The effects of internal versus external attentional focus on a simple leg movement task under single and dual-task conditions in acquired brain injury

Many patients with acquired brain injury (ABI) are limited in their ability to
perform multiple tasks simultaneously. These impairments in dual task
performance can have serious consequences for their daily functioning and
quality of life. Therefore, it is necessary to develop interventions aimed at
improving dual task performance.

In essence, the mechanism behind dual task performance is relatively simple.
Task execution places a certain demand on working memory capacity. When
simultaneous execution of a secondary task is required, and the additional
demand on working memory capacity exceeds its limits, performance on one (or
both) task(s) will deteriorate. Therefore, reducing the demand placed on
working memory capacity by the execution of the primary task will yield more
residual capacity for the execution of a secondary task. An intervention that
might be able to effectuate this is manipulating focus of attention. The
constrained action hypothesis predicts that focusing on the effects of movement
(i.e., an external focus) induces automatic control of movement, whereas
focusing on the execution of one's movements (i.e., an internal focus) results
in consciously controlled (hence not automatized) movements. In this way, an
external focus of attention is hypothesized to result in superior movement
execution than an internal focus of attention. Indeed, it has been demonstrated
that an external focus results in superior motor learning and performance in a
broad range of tasks in healthy adults. However, to date, the effects of focus
manipulation on motor performance and motor-cognitive dual task performance of
ABI patients is virtually unknown.

The primary aim is to investigate the effects of attentional focus manipulation
on the performance of a repetitive leg movement task under single and dual-task
conditions in ABI patients. Furthermore, it will be investigated to what extent
the effects of attentional focus are influenced by location of brain damage,
and time since injury.

The secondary aim is to investigate whether an external focus of attention
leads to more automatized movements compared to an internal focus of attention.

The tertiary aim is to investigate to what extent the effects of attentional
focus on performance are mediated by aspects of cognitive and motor
functioning.

The effects of internal and external focus of attention will be investigated in
a randomized combined cross-sectional (part A) and short longitudinal (part B)
study. In part A, a group of recent ABI patients, a chronic group of ABI
patients and a healthy control group will be compared (T=1). This procedure is
described below. In part B the recent ABI group and healthy control group will
be measured again, following the same procedure as on T1, 6 months after
completion of the first assessment (T=2).

Part A
Participants will perform a cyclic leg movement task for which they were
required to alternately flex and extend their leg on a comfortable pace for one
minute. Attentional focus will be instructed before the start of each trial via
standardized written instructions. In two-thirds of the trials participants
will perform the leg movement task concurrently with a cognitive task. Half of
these trials this will be a letter fluency task, for which participants are
required to name as many unique words as possible during one minute starting
with a specified letter. In the other half of the trials this will be an
auditory recognition task, in which participants are required to verbally
respond to an auditory target stimulus (by saying "yes") as fast as possible,
but ignore irrelevant stimuli.

Procedure:
All participants complete a neuropsychological assessment and the Reinvestment
Scale on day 1. For the patient groups motor functioning is assessed as well.

On the second measurement day baseline performance on the motor task, auditory
recognition task, and letter fluency task is assessed. To this end,
participants perform the leg movement task with no specific instructions
regarding attentional focus with both legs. Next, 6 trials are performed with
one leg, and after a short break of 10 minutes 6 trials are performed with the
other leg. Trials are separated by at least three minutes of rest, or more if
requested by the participant. All trials on this measurement day will be
performed with either an external or an internal focus of attention.

On the third measurement day, the same procedure is applied as on the second
measurement day with the other focus of attention.

It is counterbalanced whether participants start with an external or an
internal focus and whether they start with their dominant/less affected leg or
with their non-dominant/paretic leg.

The experimental intervention is the manipulation of attentional focus.
Participants will be instructed to focus on alternately placing their foot in
front of/behind a line on the ground (i.e., an external focus), or to focus on
alternately flexing and extending their leg (i.e., an internal focus).

The risks associated with participation in this study are negligible. The
experimental tasks resemble daily activities of low intensity with which the
participants have ample experience. Moreover, the resting periods between
trials are of considerable length to minimize fatigue. Adverse events caused by
fatigue or unsafe situations are almost entirely ruled out, especially since
the experimenter is continuously in the room to monitor the participant's
safety and comfort. Therefore, the physical and psychological burden is
expected to be low, as is the risk of adverse events.