Attending to the non-preferred hand improves bimanual coordination in children

Abstract

The effect of attentional focus in bimanual coordination was investigated from a developmental perspective by examining performance of right- and left-handed children, 5–8-years and 9–12-years old, on bimanual reciprocal tapping tasks. Attentional focus was either specified, by asking the children to attend to the preferred or to the non-preferred hand, or unspecified for the execution of the tasks. When attention was oriented to the non-preferred hand we found a reduced movement time and a lower frequency of errors. Performance differences for handedness and age-groups were observed when the children were oriented to attend to the preferred hand or when there was no instruction regarding attention. These differences in performance were eliminated when attention was oriented to the non-preferred hand.

Introduction

Human laterality is characterized by a well-defined lateral preference for, and a higher performance with, the preferred hand. Investigating this theme from a developmental perspective, Gesell and Ames (1947) showed that the first year of life is characterized by changes in manual preference, but for ages between 4 and 10, children were found to stabilize manual preference by consistently using a single hand for unimanual tasks. Further evidence that hand preference becomes more defined as children get older has been presented by Gudmundsson (1993), with results showing a higher proportion of consistent right-handers at the age of 6–9 years as compared with 3–5-years old. This early lateral preference for the right hand has been shown to be paralleled by performance asymmetries in tasks requiring manual aiming at a spatial target such as fast movement from one board to another (Annett, 1970). In his study, Annett (1970) showed a stable index of lateral asymmetry in children from the age of 3.5 years. An improved performance in right-handers for the right hand has also been found in reciprocal tapping tasks, in which 6- and 9-year old children tapped alternately two targets as fast as possible with either hand (Fagard, 1987). The results demonstrated that movement time was significantly shorter for the right hand across all ages.

The results referred to above indicate early in motor development a consistent advantage for the right hand in unimanual aiming tasks. An interesting question is whether this lateral asymmetry in children is expressed in the control of bimanual actions. Previous studies in bimanual aiming tasks by adults have shown that lateral asymmetries observed in unimanual performance can be suppressed when the hands are coordinated in simultaneous movements (Kelso et al., 1983, Kelso et al., 1979). More specifically, Kelso and colleagues showed that in bimanual tasks, when the right- and left-hand movements are aimed simultaneously to targets of equal size, there is a dramatic reduction in the velocity of the dominant hand, leading to similar movement times between hands. This apparent annihilation of performance asymmetry has been interpreted as a consequence of a control based on a functional unit, which couples the action of both hands. Additional investigation, however, has shown that, despite a clear reduction of performance asymmetry in such a discrete task, there is a small but steady advantage for the dominant hand that is manifest through shorter movement times as compared with the non-dominant hand (Fowler, Duck, Mosher, & Mathieson, 1991).

A similar pattern of results has also been found in continuous movements. A small but significant manual asymmetry was observed by Swinnen, Jardin, and Meulenbroek (1996) in a task requiring the production of continuous in-phase bimanual circle drawing in a horizontal plane. In their study, right- and left-handed participants were exposed to different visual conditions while performing the task: free vision, visual monitoring of the dominant or the non-dominant hand, and no vision. The results showed that during the circle drawing task the dominant hand led the non-dominant hand. The phase lag between the moving hands was modulated by handedness in that the phase lag was longer in right-handers than in left-handers. This increased phase lag in right-handers has been conceived to be due to a more lateralized bimanual control in these individuals than in left-handers. The leading role played by the dominant hand in bimanual tasks has also been observed in other studies (Amazeen et al., 1997, Stucchi and Viviani, 1993, Treffner and Turvey, 1995), and, it may be related to the capacity of the contralateral cerebral hemisphere to control fast movements in conditions of either unimanual (Carson et al., 1992, Elliott et al., 1993, Roy et al., 1994) or bimanual (Peters, 1994, Peters and Servos, 1989) motor actions.

Furthermore, the results by Swinnen et al. (1996) showed that manual asymmetry can be increased or attenuated by the direction of visual monitoring. In particular, phase lag was largest when vision was directed to the dominant hand, and smallest when vision was directed to the non-dominant hand. Visual information represents an important source of natural attraction for the focus of attention (Klein & Posner, 1974). In the case of bimanual actions, such visual information appears to modulate the performance by increasing or reducing lateral asymmetries (cf. Amazeen et al., 1997, Pellechia and Turvey, 2001, Treffner and Turvey, 1995). For example, when attention is oriented to the non-dominant hand, it attenuates the intrinsic disadvantage of the motor system, reducing the phase lag.

Robertson (2001), in a developmental study, investigated the predictions from the dynamical system theory related to the intrinsic dynamics and variability of bimanual coordination. Four-, 6-, 7-, 8- and 10-year-old children and adults performed unimanual dominant, unimanual non-dominant, and bimanual continuous circle drawing at the participant’s preferred rate, size, and mode of coordination. The 4-, 6-, and 7-year olds spent more time in less stable patterns, showed higher standard deviation of relative phase and produced more transitions between modes of coordination than the older age groups. Of special interest for the present study was the analysis of Robertson’s videotaped sessions that allowed the author to infer the notion of variables of attention related to age.

Little is known about the influence of directing attention in bimanual coordination in left- and right-handed children. However, this information could be helpful for those teaching motor skills. The influence of the focus of attention on bimanual coordination was investigated in the present study in right- and left-handed children. To examine this issue, we used a similar strategy to that employed by Swinnen et al. (1996), by asking the children either to focus his/her visual attention to the movements performed by one of the limbs, or choose the visual focus during the execution of continuous bimanual tapping tasks. Considering that handedness is in a process of consolidation during the first decade of life (Gesell and Ames, 1947, Gudmundsson, 1993), one additional question was whether bimanual coordination in children is affected by manual dominance in the same way in adults. We also examined a possible interaction of the focus of attention and handedness with spatial accuracy requirements for the task. If attention modulates lateral asymmetry in bimanual coordination, then we should expect higher speeds, lower error rates, and closer coupling of the hands for both right- and left-handed children, as a function of direction of attention. Modulation by attention may be only applicable for conditions requiring visual information as in tasks presenting a narrower spatial target. The effects of attention and handedness in children’s bimanual performances were assessed both temporally (movement time, relative phase) and spatially (frequency of errors). It is our expectation that the results from the present study will clarify the role of directing attention to one of the hands, and that, in the long run, this information will help teachers decide how to use the learner’s visual attention to improve the acquisition of bimanual skills.