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 audi tory tone discrimination task were carried out either singly or in combinat ion. For the active orientation perception task, subjects were seated in da rkness on a motorised chair which could be rotated about an earth-vertical axis. Following passive angular displacements, subjects were required to re turn the chair to their perceived starting position, using a joy-stick whic h controlled chair motion. For the speeded auditory task, subjects pushed a hand-held button as fast as possible when a tone was presented over headph ones. 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 t he passive rotation, accuracy of subsequently repositioning the chair to th e origin declined, implying that change in orientation had been less accura tely registered when performing the concurrent mental task. In combination, these findings indicate that a small but significant degree of attention o r cognitive effort is necessary to monitor accurately the direction and amp litude of a brief angular rotation, and to suppress vestibule-ocular reflex eye movement. (C) 1999 Elsevier Science Ltd. All rights reserved.