Visual perception of upright: Head tilt, visual errors and viewing eye

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 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 suggests a lateralizing effect of head tilt on the visual perception of upright.

Perception of Upright: Multisensory Convergence and the Role of Temporo-Parietal Cortex

“…This effect has been attributed to ocular torsion induced by changes in the vergence angle of the eyes (i.e., cycloversion). The viewing eye (i.e., monocular or binocular viewing), on the other hand, does not significantly affect SVV errors, neither in upright position nor during head tilt ( 6 , 18 ).…”

“…For example, the initial orientation of the line stimulus can bias upright perception in the direction of the starting line orientation, and in the opposite direction of the line movement ( 7 – 12 ). This bias, however, may reverse and occur as a “hysteresis” effect in the direction of the line movement when the line is presented in sequential angles in a forced-choice paradigm ( 6 ). Also, with active adjustment of the line, the upright estimate may gradually drift as a result of trial-to-trial dependency of upright adjustments and inter-correlation among consecutive SVV responses ( 13 ).…”

Multisensory contribution in visuospatial orientation: an interaction between neck and trunk proprioception

“…When the whole-body is tilted in the roll plane, SVV normally becomes less accurate such that at small tilt angles (< 60°) the error is often in the opposite direction of the whole-body tilt; a phenomenon known as the Müller or E-effect (Aubert 1861 ; Müller 1916 ; Witkin and Asch 1948 ; Kheradmand et al 2016 ). Our results, however, show that the trunk tilt alone led to SVV errors in the same direction of the tilt.…”

“…The head tilt condition alone was not included in the current design as this effect has been widely investigated previously (Wade 1968;Dichgans et al 1974;Young et al 1975;Tarnutzer et al 2010;Kheradmand et al 2016;Otero-Millan and Kheradmand 2016), and reference to head tilts with upright body in the discussion is thus inferred from previous published data rather than a direct observation in our study.…”