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Abstract
The purpose of this study was to determine whether significant attentional resources
are required to accurately monitor changes in bodily orientation, using vestibular
information. This question was addressed firstly using a dual-task paradigm in which
orientation perception tasks and a speeded auditory tone discrimination task were
carried out either singly or in combination. For the active orientation perception
task, subjects were seated in darkness on a motorised chair which could be rotated
about an earth-vertical axis. Following passive angular displacements, subjects were
required to return the chair to their perceived starting position, using a joy-stick
which controlled chair motion. For the speeded auditory task, subjects pushed a hand-held
button as fast as possible when a tone was presented over headphones. When the two
tasks were combined, reaction times on the auditory task increased. Reaction time
also increased when subjects were simply asked to fixate during rotation. A second
experiment demonstrated that if attention was occupied by performance of a demanding
mental arithmetic task during the passive rotation, accuracy of subsequently repositioning
the chair to the origin declined, implying that change in orientation had been less
accurately registered when performing the concurrent mental task. In combination,
these findings indicate that a small but significant degree of attention or cognitive
effort is necessary to monitor accurately the direction and amplitude of a brief angular
rotation, and to suppress vestibulo-ocular reflex eye movement.