How Do I Fit through That Gap? Navigation through Apertures in Adults with and without Developmental Coordination Disorder

During everyday life we move around busy environments and encounter a range of obstacles, such as a narrow aperture forcing us to rotate our shoulders in order to pass through. In typically developing individuals the decision to rotate the shoulders is body scaled and this movement adaptation is temporally and spatially tailored to the size of the aperture. This is done effortlessly although it actually involves many complex skills. For individuals with Developmental Coordination Disorder (DCD) moving in a busy environment and negotiating obstacles presents a real challenge which can negatively impact on safety and participation in motor activities in everyday life. However, we have a limited understanding of the nature of the difficulties encountered. Therefore, this current study considered how adults with DCD make action judgements and movement adaptations while navigating apertures. Fifteen adults with DCD and 15 typically developing (TD) controls passed through a series of aperture sizes which were scaled to body size (0.9-2.1 times shoulder width). Spatial and temporal characteristics of movement were collected over the approach phase and while crossing the aperture. The decision to rotate the shoulders was not scaled in the same way for the two groups, with the adults with DCD showing a greater propensity to turn for larger apertures compared to the TD adults when body size alone was accounted for. However, when accounting for degree of lateral trunk movement and variability on the approach, we no longer saw differences between the two groups. In terms of the movement adaptations, the adults with DCD approached an aperture differently when a shoulder rotation was required and then adapted their movement sooner compared to their typical peers. These results point towards an adaptive strategy in adults with DCD which allows them to account for their movement difficulties and avoid collision

When an object appears unexpectedly: object circumvention in adults

Obstacles often appear unexpectedly in our pathway and these require us to make immediate adjustments. Despite how regularly we encounter such situations only few studies have considered how we adjust to unexpected obstacles in the pathway which require us to walk around them. The current study considered how adults adjust to the possibility of an obstacle appearing and then also how foot placement is adjusted to circumvent an obstacle. Fifteen healthy adults walked down an 11m walkway, initially they were told this was a clear pathway and nothing in the environment would change (no gate), they then performed a series of trials in which a gate may (gate close) or may not (gate open) partially obstruct their pathway. We found that medio-lateral trunk velocity and acceleration was significantly increased when there was the possibility of an obstacle but before the obstacle appeared. This demonstrates an adaptive walking strategy which seems to enable healthy young adults to successfully circumvent obstacles. We also categorised foot placement adjustments and found that adults favoured making shorter and wider steps away from the obstacle. We suggest this combination of adjustments allows participants to maintain stability whilst successfully circumventing the obstacle

Tailoring reach-to-grasp to intended action: the role of motor practice

Motor learning results from repeated exposure to the same movement and allows a mover to increase movement optimality. Typically, this has only been considered in single-step movements. In sequential movements, an initial reach movement is tailored to the demands of the onward movement. However, the exact role of motor practice in the tailoring to onward task demands is unknown. Eighteen adults performed blocks of 15 movements; each movement consisted of areach phase and an onward phase (the object was placed in a tight-fitting hole, placed in a loose-fitting hole or thrown). Simple practice effects were seen; for the reach phase, the amount of time spent decelerating decreased over trials, and for the onward phase, the accuracy of the place/throw movements increased over trials. Furthermore, approximately 30 % of variance in the practice effect of the onward phase could be explained by the practice effect in the reach phase. Therefore, we suggest that the changes in the reach phase are directly linked to the changes in the efficiencyof action and that this is necessary but not sufficient for explaining the calibration of the onward action

The use of prescanning in the parameterization of sequential pointing and reaching movements

The accuracy of reaching movements improves when active gaze can be used to fixate on targets. The advantage of free gaze has been attributed to the use of ocular proprioception or efference signals for online control. The time course of this process, however, is not established, and it is unclear how far in advance gaze can move and still be used to parameterize subsequent movements. In this experiment, the authors considered the advantage of prescanning targets for both pointing and reaching movements. The authors manipulated the visual information and examined the extent to which prescanning of targets could compensate for a reduction in online visual feedback. In comparison with a conventional reaching/pointing condition, the error in pointing was reduced, the eye-hand lead decreased, and both the hand-closure time and the size of the maximum grip aperture in reaching were modulated when prescanning was allowed. These results indicate that briefly prescanning multiple targets just prior to the movement allows the refinement of subsequent hand movements that yields an improvement in accuracy. This study therefore provides additional evidence that the coordinate information arising from efference or ocular-proprioceptive signals can, for a limited period, be buffered and later used to generate a sequence of movements

Influences of grasp selection in typically developing children

When reaching towards an object, adults favour grasps which, following the intended action, end in a comfortable position even when this requires them to start in an uncomfortable position (the end-state-comfort effect). However, this strategy is not consistently used by children who instead seem to favour a minimal pre-contact rotation of the hand, even when this results in an uncomfortable end position. In terms of multiple movements, the strategies used for grip selection are unclear; adults may still grasp for end-state-comfort given their propensity to plan to the end of a movement; however, children who are less able to concatenate movement may tend to start-state-comfort movements. The current study considered grip selection in children ranging from 4 to 12 years and in a group of adults. Participants were asked to rotate a disc so that an arrow pointed towards a specific target(s), the number of sequences in a movement was increased from one to three. Planning for end-state-comfort was seen in all participants and a clear developmental trajectory was identified whereby the relative comfort of an end position could be directly predicted by age in months. Adults and 10–12-year-olds favoured an end-state-comfort strategy whereas the younger children gave equal weighting to end-state-comfort, start-state-comfort and no initial rotation strategies. All groups were able to end a movement comfortably when it was composed of three steps; however, the proportion of movements relying on an end-state-comfort strategy decreased as sequence length increase whereas the proportion of start-state-comfort and no initial rotation strategies increased. The current data support the concept that a mechanism for planning grasps may be based on motor experience

Speech and oro-motor function in children with developmental coordination disorder: a pilot study

The protracted maturation and development of speech articulation underlies the complexity of the skill, and suggests it may be an area susceptible to a general deficit in motor control. Recent research suggests a high co-occurrence between Developmental Coordination Disorder (DCD) and disordered speech production. Despite this there has been no systematic investigation of speech motor control in children with DCD. We conducted a pilot study which looked at speech motor control in a group of children with DCD (N = 5) and a group typically developing (TD) children (N = 5). Movements of the upper and lower lip were recorded during non-verbal movements, single words, syllable sequences, and sentence repetition. In the baseline conditions (normal talking speed or an isolated utterance) children with DCD demonstrated a typical pattern of movement, albeit a slower and shorter movement. In contrast, when task complexity was increased the children with DCD showed an atypical pattern of movement. It was concluded that children with DCD demonstrate inferior motor control for complex speech gestures, suggesting that the motor deficit in DCD may indeed be a more generalized phenomenon affecting the speech motor system

The use of predictive information is impaired in the actions of children and young adults with developmental coordination disorder

The need for a movement response may often be preceded by some advance information regarding direction or extent. We examined the ability of individuals with Developmental Coordination Disorder (DCD) to organise a movement in response to advance information. Pre-cues were presented and varied in the extent to which they indicated the response target. Both eye movement latencies and hand movements were measured. In the absence of pre-cues, individuals with DCD were as fast in initial hand movements as the typically developing (TD) participants, but were less efficient at correcting initial directional errors. A major difference was seen in the degree to which each group could use advance pre-cue information. TD participants were able to use pre-cue information to refine their actions. For the individuals with DCD this was only effective if there was no ambiguity in the advance cue and they had particular difficulty in using predictive motion cues. There were no differences in the speed of gaze responses which excluded an explanation relating to the dynamic allocation of attention. Individuals with DCD continued to rely on the slower strategy of fixating the target prior to initiating a hand movement, rather than using advance information to set initial movement parameters

Locomotor adjustments when navigating through apertures

During everyday locomotion we encounter a range of obstacles which require specific motor responses, for example a narrow aperture forces us to rotate the shoulders to pass through. Research has demonstrated that the decision to rotate the shoulders is body scaled (Warren & Whang, 1987) and that the visuo-motor system generates a rotation proportional to aperture size (Higuchi, Cinelli, Greig, & Patla, 2006). The current study considered how shoulder angle and movement speed are tailored to aperture size in nine adults. Aperture sizes were classified into shoulder/aperture ratios (SA ratio), including two for which participants had to rotate (0.9/1.1) and two for which participants could pass freely (1.5/1.7). During the initial approach phase (first 3 s), shoulder rotation and movement speed were invariant across SA ratio. Later in the movement, angle of shoulder rotation and the magnitude and timing of the reduction in speed were proportional to SA ratio. The timing of the reduction in speed was progressively later in the movement as SA ratio increased, suggesting early adjustments of movement, such as the timing of the reduction in speed are tightly tuned to the ratio between aperture size and shoulder width, even when no later body adjustments are needed

Navigating through apertures: perceptual judgements and actions of children with Developmental Coordination Disorder

Passing through a narrow gap/aperture involves a perceptual judgement regarding the size of the gap and an action to pass through. Children with DCD are known to have difficulties with perceptual judgments in near space but whether this extends to far space is unknown. Furthermore, in a recent study it was found that adults with DCD do not scale movements when walking through an aperture in the same way as their peers. The current study, therefore, considered perceptual judgments and motor behaviour of children with DCD while looking at or walking through apertures. Twenty-nine children with DCD and 29 typically developing (TD) children took part. In Experiment 1, participants completed a perceptual task, where they made passability judgements. Children with DCD showed a significantly smaller critical ratio (aperture size at which a participant first rotates the shoulders to pass through) compared to their TD peers. In Experiment 2, participants completed an action task where they walked through the same apertures. Children with DCD showed a significantly larger critical ratio than TD peers when body size alone was accounted for. Taken together these results suggest that perception within a static context is different from that within a dynamic context for children with DCD. However, despite this difference we have demonstrated a clear relationship between perception and action in children with DCD

The role of movement variability and action experience in the perceptual judgement of passability

​Perception and action are tightly coupled and previous studies have demonstrated that action experience can improve perceptual judgement. We investigated whether this improvement in perceptual judgement could be attributed to knowledge regarding movement variability being gained during action experience. Fifteen adults made perceptual judgments regarding the passability of a series of aperture sizes. These judgements were made both before and after walking through the same set of apertures (action experience). When considering the group as a whole perceptual judgement did not change after action experience. However, when splitting the group into those with low and high pre-action perceptual judgements, only those with low perceptual judgements showed an improvement in perceptual judgement following action experience and this could in part be explained by movement variability during the approach. These data demonstrate that action informs perception and that this allows adults to account for movement variability when making perceptual judgements regarding action capabilities