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Abstract:
Unilateral transcutaneous mechanical vibration (TMV) of the
posterior neck muscles has been shown to temporarily relieve some
symptoms of hemineglect and to shift normal subjects' perception of
their body midline. This study investigates the mechanisms that
produce these effects. Some researchers attribute them to a change
in the egocentric representation of space brought about by
proprioceptive input from muscle spindle fibers in the neck. In our
study, 24 undergraduate students were asked to adjust a target
until it fell directly in front of their body midline. As with
previous studies, we found that subjects' estimations of their
midline were shifted in the direction of vibration during
unilateral TMV. However, the magnitude of the shift was greater for
subjects who received left unilateral TMV than for those that
received right unilateral TMV. Additionally, the magnitude of shift
was greater when the target was presented at 60 cm than when it was
presented at 40 cm, with no interaction for side of stimulation.
These findings support the idea that there may be different
representations of near and far space and indicate that the effects
of unilateral TMV are not completely attributable to simple
proprioceptive input from the muscle spindle fibers.
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