Affiliations: [a] Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, MD, USA | [b] Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins University School of Medicine, Baltimore, MD, USA | [c] Department of Ophthalmology, National Institute of Neurology and Neurosurgery, National Autonomous University of México, México City, México
Correspondence:
[*]
Corresponding author: Amir Kheradmand, Oculomotor Lab, Department of Neurology, The Johns Hopkins Hospital, Path 2-210, 600 N. Wolfe street, Baltimore, MD 21287, USA. Tel.: +1 410 955 3319; Fax: +1 410 614 1746; E-mail:akherad@jhu.edu
Abstract: BACKGROUND: Perception of upright is often assessed by aligning a
luminous line to the subjective visual vertical (SVV). OBJECTIVE: Here we investigated the effects of visual line rotation
and viewing eye on SVV responses and whether there was any change with head
tilt. METHODS: SVV was measured using a forced-choice paradigm and by
combining the following conditions in 22 healthy subjects: head position
(20° left tilt, upright and 20° right tilt), viewing eye (left
eye, both eyes and right eye) and direction of visual line rotation
(clockwise [CW] and counter clockwise [CCW]). RESULTS: The accuracy and precision of SVV responses were not
different between the viewing eye conditions in all head positions (P> 0.05,
Kruskal-Wallis test). The accuracy of SVV responses was % significantly
different between the CW and CCW line rotations (p ≈ 0.0001;
Kruskal-Wallis test) and SVV was tilted in the same direction as the line
rotation. This effect of line rotation was however not consistent across
head tilts and was only present in the upright and right tilt head
positions. The accuracy of SVV responses showed a higher variability among
subjects in the left head tilt position with no significant difference
between the CW and CCW line rotations (P> 0.05; post-hoc Dunn's test). CONCLUSIONS: In spite of the challenges to the estimate of upright
with head tilt, normal subjects did remarkably well irrespective of the
viewing eye. The physiological significance of the asymmetry in the effect
of line rotation between the head tilt positions is unclear but it
%may suggest
suggests
a lateralizing effect of head tilt on the visual perception of upright.
Keywords: Subjective visual vertical, head tilt, line rotation, monocular, binocular
