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Michiteru Kitazaki, Takuya Kimura; Frequency-phase analysis of postural sway induced by visual motion and galvanic vestibular stimulation. Journal of Vision 2008;8(6):1046. doi: 10.1167/8.6.1046.
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© ARVO (1962-2015); The Authors (2016-present)
Postural control is influenced by vision and vestibular senses. The purpose of this study was to investigate temporal properties of visual, vestibular and cross-modal controls of posture. Visual motion of random-dots (5000dots, lateral cyclic motion, sinusoidal speed modulation, travel distance 11.6deg) was presented on a large-screen (width 2.43 × height 1.82m) by a rear-projector. Galvanic vestibular stimulation (GVS) was applied through left and right mastoid processes (0.1–0.5mA, sinusoidal amplitude modulation). Both visual motion and GVS induced lateral (leftward-rightward) postural sway back and forth. Observers' center of pressure was measure by a force plate at 60Hz.
In Experiment 1, either visual motion or GVS was presented for each trial. We varied the frequency of visual motion and GVS modulation at 0.1, 0.2, and 0.3Hz. Thus, the independent variables were the stimulus modality (Vision or GVS) and the frequency (0.1, 0.2, 0.3Hz). The sway data were analyzed using FFT, and its power and phase at the stimulus frequency were calculated. In results, GVS induced much stronger sway than visual motion. The GVS-induced sway was weaker for 0.3Hz modulation than lower frequencies. Phase (lag) of induced sway increased as stimulus frequency became higher (Vision: 13, 15, 20deg for 0.1, 0.2, 0.3Hz, GVS: 28, 97, 124deg). These results suggest that temporal lag of sway behind sensory stimuli is not accounted by phase constant, but better understood by time constant (250ms for vision, 1100ms for GVS) or their combination.
In Experiment 2 for the cross-modal sway, both visual motion and GVS were presented at the same frequency (0.2Hz) with different phase lags (0–360deg at 45deg step). We found the Visual-and-GVS-induced sway was strongest when vision lagged 90deg behind GVS, and weakest when GVS lagged 90deg behind vision. These results suggest that the vision and GVS are integrated in a weak fusion model to control posture.
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