The Effect of Somatosensory Input on Subjective Visual Vertical in Normal Subjects

ABSTRACT

BACKGROUND AND OBJECTIVES: Aims of the study were to determine if the somatosensory input influences on vertical perception by comparing the results with the head or body tilted (15Degree to the right and to the left, and to examine the influence of tactile sensation in the perception of verticality in head lateral positions. MATERIALS AND METHOD: We tested 34 normal subjects in their ability to set a straight line to the perceived gravitational vertical. Measurements were taken in static conditions, sitting upright, head tilted (15Degree, body tilted (15Degree, and head lateral positions (90Degree on the right/left sides with or without physical support under the head. RESULTS: The normal range of the subjective visual vertical (SVV) was 0.65Degree/-.23Degreein upright position. The normal ranges of SVV in head-tilts 15Degreeto the left/right sides were -0.47Degree/-.76Degreeand 1.88Degree/-.94Degree which were significantly different from those in upright position (E-effect). But the normal ranges of SVV in body-tilts 15Degreeto the left/right were not different from those in upright position. And the normal ranges of SVV in head lateral positions maintained actively and passively were not different each other, but significantly larger than that in upright position (A-effect). CONCLUSION: Our results support that neck somatosensory input plays a part in the perception of verticality. In contrast, tactile sensation of the head had no effect on the settings of a visual line to visual vertical in head lateral positions.