Abstract
Gazing at objects at a near distance (small eye-object distance) can reduce body sway. However, whether body sway is regulated by movement in the mediolateral or anteroposterior direction remains unclear. Galvanic vestibular stimulation (GVS) can induce body tilting in the mediolateral or anteroposterior direction. This study examined the directionality of the eye-object distance effect, using body-tilting GVS manipulations. Ten healthy subjects (aged 21.1 ± 0.3 years) stood on a force plate covered with a piece of foamed rubber and either closed their eyes or gazed at a marker located 0.5 m, 1.0 m, or 1.5 m in front of them. The GVS polarities were set to evoke rightward, forward, and backward body tilts. To compare the effects of eye-object distance in the mediolateral and anteroposterior directions, the root mean square (RMS) of the center of pressure (COP) without GVS was subtracted from the COP RMS during GVS. For swaying in the mediolateral direction, significant visual condition-related differences were found during rightward and forward GVS (p < 0.05). Thus, reductions in mediolateral body sway are more evident for smaller eye-object distances during rightward GVS. It would be appropriate to use body-tilting GVS to detect the directionality of the eye-object distance effect.
Highlights
Information from multiple sensory systems is integrated in the central nervous system to provide appropriate physical responses and achieve postural control during upright standing [1]
In the ML direction of pre-Galvanic vestibular stimulation (GVS) root mean square (RMS) comparison between visual conditions, values in the eyes-closed condition were significantly larger than values in the eye-open conditions (0.5 m, p = 0.002; 1.0 m, p = 0.002; 1.5 m, p = 0.004)
During rightward body-tilting (Figure 2a), the ML center of pressure (COP) RMS value for an eye-object distance of 0.5 m was smaller compared with the eyes-closed and 1.5 m ML COP RMS values (Z = 2.54, p = 0.006, r = 0.80; Z = 2.46, p = 0.01, r = 0.78, respectively)
Summary
Information from multiple sensory systems (visual, vestibular, and proprioceptive) is integrated in the central nervous system to provide appropriate physical responses and achieve postural control during upright standing [1]. Gazing at nearby objects (small eye-object distance) can reduce body sway during upright standing [3,4], this phenomenon may be caused by the ability to detect vision and eye movement information, such as proprioception of oculomotor muscles and motion parallax [5]. Small eye-object distances might facilitate the sensory reweighting of visual information during postural responses. It remains controversial whether this effect is evident as body sway in both mediolateral (ML) and anteroposterior (AP) directions [3,6], or only in the ML direction [7,8]
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