A complicated sensory system is important for postural control under natural conditions. The visual, vestibular, and somatosensory systems are major contributors to human postural stability [1][2][3]. A reduction of sensory information from the above systems disturbs the standing balance in humans. There is considerable evidence for vestibularly driven disturbances [4]. With the eyes closed, body sway in the frontal and sagittal directions increases by 54% [3].Afferent information from the above sensory systems is important for human spatial orientation and postural control. A few papers have focused on the effect of the auditory system on postural control. However, this effect is rather ambiguous. Auditory stimulation, especially stationary auditory fields, may at times cause an increase, producing a destabilizing effect [5,6], and at other times a slight decrease in the amplitude of body sway [7].There are only two papers describing the influence of moving auditory fields on postural reactions. An illusion of a moving sound source was created in both of them [8,9]. In one paper [8], an illusion of movement was created by switching the sound between two loudspeakers with a front-back or a right-left arrangement relative to a subject's head. An auditory image moved in either the sagittal (front-back or back-front) or the frontal (left-right or right-left) plane. It was found that, with sound stimuli presented, the amplitude of the body sway was greater than that observed in silence and was direction-dependent, slightly increasing in the direction of the auditory image movement. For example, when an auditory image moved from the front to the back of a subject's head, the amplitude of the body sway increased in the sagittal plane.In the other paper [9], an illusion of movement was created with a special device controlling the binaural sound parameters. When heard through headphones, the auditory image moved clockwise or counterclockwise in a horizontal plane at the subject's head level. It was found that the moving sound signal specifically affected the shift of the general center of gravity (GCOG). Yet, no differences were revealed for the effect of the direction of auditory image movement (clockwise or counterclockwise) on the postural reactions.The objective of this work was to study the human postural reactions to sound source movement in the vertical (sagittal) plane. METHODSThe study involved five subjects (four females and one male) aged 17-40 years without vestibular pathologies and with normal hearing.The subjects were tested in an anechoic room. For auditory stimulation, 53 loudspeakers were equally spaced along an arc with a radius of 1 m and a total angular distance of 180° . The arc was fixed vertically. During the study, a subject stood upright on a platform with his or her hands stretched along the body. The platform was centered relative to the arc so that the sagittal plane of the subject coincided with the plane of the arc. In this position, forward and backward sways of the body (the sagittal pla...

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The effects of moving sound sources on postural responses were studied. Sound source movement was simulated by sequential switching of loudspeakers located along an arch positioned in the sagittal plane relative to the subject. The total durations of the sound stimulus movement were 1.6, 3.2, and 4.8 sec. Signals of 1.6 and 3.2 sec led to decreases in the mean amplitude of oscillogram oscillations in the sagittal and frontal planes. Stabilogram curves averaged for all subjects for the signal of duration 4.8 sec showed that the center of gravity deviated during exposure to the sound stimulus towards the side opposite the direction of movement of the sound source.

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