Attentional demands of perception of passive self-motion in darkness.

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.