this difference will be increased when observing walking with visual perturbation, closed more than VR, than walking without visual perturbation.
Rationale for Hypothesis II
The second hypothesis states that gait pattern stability will decrease when children with autism walk with visual perturbation, closed eye more than VR, as compared to walking without visual perturbation. Furthermore, gait pattern will be less stable in children with autism compared with typically-developing children. Control parameters, the visual perturbation in this study, are variables that influence the movement pattern stability. According to the dynamic systems theory, the variations in the control parameters cause variations in the stability of the movement patterns contributing to an individual’s behavior. Moreover, the stability of the movement pattern decreases when the intensity of the control parameter is increased. Considering this concept, we expect children with autism to demonstrate less stability than typically-developing children and with even less stability with visual perturbation, closed eyes more than VR.
CHAPTER II
THE RELATED LITERATURE
Introduction
The literature review consists of two sections. The first section presents a review concerning normal walking in children and their motor control and the role of the vision in walking. The second section talks about children with autism, different visual problems, and various gait abnormalities associated with autistic children.
Normal Walking in Children
Locomotion is an extremely complex attempt involving interaction of skeletal alignment, joint range of motion, neuromuscular activity, and the rules governing bodies in motion. A number of researchers have examined the development of gait in normal children. One study that involved 186 children (aged 01-07 years) identified several important determinants of mature gait: cadence, velocity, duration of the single support phase, and step length. It was concluded that gait was largely mature by the age of 3 years (Sutherland, Olshen, Cooper, & Woo, 1980). In another larger study involving 309 children, it was concludes that the interrelationships between time and distance parameters were fixed by the age of 4 (Hillman, Stansfield, Richardson, & Robb, 2009).The majority of the research on human walking has focused on the movement of the lower extremities which is simplified into the foot step parameters. These include spatial parameters; stride and step lengths, and temporal parameters; cycle time, stance and swing duration (Perry & Burnfield, 2010).
Motor Control of Normal Gait
The motor control of gait consists of higher level central nervous system (CNS) involvement along with musculoskeletal dynamics and environmental interaction. Gait control also depends on both pro-prioception and vision as the source of sensory information for the augmentation and modification of movement commands generated by CNS (Molloy et al, 2003). Dynamic Systems Theory is a renowned theoretical approach for understanding the formation of movement patterns. Bernstein states that “coordination of movement is the process of mastering the redundant degree of freedom of the moving organism” (enter the year here). Although Bernstein did not provide a definite answer to the problem of the degree of freedom, he realized that the coordinated movement is determined by the interaction among several constraints. These constraints can come from the environment, the task, and the body. Therefore, an individual adjusts the temporal pattern or the spatial pattern to maintain the coordinated movement of the walking when a perturbation is applied to the body (Magil & Anderson, 2014). Most of the research studies investigated the spatial and temporal parameters of the gait as a measurement of the gait pattern control in typically-developing children (Hillman et al., 2009; Sutherland et al., 1980).
Role of Visual Inputs in Gait Control
Vision is more than a source of feedback. It also influences movement characteristics before the initiation of any action. The visual system provides information about the environment from a distance and plays an important role during locomotion in the maintenance of stability and motor planning. Visual perception of the environment during locomotion allows orientation towards a goal, adjusting the direction, avoiding collisions with objects, avoiding obstacles and accommodating different surfaces. Visual perception of self-motion, lower-extremity position and movement is also important in order to adjust either foot clearance or foot placement and to regulate walking speed (Hollands & Marple-Horvat, 1996).
Many researchers investigated the role of vision during gait by manipulating the amount of visual information that reaches the eye such as blurring, perturbed (e.g. by optic flow) or occluding vision. The results demonstrated that vision is important for gait control even in an organized environment. The differences between the full vision and no-vision conditions may reflect a more cautious walking strategy and different adaptations in the gait pattern such as a decrease in walking speed, a decrease in step/ stride length, lower cadence (Hallemans et al., 2010; Hallemans et al., 2009).
Children with Autism
Autism is a neuro-developmental disorder affects boys four times more than the girls (Fombonne, 1999). The diagnosis of autism requires that specific clinical criteria be met in the areas of communication, reciprocal social interaction, and stereotypic behavior (American Psychiatric Association, 2000). Recent epidemiological studies in the United States provide prevalence estimates in the 60-70/10,000 range, making autism as one of the most frequently observed childhood neuro-developmental disorder (Fombonne, 2009). There is no biological marker for children with autism. However, there is strong evidence of a genetic susceptibility to the disorder (Bailey et al., 1995; Lamb, Moore, Bailey, & Monaco, 2000). Yet, no definitive etiology has been determined. Recent brain imaging and neuro-physiological studies implicate both the basal-ganglia frontostriatal and cerebellar regions in autism.
Children with autism are associated with greater clumsiness, motor coordination abnormalities, postural instability, and poor performance on standardized tests of motor functioning (Molloy et al., 2003). Also, children with autism are associated with deficits in smooth pursuit and saccadic eye movements (Kindregan et al., 2015) and visual perceptual defect (Behrmann et al., 2006). Therefore, children with autism are regarded as a major population to be studied by the physical therapy researchers.
Visual Problems Associated with Children with Autism
There are different visual problems associated with autism. Children with autism are associated with visual perception of motion such as visual spatial and depth disorder. This was investigated in a study of children’s postural reactions to optic flow that may affect the utilization of visual sensory input for motor planning and control (Gepner, Mestre, Masson, & de Schonen, 1995). Some studies investigated the motion coherence threshold in children with autism and concluded that children with autism have higher coherence thresholds than the typically-developing children. It also suggested postural hypo-reactivity for visual moving objects (Gepner and Mestre, 2002a; Gepner et al., 1995). Based on the previous literature, lack of accuracy of the visual inputs may affect the motor control and motor planning of movement.
Gait Abnormalities Associated with Children with Autism
Gait abnormality can be simply defined as a deviation from normal walking pattern. Many studies have subsequently examined motor coordination in children with autism and concluded that children diagnosed with autism have less coordinated movement patterns than the typically-developing children. This may, therefore, suggest that gait disturbances, such as clumsy gait, may be common among children with autism. Children with autism have been found to demonstrate other numerous gait stereotypes such as pacing, jumping, hopping, skipping, and spinning. It has been suggested that these may also be considered restrictive and repetitive behavior (Kindregan et al., 2015). The temporospatial parameters that have been examined in children are stride length, step length, step width, cadence (steps per minute), velocity, stance time, and double support. It was reported in a systematic review that children with autism have increased stride/step length, increased step width, decreased cadence in one study but increased in other, and increased stance time as compared to the typically-developing children. (Kindregan et al., 2015)
In summary, the literature review revealed that children with autism have different gait patterns than the typically-developing children. It was also observed that there is an increased variability of gait parameters in children with autism than the typically-developing children. Moreover, children with typical development have different gait patterns when they walk with and without visual perturbation. Nevertheless, no study investigated the effect of the visual perturbation on the gait pattern in children with autism. Therefore, the purpose of this experimental study will be to examine the influence of the visual perturbation on gait among typically-developing children and children with autism.
