Abstract
This study assessed the pupil responses in the sensory integration of various directional optic flows during the perception of gravitational vertical. A total of 30 healthy participants were enrolled with normal responses to conventional subjective visual vertical (SVV) which was determined by measuring the difference (error angles) between the luminous line adjusted by the participants and the true vertical. SVV was performed under various types of rotational (5°/s, 10°/s, and 50°/s) and straight (5°/s and 10°/s) optic flows presented via a head-mounted display. Error angles (°) of the SVV and changes in pupil diameters (mm) were measured to evaluate the changes in the visually assessed subjective verticality and related cognitive demands. Significantly larger error angles were measured under rotational optic flows than under straight flows (p < 0.001). The error angles also significantly increased as the velocity of the rotational optic flow increased. The pupil diameter increased after starting the test, demonstrating the largest diameter during the final fine-tuning around the vertical. Significantly larger pupil changes were identified under rotational flows than in straight flows. Pupil changes were significantly correlated with error angles and the visual analog scale representing subjective difficulties during each test. These results suggest increased pupil changes for integrating more challenging visual sensory inputs in the process of gravity perception.
Highlights
This study assessed the pupil responses in the sensory integration of various directional optic flows during the perception of gravitational vertical
Ocular torsion induced by the rotating optokinetic flow has been suggested as an underlying physiologic mechanism that biases the perception of verticality, especially when the subjective verticality was assessed in a visually controlled way, such as the subjective visual vertical (SVV)[12,13,14,15]
We aimed to evaluate the cognitive demands required to integrate confusing optokinetic stimuli during the subjective perception of verticality by assessing pupil changes
Summary
This study assessed the pupil responses in the sensory integration of various directional optic flows during the perception of gravitational vertical. Error angles (°) of the SVV and changes in pupil diameters (mm) were measured to evaluate the changes in the visually assessed subjective verticality and related cognitive demands. Pupil changes were significantly correlated with error angles and the visual analog scale representing subjective difficulties during each test. These results suggest increased pupil changes for integrating more challenging visual sensory inputs in the process of gravity perception. The determination of subjective verticality could require a considerable amount of cognitive resources as the process has to evaluate and integrate multiple sensory information. Among the clinical tests for vestibular functions, pupil response can be preferentially applied to the SVV because it is performed in a dark visual field with minimal eye movement, making it easy to reliably measure the pupil size
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