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Presented at NACOB 98:
North American
Congress
on Biomechanics
Canadian Society for Biomechanics -
American Society of Biomechanics
University of Waterloo
Waterloo, Ontario, Canada
August 14-18, 1998
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POSTURAL SWAY AND ATTENTION
M.S. Redfern 1 and J.R.
Jennings 2
1 Departments of Otolaryngology and
Bioengineering
2 Departments of Psychiatry and
Psychology
University of Pittsburgh, Pittsburgh PA, 15213
INTRODUCTION
This study investigated the relationship
between standing postural control and
cognitive variables (i.e. attention) through a
dual task paradigm. Balance was challenged
with different postural tasks, while secondary
information processing (reaction time) tasks
were required to be performed. The results
showed that the magnitude of postural sway
was not affected by performing the
information processing task; however,
reaction times were increased as the postural
task difficulty was increased.
REVIEW AND THEORY
Standing balance is maintained through the
integration of sensory information provided
by the visual, proprioceptive and vestibular
systems. Until recently, postural control was
thought to be an automatic process, requiring
little or no attention. However, there is some
evidence that this may not be true. Dual task
paradigms have suggested that as standing
posture becomes more difficult, increase
attentional resources are required (Teasdale et
al., 1993; Lajoie, et al., 1993). However, this
relationship is not yet clear. In alert, young
healthy adults, increased use of cognitive
resources is not always found (Schlesinger,
et al., 1997). The purpose of this study was
to investigate the role of attention in standing
postural control through a dual task paradigm
by varying the difficulty of the standing
conditions and the difficulty of the secondary
information processing (reaction time) task.
PROCEDURES
Sixteen young healthy subjects (20 - 25 yrs)
participated in the study. Subjects stood on a
posture platform while performing reaction
time (RT) tasks. The posture platform
provided sway referenced (i.e. subject-fixed)
floor and/or scene movements during
concurrent RT tasks. The postural tasks
were: a) seated, b) standing on a fixed floor,
c) sway referenced floor, d) sway referenced
floor and scene, and e) pseudo-random
antero-posterior translations (translating
floor). The attentional tasks were: 1) No task
(control), 2) Reaction time response to a
visual stimulus, 3) Reaction time response to
an auditory stimulus, and 4) an inhibition
task. For the simple RT task, a light emitting
diode (LED) was placed on the visual
surround in front of the subject at eye level or
a tone through headphones. A button
provided the subject’s response to the LED
stimulus. Simultaneously, foot forces were
recorded throughout the trial. Data were
acquired at 1 kHz. For the inhibition RT
task, subjects were provided a precisely
timed tone and a “Go-No-Go” paradigm was
used. Subjects were instructed to respond as
fast as possible to an LED stimulus by
pressing the button. However, if a tone was
heard concurrently with the LED
presentation, then the subject was told to
inhibit the response and not press the button.
Twenty percent of the stimuli during the
inhibition trials included a tone to require
inhibition. The dependent measures were: a)
reaction time and b) postural sway via center
of pressure (COP) recordings. The
parameters of sway used in the analysis was
the root-mean-square (RMS) of the COP.
RESULTS
Sway During Simple Reaction Time
Tasks: Postural sway while performing a
simple reaction time task did not significantly
differ when comparing the concurrent
performance of an auditory versus a visual
stimulus (p=.75). This was true across all
postural conditions. This result was
hypothesized; however, there was concern
that focussing on a visual target could
interfere with the visual component of
postural control.
Sway During Reaction Time Tasks: An
ANOVA was performed on the RMS of the
postural sway, investigating the effects of the
independent variables RT task (none, simple,
inhibition) and Postural Condition (Fixed,
Sway Referenced, Translations, and Sway
referenced floor and scene). Antero-posterior
RMS sway was significantly affected by
postural condition (p<.001), but not
significantly affected by RT task (p=.43) nor
the interaction (p=.89).
(Figure 1)
Reaction Times During Postural
Conditions: An analysis of the effect of
postural conditions on reaction times
revealed that postural condition had a
significant effect (p<.01) on reaction times
for both the simple reaction time tasks and
the inhibitory reaction time tasks. (Figure 2)
DISCUSSION
The results of this study showed that the
performance of the informational processing
task did not have an effect on postural sway
in young healthy subjects. However, postural
condition did influence the performance on
the informational processing task. As the
difficulty of the postural task was increased,
performance on the reaction time task
worsened. This was true in both simple
reaction time tasks and more difficult
inhibitory reaction time tasks. Thus,
postural control appears to require cognitive
resources (i.e. attention) to maintain balance
in young healthy adults.
Figure 1: Mean RMS sway
(+s.d.) versus
postural condition during simple and
inhibitory RT tasks.
Figure 2: Mean reaction times
(+s.e.) while
standing in different postural conditions.
REFERENCES
Teasdale, et al. Exp. Brain Res., 19, 1-13, 1993.
Lajoie, et al., Exp Brain Res., 97, 139-144, 1993.
Schlessinger, et al., Neuroreport, 9, 49-52, 1998.
ACKNOWLEDGMENTS
This research was supported by NIH grant
AG R01-14116.
