Eye movements during measurements of visual vertical in the post-stroke subacute phase

The subjective visual vertical (VV), the visually estimated direction of gravity, is essential for assessing vestibular function and visuospatial cognition. In this study, we aimed to investigate the mechanisms underlying altered VV perception in stroke participants with unilateral spatial neglect (USN), specifically by examining their eye movement patterns during VV judgment tasks. Participants with USN demonstrated limited eye movement scanning along a rotating bar, often fixating on prominent ends, such as the top or bottom. This suggests a reflexive response to visually salient areas, potentially interfering with accurate VV perception. In contrast, participants without USN showed broader scanning around the center of the bar. Notably, participants with USN without frontal lobe lesions occasionally exhibited extended scanning that included the bar's center, which was associated with accurate VV judgments. These findings suggest that (1) a tendency to fixate on peripheral, prominent areas and (2) frontal lobe involvement in disengaging and redirecting spatial attention may influence VV perception in USN. Based on these results, targeted rehabilitation strategies that encourage individuals with USN to extend their visual scanning beyond prominent endpoints and include central areas could improve VV accuracy. This study highlights the specific eye movement behaviors contributing to VV misperception, emphasizing the importance of training that broadens scanning to improve VV perception effectively.Significance Statement While subjective visual vertical (VV) assessment requires visually judging a rotating bar's verticality, stroke participants with unilateral spatial neglect (USN) exhibit impaired VV perception. However, the underlying mechanisms remain unclear. Through analyses of eye movement patterns, this study demonstrates shorter eye scan lengths along the bar and focused gaze on conspicuous parts of the bar among participants with USN, which disrupts the integration of vestibular and visuospatial processes. Further, USN participants without frontal lobe lesions show occasional improvements in VV perception with broad eye scans around the center of the bar, indicating a frontal lobe's role in visuospatial disengagement and updating the mechanisms in verticality sensation. These findings underscore the significance of understanding visual search patterns for effective USN rehabilitation.