Attentional focus of feedback for improving performance of reach-to-grasp after stroke: a randomised crossover study
Introduction
Feedback about motor performance, defined as ‘observable production of a motor action’ [1], calibrates a motor response to the aims of the task [2] and can increase the level or rate at which motor learning occurs. When provided verbally, it can be directed to focus attention either on the body movement [internal focus (IF); e.g. ‘next time, straighten your elbow more’] or on the effects of the movement on the environment [external focus (EF); e.g. ‘next time, move closer to the jar’] [3]. In healthy participants, information feedback which induces an EF of attention has consistently led to improved motor performance compared with information feedback which induces an IF of attention [4], [5]. Following stroke, the effect of EF feedback on motor performance vs IF feedback is not known [6], but EF instructions have resulted in shorter movement times and greater peak velocities during functional reaching tasks [7] and improvements in balance [8].
The ‘constrained action hypothesis’ [9], [10] has been suggested to explain the advantage of inducing an EF of attention. This states that directing attention to movement itself (IF) causes the person to consciously intervene in automatic control processes, thereby disrupting them. In contrast, focusing on the movement effect (EF) reduces a person's ability to actively intervene in their control processes and consequently enables faster, more efficient automatic movements.
Not all studies have supported the advantage of feedback with an EF. In healthy novice performers learning a new skill, a small number of studies have found a benefit from instructions inducing an IF [11], [12]. It is possible that stroke participants may respond differently to type of attentional focus according to level of arm impairment, where those with severe motor impairment may benefit less from feedback inducing an EF of attention.
The influence of available working memory may also influence the benefit conferred by different attentional foci. Adopting an EF has been associated with using less explicit processes and so requires less working memory capacity [13], [14]. The ‘conscious processing hypothesis’ [15] proposes that explicit knowledge about the movement impedes performance and places increased load on working memory. It has been suggested that more working memory is required when inducing an IF of attention, as information from both body and salient features in the environment need to be processed, whereas with EF, only information from the environment is used [14]. Therefore, the motor performance of participants with impaired working memory may improve with an EF of attention.
In summary, it is not clear whether the benefit of EF over IF in healthy participants extends to improving motor performance after stroke. It is also unknown whether the level of motor impairment and working memory capacity are influential factors. In this exploratory study, it was hypothesised that feedback inducing an EF would be more effective than feedback inducing an IF in improving motor performance of reach-to-grasp after stroke. The study did not aim to assess retention of changes in motor performance (motor learning). Measures indicating motor performance of reach-to-grasp (transport of the hand and opening and closing of the hand) and the amplitude of joint movements were used to describe motor performance in this study, since both of these aspects are important in the therapeutic context [16], [17]. Secondly, it was predicted that stroke participants with greater arm impairment would benefit less from receiving feedback inducing an EF compared than those with lesser arm impairment. Thirdly, it was predicted that stroke participants with impaired working memory would benefit more from receiving feedback inducing an EF compared with those with good working memory.
Section snippets
Design
A crossover trial was employed where stratified randomisation via a computer-generated randomised sequence was used to assign participants to one of two feedback order groups: IF followed by EF or EF followed by IF. All participants performed reaching movements under both feedback conditions with a rest between conditions.
Stratification was performed to balance groups on two variables: upper limb impairment (upper limb section of the Fugl-Meyer Assessment: greater arm impairment ≤44; lesser arm
Stroke participants
Baseline characteristics of the two groups were similar with respect to age, time since stroke, and Fugl-Meyer and 10-hole peg test scores (Table 1).
A significantly shorter movement duration (F1,40 = 7.927, P = 0.008) and significantly increased %TPD was found for Task B (F1,35 = 7.405, P = 0.01) using EF compared with IF feedback. For Task A, a significantly increased %TPV (F1,40 = 4.539, P = 0.039) was found using EF compared with IF feedback. Movement duration in Task B was nearly 0.5 seconds faster with
Discussion
The results provide some support for the hypothesis that feedback inducing an EF of attention is more effective than feedback inducing an IF of attention in improving motor performance of reach-to-grasp movements after stroke. First, feedback inducing an EF of attention produced a shorter movement duration in Task B. An increased movement duration has been negatively associated with performing activities of daily living [30], [31]. As reach-to-grasp was over 1 second slower (between 2 and 2.5
Conclusions
Feedback inducing an EF of attention may be of some benefit for improving motor performance of reaching in people with stroke in the short term. However, an order effect was present whereby performance was improved if EF feedback was preceded by IF feedback. Therefore, these results should be interpreted with caution. Further research using a randomised design is recommended to enable effects on motor learning to be assessed.
Ethical approval: Black Country Research Ethics Committee
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