Mindful or mindless stepping? Does an external attentional focus improve dual-tasking after stroke?

Many stroke patients have difficulty with performing multiple tasks at the same time, like walking and talking. This negatively affects their mobility and fall risk. One way to target this problem is to enhance patients’ automaticity of movement, such that more attention is available for secondary task performance. But how can they achieve this? According to the “Constrained Action Hypothesis”, the answer is simple: instruct patients to direct attention externally on the movement goal, rather than internally on movement execution itself. In a previous study, we found that leg-stepping performance in healthy adults was unaffected by the imposition of a dual-task when they focused externally (on where to place their feet), but deteriorated when they focused internally (on flexing/extending their leg). The current study aimed to replicate these findings in patients with stroke.

Thirty-nine chronic hemiparetic stroke patients (M_age=62.6 years) performed a seated stepping task (Figure 1). Both legs were tested separately. Stepping speed was measured with accelerometers. In dual-task conditions, patients were tested on two different dual-tasks: a reaction time task and an executive function task. Using a counterbalanced, cross-over design, single- and dual-task performance was assessed under both external focus and internal focus conditions (Figure 1). Prior to the experiment, patients completed motor and cognitive tests, and a questionnaire regarding the degree to which they preferred internal or external focus in daily life. Results showed that single-task stepping speed in stroke patients was similar in both focus conditions (p=.34). Planned follow-up analysis revealed that patients performed best with the focus they preferred to use in daily life (p=.01). Regarding dual-task performance, patients performed better when they focused internally (p=.06; Figure 1). Also, their attentional capacity was more predictive of their dual-task performance in external compared to internal focus conditions (p=.05).

Different from healthy adults, external focus instructions did not improve single- or dual-task performance post-stroke. In fact, dual-task performance seemed better with an internal focus. One explanation for these findings is that the overall strong internal focus preference in our sample made switching to a relatively unfamiliar external focus so attention-demanding that it affected automaticity. This would also explain why attentional capacity was most important for dual-task performance in external focus conditions. In conclusion, our results implicate that stroke patients do not necessarily benefit from an external focus. Further research should explore how attentional focus influences dual-task performance post-stroke, specifically taking into account patients’ individual focus preferences.

Figure 1. Leg-stepping task (A, left) and dual-task results (B, right). The leg-stepping task was performed both in external and internal focus conditions. In external focus condition (A, lower panel) patients were instructed to focus on placing their foot in front of/behind a line that was taped on the floor. In the internal focus condition (A, lower panel) patients were instructed to focus on flexing and extending their leg. Dual-task performance (B, right) is expressed in dual-task costs (DTCs; ST_performance – DT_performance / ST_performance *100%). DTCs were calculated separately for the leg-stepping and cognitive tasks. Lower DTCs reflect better dual-task performance.

Publication

Kal EC, Van der Kamp J, Houdijk H, Van Bennekom C, Scherder EJA. (2016) Stay focused! The effects of internal and external focus of attention on movement automaticity in patients with stroke. PLoS One 10(8): e0136917. doi:10.1371/journal.pone.0136917 http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0136917

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