8. Effect of concurrent cognitive tasks on gait features among children post-severe traumatic brain injury and typically-developed controls

post-TBI as compared to
an increase of 0.05� 0.03 seconds among TD
children (p<0.01).
Step length
In addition, step length was significantly different
between trials (F2;50¼ 13.9, p<0.01). Step length
was significantly shorter at the sound assignment. It
was shorter by a mean of 9.48� 2.2 cm as compared
to the baseline value and by 5.9� 1.1 cm as com-
pared to number assignment.
Step length and step time variability
Step length and step time variability were signifi-
cantly higher among children post-TBI across the
assignments, with no significant difference between
the assignments (step length variability, mean
between groups difference 12.2� 2.2, F1;25¼ 8.3,
p< 0.01, step time variability mean between groups
difference 7.9� 2.6, F1;25¼ 9.2, p< 0.01).
Discussion
The present study examined the effects of concur-
rent cognitive tasks on gait performance in children
post-TBI in comparison to TD controls. There was a
negative effect on walking performance when the
children did a concurrent task and this effect was
task-dependant. During the auditory assignment, the
performance error rate was significantly higher as
compared to the memorization assignment and the
effect on walking was more detrimental: walking
speed decreased and step time increased significantly
in the auditory assignment in both groups but with a
Table II. Gait parameters in children post-TBI and TD controls in usual walking and in the two dual task conditions.
Usual walking Dual task- numbers Dual task- sounds
^p-value #p-valueTBI TD *p-value TBI TD TBI TD
Velocity 1.2�0.3 1.3� 0.1 0.15 0.8� 0.2 1.3� 0.2 0.7� 0.1 1.1� 0.2 <0.01 <0.01
Step length 59.1�10.1 66.1� 6.1 0.02 51.2� 11.1 65.4� 5.7 43.9� 11.7 58.7� 8.0 <0.01 0.58
Step length variability 9.3�9.1 8.2� 10.2 0.27 13.4� 14.6 5.4� 3.0 24.0� 17.0 8.4� 5.7 0.12 0.53
Step time 0.45�0.07 0.48� 0.05 0.55 0.60� 0.11 0.51� 0.07 0.61� 0.09 0.53� 0.06 <0.01 <0.01
Step time variability 11.5�15.4 6.8� 7.6 0.23 13.6� 10.1 6.8� 4.8 16.2� 7.8 8.6� 9.2 0.15 0.80
*p-value between groups at usual walking (t-test).
^p-value within subjects (usual walking, numbers, sounds) (Repeated measure ANOVA).
#p-value interaction effect group and manipulation (Repeated measure ANOVA).
584 M. Katz-Leurer et al.
significantly prominent effect among children
post-TBI.
The interference effects of concurrent cognitive
tasks on locomotor performance has been assessed
and described before among children as well as
among adults [12, 17, 18]. It has been suggested that
the outcome of dividing attention between two
concurrent tasks depends on the type and level of
difficulty of the tasks and on the priority given to
each task [3, 4]. Since attention resources are
limited, two tasks will compete for resources if they
are carried out at the same time. They may interfere
with each other when the total amount of resources
demanded exceeds those available.
In the present study, the auditory assignment
caused greater interference than the memorization
assignment. It might be that memorizing a set of
three numbers is a simple memory task which
requires short-term learning and recall as compared
to the sound recognition assignment which involves
identification, recall of existing knowledge and
naming capabilities. The auditory assignment is
clearly more demanding and requires more attention
resources [4, 5, 18]. In previous studies, the negative
effect on locomotor speed while performing second-
ary tasks involving processing of sensory stimuli was
higher than for those involving other types of
cognitive processing. Specifically, it has been noted
that an auditory identification task produced greatest
interference effects on gait than other concurring
tasks [12].
One may claim that the lower effect of the
concurrent cognitive task on gait characteristics in
TD children is due to the fact that the cognitive task
was too simple for them. It has been suggested
before that it is essential to adjust the task difficulties
to the individual’s capacity [19]. However, it has also
been noted that even with a very light overall load on
the cognitive system a difference between patients
with brain damage and healthy controls could be
detected [20]. In this study the memorization and
the auditory assignments were adjusted to the
capabilities of children post-severe TBI. By doing
so one may reduce any significant baseline differ-
ences between groups, but it is argued that any
reduced ability in performance is the result of the
demand to combine performances.
One of the most frequent cognitive limitations
among children post-TBI is an attention distur-
bance. Performing dual tasks demands splitting
attention simultaneously between two tasks and
each assignment might be too difficult to perform
in those whose attention ability is reduced. It has
been well established that when combining cognitive
and walking tasks, the walking requires attention
[21] and dual tasking is sensitive enough to distin-
guish between patients post-concussion from control
subjects [22, 23]. The interactions between concur-
rent tasks cannot be automatically generalized and
should be assessed in different conditions and
modalities. This may imply that the attention
needed for motor and cognitive activities are not
necessarily always competitive and interruptive.
Step variability increases when step velocity
decreases [24]. Therefore, the dual-task related
increase in step length variability shown in this
study could also be explained by the dual-task
related decrease in step velocity. However, the
results of this study show that the decrease in step
velocity while performing the memorization task did
not modify step variability. During the auditory
assignment the mean step time was the same as for
the memorization assignment, but step variability
increased significantly in both groups, more so in the
children post-TBI. This suggests that the increase in
step variability was task-specific, in contrast to
step time.
These findings have clinical implications for the
physiotherapist. Firstly, therapists use a lot of verbal
instructions and feedback during the actual treat-
ment. Therefore, a child post-severe TBI who is
practicing a new and higher level of motor perfor-
mance will benefit more from instructions or feed-
back given before or after performing the task. On
the other hand, if the child needs further refinement
of an achieved motor skill and the therapist indeed
wants to challenge the child, the therapist can
provide concurrent feedback or add a secondary
cognitive task. Another clinical implication is related
to the finding that step variability increases during
dual task performance. It has been noted before that
step variability is associated with balance
performance among children post-TBI [13],
a higher step variability being associated with poor
balance.
Possible, the therapist should work on improving
balance as much as possible before progressing to
higher motor skills. However, Silsupadol et al. [25]
described two adults patients who received balance
training under dual task conditions. Benefits were
maintained over 3 months, whereas they were not
evident in a patient who trained under a single task
balance training programme. The question of
whether training under dual task conditions is
more effective in improving gait after the patient
has progressed in the single task performance needs
further investigation.
The therapist might instruct the family of a child
post-TBI to avoid cognitive tasks in the early stages
of motor training. Dual tasking and adding cognitive
activities while walking should, however, be intro-
duced as an effort to improve the child’s ability to
perform dual tasks in a safe and functional manner.
Effect of concurrent cognitive tasks on gait 585
Declaration of Interest: The authors report
no conflicts of interest.