Effect of postural instability on drawing errors in children: A synchronized kinematic analysis of hand drawing and body motion
Introduction
Fine motor skills, such as drawing a line through a narrow path, require not only manual dexterity, but also demand sustained attention and stable posture. A drawer needs to continuously focus on the task at hand, while filtering out irrelevant information from within themselves and from the external environment. Small-muscle and hand–eye coordination must be supported by large muscles that maintain and adjust posture and balance. Given the crucial roles that attention and posture play, how can we determine the extent to which attention and posture contribute to the execution of fine motor skills? Do those who have difficulties in fine motor skills have problems in attention, or postural control?
The relationship between attention and postural control has been studied in children with attention deficit hyperactivity disorder (ADHD). These children are typically restless and fidget while engaged in lengthy choice reaction time tasks like the continuous performance test (CPT). Tripp and Luk (1997) counted the number of movements at the wrist and the ankle using actometers which recorded swings of pendulums as the respective body parts moved. The children who pervasively exhibited the symptoms of ADHD in clinic, school, and home moved their wrists and ankles more than children with situational ADHD (exhibited only at school or home), and the control children without ADHD. Teicher, Ito, Glod, and Barber (1996) measured body motion more objectively with 3-D kinematic analysis, and found that a group of boys with ADHD moved their head, shoulder, and wrist more, and covered greater areas with linear and less complex patterns than a control group of boys without ADHD. Both studies confirmed poor sustained attention in children with ADHD as reflected in high error rates on the CPT, and hyperactivity based on objectively measured body movements.
The CPT demanded attention to stimulus identification and response selection. On the other hand the attention and motor skills required for the motor component of the response to press a computer key were minimal. While engaged in the CPT, only a finger is used to press the computer key, and therefore it is reasonable to interpret the movements of body parts distant from the hand (e.g., the ankles’ motion) as “fidgeting” because the movements of the body parts do not interfere with the manual responses. However, the hands are mechanically linked with and perturbed by the movements of the wrists and shoulders. Further, the head movements not only affect the vestibular, proprioceptive, and visual functions (Crowell, Banks, Shenoy, & Andersen, 1998), but are also functionally coupled with the eye and the hand movements (Pelz et al., 2001, Werner et al., 2000). While perturbation in the coordinative structure, or synergy of the head, eye, and hand may not affect the execution of such a simple ballistic motor task as pressing a key with a finger, it could nevertheless impact on the performance of more complex and enduring fine motor tasks. How do attention, posture, and motor skill interact given that both postural stability and attention are requisite for a fine motor skill?
The relationships between postural stability and fine motor skills have been investigated by examining the effect of postural support on fine motor performance, the effect of postural tremor on the steadiness of the hand, and the effect of postural muscle activity on arm movement. Infants improved their reaching behaviors when their posture was stabilized either with a seating device (Hopkins & Rönnqvist, 2004) or with therapeutic seating (Redstone & West, 2004). Johnson and Williams (1988) found that increased postural support improved pegboard performance in children with delayed gross motor development, but did not affect the performance of typically developing children. The researchers emphasized the need for postural support when children with gross motor delay perform fine motor skills. Birnbaum, Majnemer, Shevell, Limperopoulos, and Wood-Dauphinee (1999) demonstrated that children with postural tremor had difficulties holding their upper extremity steady while holding a stylus still with the end point placed in designated openings. These results suggest that postural instability is related to poor fine motor performance, such as handwriting. Finally, Johnston, Burns, Brauer, and Richardson (2002) conducted an EMG investigation of postural muscle activity before the arm starts reaching to a target, and revealed that the trunk of children with developmental coordination disorder (DCD) was not as well stabilized as children without DCD. All these studies provided evidence that alteration in posture stability affects fine motor performance, and that gross motor problems of posture instability is mechanically linked with the execution of fine motor skills.
Miyahara, Piek, and Barrett (2006) investigated the direct effect of obligatory attention in a fine motor skill, using a dual-task combined with a resistance-to-distraction paradigm. For the primary fine motor task they examined a standardized visual-motor control subtest (Bruininks, 1978) in which children with ADHD and without ADHD drew a line along a designated path. They performed this concurrently with a secondary task or distraction. No significant group difference was found, and we concluded that the errors in the primary fine motor task were caused by poor manual dexterity, and not by a lack of attention.
In this study we consider the analysis of 3-D kinematic data from the head, shoulder, and the elbow that were not reported by Miyahara et al. (2006). We use a method for data collection similar to that employed by Teicher et al. (1996). The present study examines specifically whether movements of the head, shoulder, and elbow, which are mechanically linked with the hand, occur prior to the performer committing an error in accuracy drawing. We intentionally avoid the notion of closed kinematic chain, or a linkage of rigid bodies, because the elbow or the forearm or the hand was often used as the anchor which could serve as error compensation. It is also difficult to determine if the end segment of the fingers and the thumb holding the pen on the tablet should be considered free in space or not. Accordingly, we refer instead to a postural instability which might be somehow, if not directly, linked as a cause of drawing errors. This postural instability may result from movement of the head, shoulder, or elbow. We examine drawing errors and postural stability in groups of children assessed for being accurate drawers and inaccurate drawers. Symptoms of inattention and hyperactivity/impulsivity were also assessed to rule out the possibility that the errors were a result of these behavioral problems, as fine motor problems are often linked to attention deficit hyperactivity disorder (e.g., Pitcher, Piek, & Hay, 2003).
Section snippets
Participants
A total of 24 children (9 girls, 15 boys), whose ages ranged from 5 to 11 years (M = 7.79, SD = 2.11), were recruited from schools, support groups, and clinics in Dunedin, New Zealand for a study on “children’s attention and coordination”. Except for the age range of primary school children, no inclusion and exclusion criteria, such as the presence or absence of difficulties in attention and coordination, were specified in the information sheet for the study. In fact, we had expected the
Bivariate correlations
Coincident rates were not significantly correlated with the variables of age, inattention, and hyperactivitiy/impulsivity at the head, shoulder, or elbow (see Table 2). None of these variables were used as covariates in subsequent analyses.
Postural instability of accurate and inaccurate drawers
We first examined coincidence rates of the three body parts between accurate drawers (AD) and inaccurate drawers (ID). In the ID group all participants produced coincidental movements for all three body parts. For the AD group all participants but three
Discussion
The present study revealed that the inaccurate drawers (ID) produced more movements in body parts adjacent to the drawing hand immediately prior to the commission of a drawing error compared to accurate drawers (AD). The result that the proximal body parts of the head and shoulder committed more coincident errors than the elbow, suggests that postural instability is important in fine motor control.
The increase in coincidence rates could not be attributed to inattention or
Acknowledgments
We wish to thank the participants, their parents, the schools and support groups for their participation in this research. Also thanks to Gavin Kennedy, Nigel Barrett, and Ian Case for their technical support, and Jenny Clarkson and Annelies Inghelbrecht for assisting data collection.
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