, Volume 195, Issue 4, pp 621-626
Date: 05 May 2009

Head roll dependent variability of subjective visual vertical and ocular counterroll

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We compared the variability of the subjective visual vertical (SVV) and static ocular counterroll (OCR), and hypothesized a correlation between the measurements because of their shared macular input. SVV and OCR were measured simultaneously in various whole-body roll positions [upright, 45° right-ear down (RED), and 75° RED] in six subjects. Gains of OCR were −0.18 (45° RED) and −0.12 (75° RED), whereas gains of compensation for body roll in the SVV task were −1.11 (45° RED) and −0.96 (75° RED). Normalized SVV and OCR variabilities were not significantly different (P > 0.05), i.e., both increased with increasing roll. Moreover, a significant correlation (R 2 = 0.80, slope = 0.29) between SVV and OCR variabilities was found. Whereas the gain of OCR is different from the gain of SVV, trial-to-trial variability of OCR follows the same roll-dependent modulation observed in SVV variability. We propose that the similarities in variability reflect a common otolith input, which, however, is subject to distinct central processing for determining the gain of SVV and OCR.