Abstract
The degree to which a person relies on visual stimuli for spatial orientation is termed visual dependency (VD). VD is considered a perceptual trait or cognitive style influenced by psychological factors and mediated by central reweighting of the sensory inputs involved in spatial orientation. VD is often measured with the rod-and-disk test, in which participants align a central rod to the subjective visual vertical (SVV) in the presence of a background that is either stationary or rotating around the line of sight-dynamic SVV. Although this task has been employed to assess VD in health and vestibular disease, what effect torsional nystagmic eye movements may have on individual performance is unknown. Using caloric ear irrigation, 3D video-oculography, and the rod-and-disk test, we show that caloric torsional nystagmus modulates measures of VD and demonstrate that increases in tilt after irrigation are positively correlated with changes in ocular torsional eye movements. When the direction of the slow phase of the torsional eye movement induced by the caloric is congruent with that induced by the rotating visual stimulus, there is a significant increase in tilt. When these two torsional components are in opposition, there is a decrease. These findings show that measures of VD can be influenced by oculomotor responses induced by caloric stimulation. The findings are of significance for clinical studies, as they indicate that VD, which often increases in vestibular disorders, is modulated not only by changes in cognitive style but also by eye movements, in particular nystagmus.
Highlights
Participants made verticality judgments using the rod-anddisk test, a test of visual dependence, and repeated after caloric irrigation
Witkin and Asch first reported that when participants were presented with visual cues to verticality that were tilted with respect to true gravitational vertical, a proportion of the population incorrectly estimated that they themselves were tilted with respect to true vertical in the direction of the visual reference frame tilt (Witkin and Asch 1948)
In experiment 1, the slow phases of the torsional nystagmus from the visual stimulus and caloric stimulus were in the same direction
Summary
Participants made verticality judgments using the rod-anddisk test, a test of visual dependence, and repeated after caloric irrigation. The influence that moving visual stimuli have on the perception of verticality was explored in a seminal paper aptly titled “Moving visual scenes influence the apparent direction of gravity” (Dichgans et al 1972) This established one of the most frequently employed designs used to measure the effect of visual motion on gravitational verticality judgments, an optokinetic disk rotating in the roll (frontal) plane as the visual stimulus—the rod-and-disk test (Bronstein et al 1996; Dichgans et al 1972; Guerraz et al 2001).
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